bluuebunny/crossref_metadata_2025 huggingface dataset:
Implementation of an efficient scheme for calculating nonlinear transfer from wave‐wave interactions
Authors: Snyder R. L. , Thacker W. C. , Hasselmann K. , Hasselmann S. , Barzel G.
Published: February 2008

Nonlinear transfer from wave‐wave interactions is an important term in the action‐balance equation governing the evolution of the surface‐gravity‐wave field. Computation of this term, however, has hitherto been so consuming of computer resources that its full representation has not been feasible in nonparametric two‐dimensional computer models of this equation. This paper describes the implementation of a hybrid computational scheme, incorporating a simplification first proposed by Thacker into the EXACT‐NL Boltzmann integration scheme of Hasselmann and Hasselmann. This hybrid scheme retains EXACT‐NL's symmetry, precision, and two‐stage structure, but, by transferring a spectrum‐independent preintegration from the second stage to the first, dramatically accelerates the resulting second‐stage computation, enabling a relatively efficient and precise determination of nonlinear transfer in two‐dimensional wave models. Physically, this preintegration collects together in single hybrid interactions multiple interactions belonging to identical spectral‐band quadruplets. Thus all possible interactions are represented, and these interactions are represented in a uniquely efficient manner consistent with the spectral representation. We compute the coefficients in the resulting second‐stage hybrid sum by essentially sorting and pre‐summing the coefficients generated by a piecewise‐constant first‐stage EXACT‐NL computation, using a variant of EXACT‐NL that replaces the gather‐scatter operations with a simpler bin‐assignment procedure and employs a somewhat simpler set of integration variables. By exploiting the natural scaling of the integrand and partially pre‐summing prior to sorting, we are able to further improve the efficiency of this computation for the deep‐water case and to refine its integration‐grid resolution almost to convergence. In wave‐model computations of nonlinear transfer, vectorization on the spatial grid points of the model and selective truncation of the hybrid sum potentially reduce the working computation time for a single model time step to well under one Cray Y‐MP single‐processor CPU second per hundred grid points, while preserving a remarkably faithful representation of the full transfer.
A chlorofluoromethane and hydrographic section across Drake Passage: Deep water ventilation and meridional property transport
Authors: Roether Wolfgang , Schlitzer Reiner , Putzka Alfred , Beining Peter , Bulsiewicz Klaus , Rohardt Gerd , Delahoyde Frank
Published: February 2008

New hydrographic and nutrient data obtained on a section across Drake Passage (F/S Meteor January 1990, World Ocean Circulation Experiment Hydrographic Program section S1) are in close agreement with property sections reported previously. The chlorofluoromethanes CFM 11 and CFM 12 were measured in Drake Passage for the first time. CFM concentrations are found to decrease from the surface down into the Upper Circumpolar Deep Water, for which they confirm water renewal from the south. For the Lower Circumpolar Deep Water, in which CFM concentrations were above detection limit only south of the Polar Front, very little water renewal on the CFM time scale is implied. Nonvanishing CFM is again found in the Weddell Sea Deep Water and the Southeast Pacific Deep Water toward the bottom in the south, but recent ventilation for the latter water mass is rejected. CFM 11 and CFM 12 concentrations vary essentially in constant proportion down to very low concentrations, questioning the possibility of using CFM ratios as “age” markers. The observed ratios are shown to be a natural feature of the upwelling regime of the southern ocean. Property concentrations on isopycnal surfaces display large undulations, reaching down into the Upper Circumpolar Deep Water. Their extrema, due to varying contribution of young water of southern origin, are situated at the boundaries of the current bands of the Antarctic Circumpolar Current The feature is ascribed to property advection by rings and is taken to support previous claims that rings are an important transport mechanism across the Antarctic Circumpolar Current and that they might assist in maintaining its fronts.
Geosat and advanced very high resolution radiometer observations of oceanic planetary waves adjacent to the Hawaiian Islands
Authors: Van Woert Michael L. , Price James M.
Published: February 2008

Geosat observations of the central North Pacific Ocean show westward propagating mesoscale features with length scales (>500 km), time scales (105–155 days), and observed zonal phase speeds commensurate with those of nearly nondispersive baroclinic Rossby waves. Advanced very high resolution radiometer‐derived sea surface temperatures observed during April 1988 showed a cusp‐shaped pattern north of the Hawaiian Islands congruent with concurrent Geosat‐derived sea level height anomalies. It is believed that the cusp‐shaped pattern is the surface manifestation of a baroclinic Rossby wave. The observed wavelength of the cusp‐shaped pattern was 560 km. It had an observed meridional extent (horizontal amplitude) of 200–300 km and an inferred zonal propagation speed of 0.052 m s−1. The westward propagating sea level height structure was observed to amplify as it approached 150°W reaching amplitudes of 0.06–0.08 m in the vicinity of the cusp‐shaped feature. These waves are believed to be locally forced by the topography, either as the result of eastward flow over the submerged island ridge or as a result of baroclinic instability during periods of westward flow.
Estimating global air‐sea fluxes from surface properties and from climatological flux data using an oceanic general circulation model
Authors: Tziperman Eli , Bryan Kirk
Published: February 2008

A simple method is presented and demonstrated for estimating air‐sea fluxes of heat and fresh water with the aid of a general circulation model (GCM), using both sea surface temperature and salinity data and climatological air‐sea flux data. The approach is motivated by a least squares optimization problem in which the various data sets are combined to form an optimal solution for the air‐sea fluxes. The method provides estimates of the surface properties and air‐sea flux data that are as consistent as possible with the original data sets and with the model physics. The calculation of these estimates involves adding a simple equation for calculating the air‐sea fluxes during the model run and then running the model to a steady state. The proposed method was applied to a coarse resolution global primitive equation model and annually averaged data sets. Both the spatial distribution of the global air‐sea fluxes and the meridional fluxes carried by the ocean were estimated. The resulting air‐sea fluxes seem smoother and significantly closer to the climatological flux estimates than do the air‐sea fluxes obtained from the GCM by simply specifying the surface temperature and salinity. The better fit to the climatological fluxes was balanced by a larger deviation from the surface temperature and salinity. These surface fields were still close to the observations within the measurement error in most regions, except western boundary areas. The inconsistency of the model and data in western boundary areas is probably related to the inability of the coarse resolution GCM to appropriately simulate the large transports there. The meridional fluxes calculated by the proposed method differ very little from those obtained by simply specifying the surface temperature and salinity. We suggest therefore that these meridional fluxes are strongly influenced by the interior model dynamics; in particular, the too‐weak model meridional circulation cell seems to be the reason for differences between the meridional transports in the model and those estimated from other sources. We discuss the implications for the calculation of air‐sea fluxes by inverse models.
Three‐dimensional Langmuir circulation instability in a stratified layer
Authors: Leibovich Sidney , Tandon Amit
Published: February 2008

Some reports of Langmuir circulations describe windrows at systematic angles to the local wind direction. Other observers find windrows in close alignment to the wind direction, but with a systematic drift sideways to the wind. These effects probably result from more than one physical cause. Here it is shown, by an analysis of the linear stability of the surface layer, averaged to remove surface wave fluctuations, that persistent small windrow angles can result from weak stable density stratification. In these cases, the linearly most unstable modes are found to be weakly three dimensional for the range of parameters considered. Possible surface windrow patterns include rolls mostly parallel to the wind but of finite length, with branching and merging, as well as parallel rolls inclined to the wind and drifting laterally with respect to the wind direction. For unstratified flow, steady two‐dimensional rolls are preferred.
Measurements of absolute absorption cross sections of ozone in the 185‐to 254‐nm wavelength region and the temperature dependence
Authors: Yoshino K. , Esmond J. R. , Freeman D. E. , Parkinson W. H.
Published: February 2008

Laboratory measurements of the relative absorption cross sections of ozone at temperatures 195, 228 and 295 K have been made throughout the 185 to 254 nm wavelength region. The absolute absorption cross sections at the same temperatures have been measured at several discrete wavelengths in the 185 to 250 nm region. The absolute cross sections of ozone have been used to put the relative cross sections on a firm absolute basis throughout the 185 to 255 nm region. These recalibrated cross sections are slightly lower than those of L. T. Molina and M.J. Molina (Journal of Geophysical Research 91, 1450, 1986), but the differences are within a few percent and would not be significant in atmospheric applications.
Non‐local‐thermodynamic‐equilibrium populations of the first vibrational excited state of CO in the middle atmosphere
Authors: López‐Puertas M. , López‐Valverde M. A. , Edwards D. P. , Taylor F. W.
Published: February 2008

A non‐LTE radiative transfer model for the population of the CO(1) vibrational state in the middle atmosphere is presented. Radiative transfer is treated by using the Curtis matrix method. The transmittances needed for the Curtis matrix have been computed by using the GENLN2 line‐by‐line radiance/transmittance code. A study of the radiative and collisional processes and atmospheric parameters that affect the population of CO(1) populations has been performed. We find that the tropospheric kinetic temperature and CO abundance profiles play an important role through radiative coupling in the population of mesospheric CO(1) at night‐time. During the day, the solar flux and the mesospheric CO abundance are the main factors determining the CO vibrational temperature in the mesosphere. Non‐thermal collisions with the atmospheric N2(1) are also shown to be important for the daytime population of CO(1) in that region. The consequences of these results for the retrieval of CO abundances from the remote sensing of radiance at 4.7 μm are discussed.
A 4‐year climatology of stratospheric ozone from lidar measurements at Table Mountain, 34.4°N
Authors: McDermid I. Stuart
Published: February 2008

Regular measurements of stratospheric ozone concentration profiles have been made at Table Mountain, California, since February 1988. During the period up to the end of December 1991, 435 independent profiles were measured by the differential absorption lidar technique. These long‐term results and an evaluation of their quality are presented in this paper. The large number of measurements made has allowed the development of a short‐term, 4‐year, climatology of the ozone concentration profile at this specific location (34.4°N, −117.7°W). The effects of the eruption of Mount Pinatubo were not observed in the lidar measurements until August 1991 and the results presented here can essentially be considered as the pre‐Pinatubo climatology.
Measurement of the abundance of 14CO in the atmosphere and the 13C/12C and 18O/16O ratio of atmospheric CO with applications in New Zealand and Antarctica
Authors: Brenninkmeijer Carl A. M.
Published: February 2008

Equipment and method for accurate and precise concentration, 14C, 13C, and 18O isotope analysis for CO in background air is presented along with new results for Antarctica and New Zealand. High flow rate cryogenic extraction systems which separate CO after its oxidation to CO2 are used, incorporating a novel ultraefficient cryogenic trap. Air in quantities from a few hundred liters to 2 m3 with CO concentrations from 20 part per billion by volume (ppbv) to 1000 ppbv can be analyzed. The absolute CO concentration is determined volumetrically. The 13C/12C and 18O/16O ratios are determined by mass spectrometry. For 18O a correction is applied for the oxygen in the CO2 derived from the oxidant. Carbon 14 is determined by accelerator mass spectrometry. Prior to this the very small CO‐derived samples with their high specific activity are diluted accurately. For polluted air the proportional decrease in specific activity with increasing CO levels is confirmed. The 14CO abundance and CO concentration in background air in New Zealand and Antarctica are not much different, and both follow a distinct seasonal pattern, in particular 14CO which is mainly forced by OH seasonality. The 14CO abundance swings between its February minimum of about 6 and its August maximum of about 13 molecules per cm3 air (STP). CO has a smaller seasonality and shows a larger scatter due to local CO sources. The impact of changes in solar activity on 14CO for the period considered has been small. Most of the short‐term variability in 14CO is due to the sampling of different air masses. It appears that interannual OH variations may be reflected in 14CO variations. Both 13C/12C and 18O/16O at Scott Base show large seasonal variation, and the impact of biomass burning and isotopic fractionation in CO destruction are used to try to explain the respective isotopic compositions.
A comparison of surface stress and precipitation fields in short‐range forecasts over the Antarctic region
Authors: Arpe K. , Cattle H.
Published: February 2008

A comparison is made of wind stresses derived from the European Centre for Medium‐Range Weather Forecasts (ECMWF) and United Kingdom Meteorological Office (UKMO) operational numerical weather prediction models over the Antarctic region for the periods June 1 to July 27,1988, and through July 1990. Comparison of model precipitation fields over the region is also made for the July 1990 period. Mean fields are found to be qualitatively similar over much of the Antarctic sea ice zone, with the largest discrepancy arising through the acceptance of an individual observation by one scheme in this data sparse region and rejection by the other. A particular feature of the comparisons is a large discrepancy in the values of the wind stress shown by the models around the Antarctic coastal zone. These are investigated in detail for the July 1990 period by reference to contemporaneous observations. Both precipitation and surface stress fields reveal a generally high similarity in their variability in space and time overall, illustrating the influence of the observational data on the model fields.
Relationship between radon 222 daughter and ThB concentrations in surface air with atmospheric stability
Authors: Dueñas C. , Fernandez M. C. , Carretero J. , Perez M.
Published: February 2008

The relationship between the decay products of Rn(DRn) and ThB concentrations in the atmospheric air and the stability of the atmosphere has been established. Daily measurements were taken over nearly a 2‐year period (1989–1991). The method used to determine concentrations of DRn and ThB is based on the total alpha activity amount of radioactive aerosols deposited on a filter. The vertical stability of the atmosphere was studied by three methods: Pasquill's stability categories, vertical temperature gradients, and a method based on Montgomery's potential. In the last two cases the relationship between the concentrations in DRn and ThB with stability was higher and more concordant with experimental results than with Pasquill's method.
Effects of soil moisture, temperature, and inorganic nitrogen on nitric oxide emissions from acidic tropical savannah soils
Authors: Cárdenas Laura , Rondón Alberto , Johansson Christer , Sanhueza Eugenio
Published: February 2008

NO fluxes from soils with a wide range of soil moistures, soil inorganic‐N concentrations, and soil temperatures were measured during the wet and the dry season at a Venezuelan savannah site. Maximum NO emissions (∼12 ngN m−2 s−1) were observed at soil gravimetric moistures between 10% and 18%. Deviation from this optimum range results in decreased NO fluxes; very low emissions ( < 2 ngN m−2 s−1 ) were recorded at low ( < 2% ) and high ( > 25% ) soil moistures. Both NO production in soil and its transport within the soil play important roles in the emission of NO to the atmosphere. Under most conditions no temperature effect was observed. NO emission was strongly stimulated by the addition of NO3− and only very weakly by the addition of NH4+; at low and moderate soil moistures, soil nitrate and the NO flux were positively correlated. At low (natural) soil nitrate content and comparable soil moisture and temperature, NO emissions were greater during the dry season than during the rainy season, suggesting that other factors (i.e., soil physical structure) may also govern NO flux from savannah soil.
An intercomparison of aircraft instrumentation for tropospheric measurements of sulfur dioxide
Authors: Gregory Gerald L. , Davis Douglas D. , Beltz Nobert , Bandy Alan R. , Ferek Ronald J. , Thornton Donald C.
Published: February 2008

As part of the NASA Tropospheric Chemistry Program, a series of field intercomparisons have been conducted to evaluate the state‐of‐the art for measuring key tropospheric species. One of the objectives of the third intercomparison campaign in this series, Chemical Instrumentation Test and Evaluation 3 (CITE 3), was to evaluate instrumentation for making reliable tropospheric aircraft measurements of sulfur dioxide, dimethyl sulfide, hydrogen sulfide, carbon disulfide, and carbonyl sulfide. This paper reports the results of the intercomparisons of five sulfur dioxide measurement methods ranging from filter techniques, in which samples collected in flight are returned to the laboratory for analyses (chemiluminescent or ion chromatographic), to near real‐time, in‐flight measurements via gas chromatographic, mass spectrometric, and chemiluminescent techniques. All techniques showed some tendency to track sizeable changes in ambient SO2 such as those associated with altitude changes. For SO2 mixing ratios in the range of 200 pptv to a few ppbv, agreement among the techniques varies from about 30% to several orders of magnitude, depending upon the pair of measurements intercompared. For SO2 mixing ratios <200 pptv, measurements from the techniques are uncorrelated. In general, observed differences in the measurement of standards do not account for the flight results. The CITE 3 results do not unambiguously identify one or more of the measurement techniques as providing valid or invalid SO2 measurements, but identify the range of “potential” uncertainly in SO2 measurements reported by currently available instrumentation and as measured under realistic aircraft environments.
Atmosphere‐snow transfer function for H2O2: Microphysical considerations
Authors: Conklin Martha H. , Sigg Andreas , Neftel Albrecht , Bales Roger C.
Published: February 2008

H2O2 analyses of polar ice cores show an increase in concentration from 200 years to the present. In order to quantitatively relate the observed trend in the ice to atmospheric levels, the atmosphere‐snow transfer behavior and postdepositional changes must be known. Atmosphere‐snow transfer was studied by investigating uptake and release of H2O2 in a series of laboratory column experiments in the temperature range −3°C to −45°C. Experiments consisted of passing H2O2‐containing air through a column packed with 200‐μm diameter ice spheres and measuring the change in gas phase H2O2 concentration with time. The uptake of H2O2 was a slow process requiring several hours to reach equilibrium. Uptake involved incorporation of H2O2 into the bulk ice as well as surface accumulation. The amount of H2O2 taken up by the ice was greater at the lower temperatures. The sticking coefficient for H2O2 on ice in the same experiments was estimated to be of the order of 0.02 to 0.5. Release of H2O2 from the ice occurred upon passing H2O2‐free air through the packed columns, with the time scale for degassing similar to that for uptake. These results suggest that systematic losses of H2O2 from polar snow could occur under similar conditions, when atmospheric concentrations of H2O2 are low, that is, in the winter.
Atmospheric methane at Cape Meares: Analysis of a high‐resolution data base and its environmental implications
Authors: Khalil M. A. K. , Rasmussen R. A. , Moraes F.
Published: February 2008

Between 1979 and 1992 we took some 120,000 measurements of atmospheric methane at Cape Meares on the Oregon coast. The site is representative of methane concentrations in the northern latitudes (from 30°N to 90°N). The average concentration during the experiment was 1698 parts per billion by volume (ppbv). Methane concentration increased by 190 ppbv (or 11.9%) during the 13‐year span of the experiment. The rate of increase was about 20 ± 4 ppbv/yr in the first 2 years and 10 ± 2 ppbv/yr in the last 2 years of the experiment suggesting a substantial decline in the trend at northern middle and high latitudes (−1 ppbv/yr2). Prominent seasonal cycles were observed. During the year, the concentration stays more or less constant until May and then starts falling, reaching lowest levels in July and August, then rises rapidly to nearly maximum concentrations in October. The average amplitude of this cycle is about 30 ± 7 ppbv and has increased during the course of the experiment. Interannual variations with small amplitudes of 2–3 ppbv occur with periods of 1.4 and 6.5 years. The residual concentrations, after accounting for the trends and cycles, have a standard deviation of 6 ppbv for monthly averaged data and 12 ppbv for the daily data. Mass balance calculations show that to explain the observed seasonality of concentrations, the emissions must peak in late summer and early fall (August‐September). No increases in regional annual emissions are required over the last decade to explain the data. For further research, readers may obtain the complete and averaged data from the archives.
SO2 uptake on ice spheres: Liquid nature of the ice‐air interface
Authors: Conklin Martha H. , Bales Roger C.
Published: February 2008

The amount of SO2 gas absorbed by ice of known surface area at equilibrium was used to estimate the volume of liquid water present at the ice‐air interface at temperatures from −1 to −60°C. Calculations were based on Henry's law and acid dissociation equilibrium. The liquid volume is lowest at lower temperatures and ionic strength and under most conditions was greater than the volumes calculated based on freezing‐point depression. The equivalent liquid layer thickness, assuming that liquid water is uniformly distributed around the grains, ranged from 3–30 nm at −60°C to 500–3000 nm at −1°C. Corresponding ionic strengths for the two temperatures were 1.7–0.0012 M and 0.005–0.00009 M. Lower values were for ice made from distilled water, and higher values were for ice made from 10−3 M NaCl. Estimated pH values were from 2.9 at −60°C to 4.1 at −1°C. Results demonstrate that gas absorption can be used to estimate an equivalent liquid volume and thickness for the ice‐air interfacial region. While not directly comparable to physical measurements, the estimated values should be directly applicable to modeling uptake of SO2 and other trace gases by ice. Lack of good thermodynamic data for temperatures below 0°C is the main limitation to applying this method.
Nitric oxide emissions from the high‐temperature viscous boundary layers of hypersonic aircraft within the stratosphere
Authors: Brooks S. B. , Lewis M. J. , Dickerson R. R.
Published: February 2008

Nitrogen oxides have been shown to catalyze the destruction of stratospheric ozone. Previous estimates of nitric oxide emissions from high‐altitude aircraft have taken into account engine emissions only. This study was undertaken to determine whether nitric oxide production in the hot viscous boundary layer surrounding the skin of a hypersonic aircraft can significantly increase estimates of total NO emissions. The described model approximates the viscous boundary layer as a series of finite stream tubes with time‐dependent and temperature‐dependent chemical kinetics and mass flow rates. Nitric oxide equilibrium mole fraction for air peaks at ≅ 3700 K. At hypersonic speeds the viscous effects near the aircraft skin will induce these very high temperatures. Along the skin surface of a 60 m craft, the NO mole fraction can be locally as high as 0.044. Nitric oxide output from this thin boundary layer becomes significant when integrated over the entire trailing edge of the aircraft. This model predicts that nitric oxide production in the boundary layer should be taken into account at speeds above Mach 8. Above Mach 8, boundary layer volume and temperature increase rapidly. At stratospheric speeds approaching Mach 16, the nitric oxide production in the boundary layer increases to the point where it roughly equals the nitric oxide output from the engines. Above Mach 16, the boundary layer produces the majority of the NO emissions. This additional source of nitric oxide will play an ever‐increasing role as aircraft fly at higher speeds and altitudes. Significant errors in total NO emission estimates will result if the viscous boundary layer is not taken into account at speeds above Mach 8.
Application of the Rayleigh lidar to observations of noctilucent clouds
Authors: Meriwether J. W. , Farley R. , McNutt R. , Dao P. D. , Moskowitz W. , Davidson G. , Burka M.
Published: February 2008

The feasibility of lidar detection of noctilucent cloud (NLC) returns with the Rayleigh lidar technique was determined by calculations of lidar photocount profiles for the Nd:YAG lidar wavelength of 532 nm (Rayleigh temperature lidar). These results affirm the feasibility of the application of this instrument to study the high‐latitude summer phenomenon of NLCs. Rayleigh 532‐nm lidar observations were carried out in Greenland for late July and August, 1990. Extended cloudiness hampered these measurements, and a display of NLCs was seen only on August 14–15, 1990, out of a total of 11 nights. Examination of photographs of the NLCs for this night indicates that the spatial distribution of the clouds was patchy and fragmentary. No visual detection of NLCs in the region of the zenith when the solar depression angle was 8.6° was noted. At this time the sky was sufficiently dark, and if there had been any NLCs overhead, visual NLC sightings should have been possible. The lidar observations provided measurements of the middle atmosphere temperature from 25 km to about 70 km for times near local midnight. The shapes of these profiles agreed with that of the U.S. 76 standard model profile but with an increase of about 5% at the stratopause. Examination of the results for an indication of lidar Mie returns from NLCs was negative, which was consistent with the lack of visual detection.
Non‐local thermodynamic equilibrium studies of the 15‐μm bands of CO2 for atmospheric remote sensing
Authors: Edwards David P. , López‐Puertas Manuel , López‐Valverde Miguel A.
Published: February 2008

A new line‐by‐line non‐local thermodynamic equilibrium (non‐LTE) radiance model based on the GENLN2 radiative transfer code is presented. This is capable of high resolution spectral radiance calculations for the upper atmosphere. We describe the non‐LTE model implementation and discuss the molecular state vibrational temperature input requirements for studies of the 15‐μm ν2 bands of CO2. Monochromatic and band‐integrated radiance calculations have been performed for atmospheric limb view tangent heights between 50 and 120 km for non‐LTE nighttime and daytime conditions. Two model atmospheres are considered, the U.S. 1976 Standard and a subarctic summer, which show, respectively, mean and large radiance differences from a reference LTE radiance calculation. Non‐LTE radiance considerations are shown to be important for the 15‐μm CO2 bands for tangent heights greater than 70 km, the magnitude of the divergence from LTE values and diurnal variation being dependent on the band and kinetic temperature profile. We show that the use of the Voigt line shape, rather than the Doppler, is important for tangent heights below 85 km, and that the inclusion of the effect of overlapping lines is a consideration for tangent heights below 75 km. We present calculations of synthetic radiance spectra showing the non‐LTE effect for two CO2 temperature sounding channels of instruments aboard the Upper Atmosphere Research Satellite as a demonstration of the model capability.
Characteristics of wintertime and autumn nitric acid chemistry as defined by Limb Infrared Monitor of the Stratosphere (LIMS) data
Authors: Rood Richard B. , Douglass Anne R. , Kaye Jack A. , Considine David B.
Published: February 2008

Earlier two‐dimensional (2‐D) and three‐dimensional (3‐D) model experiments have shown that the Limb Infrared Monitor of the Stratosphere (LIMS) nitric acid data do not behave as expected from conventional gas phase chemical reactions. As contrasted to two‐dimensional (2‐D) model results, the 3‐D model suggests that the discrepancies are at middle latitudes outside of the polar vortex, rather than at polar latitudes. Using only the data record, the characteristics of the nitric acid behavior arc further examined. The data inside the Aleutian anticyclone are examined during the January wave 1 warming. The anticyclone provides a large isolated region of air that moves from about 40°N to 60°N during the warming. Ozone remains approximately constant during this transit, while nitric acid increases more than 1 parts per billion by volume (ppbv). Both ozone and water vapor fields develop a wave 1 structure during the warming, as expected. Nitric acid, which is also expected to develop a wave 1 signal, develops a prominent wave 2 structure. This structure is observed between 50 and 5 mbar. A prominent feature of the nitric acid field is the persistent “bending” of contours due to strong meridional flow. Since these contours persist, instead of aligning with the flow, there must be chemical processes maintaining the nitric acid with timescales shorter than the advective timescale. The time constant for this chemical process ranges from approximately 1 day at 70°N to about 4 days at 30°N. When the time constant is used in the 3‐D model, all of the basic characteristics of the observations are simulated. It is not clear what chemical mechanisms are responsible for this behavior. There is a strong relationship between the insolation and the shortcomings of the nitric acid simulations. Heterogeneous reactions on background aerosols are considered, but their spatial, temporal, and chemical characteristics are not clearly consistent with the needed changes in the chemistry. If heterogeneous processes are the mechanism, then they are much more complex than currently included in stratospheric models.
Modeling trace gas budgets in the troposphere: 2. CH4 and CO
Authors: Law K. S. , Pyle J. A.
Published: February 2008

A two‐dimensional photochemical model of the atmosphere has been used to calculate regional and global budgets for CH4 and CO in the troposphere. The modeled distributions of these trace gases are compared to relevant observations and show good agreement when the zonal average nature of the model results is taken into account. The chemical and dynamical components of the budgets are investigated and used to explain the seasonal distribution of CH4 and CO in the model. The seasonal variation is governed mainly by the seasonal variation in emissions and transport between the hemispheres. Destruction by OH is also important at certain times of the year.
Cross‐tropopause transport of excess 14C in a two‐dimensional model
Authors: Shia Run‐Lie , Ko Malcolm K. W. , Zou Min , Kotamarthi V. Rao
Published: February 2008

The processed excess 14C data are used to calibrate the cross‐tropopause transport in a two‐dimensional model. The model results are used to diagnose the mechanisms responsible for cross‐tropopause transport in the model and the sensitivity of the transport rate to the changes in the transport parameter. Although the total flux across the tropopause is dominated by the eddy diffusion flux along the isentropic surface due to the large values assigned to the diffusion coefficient Kyy at the boundary, the cross‐tropopause transport is more sensitive to changes in the circulation. Nitrogen oxides emitted by engines of high‐speed civil transport could cause ozone depletion in the lower stratosphere. The expected depletion is proportional to the amount of oxides of nitrogen retained in the stratosphere. For a typical fleet, lowering the tropopause height by 1.2 km can cause a 14–22% increase in the amount of reactive nitrogen retained in the stratosphere. Thus it is necessary to have a fine enough vertical resolution near the tropopause in the two‐dimensional model for determining the stratospheric residence time of the engine emissions deposited near the tropopause.
Mean winds and tides in the upper middle atmosphere at Urbana (40°N, 88°W) during 1991–1992
Authors: Franke Steven J. , Thorsen Denise
Published: February 2008

A summary of the first 18 months of continuous wind observations using the Urbana medium frequency (MF) radar is presented. Emphasis is placed on height‐time contours of monthly mean winds and on amplitudes and phases of 24 hour and 12 hour tides. Results are compared with data from other midlatitude stations and models. Below 85 km, monthly mean winds are shown to agree closely with the zonal mean, geostrophic wind model CIRA86. Significant discrepancies above 85 km have been noted in comparisons between CIRA86 and the other mesosphere‐lower‐thermosphere (MLT) radar stations (including MF, meteor, and low‐frequency (LF) radars) and are also sustained in the observations reported here. Tidal characteristics are generally consistent with other midlatitude observations, although significant differences are noted between Urbana and its closest MLT network neighbor station (Durham, 43°N, 71°W). The mean wind observations provide a context for the gravity wave climatology derived from Na lidar observations at Urbana and promise to contribute toward improvements of middle atmosphere wind and tidal models.
Distribution of methylchloride, dichloromethane, trichloroethene and tetrachloroethene over the north and south Atlantic
Authors: Koppmann R. , Johnen F. J. , Plass‐Dülmer C. , Rudolph J.
Published: February 2008

During the cruise ANT VIII/1 of the German R/VPolarsternin August/September 1989 the latitudinal distributions of the atmospheric concentrations of methylchloride, dichloromethane, trichloroethene, and tetrachloroethene were measured over the Atlantic between 45°N and 30°S by in situ gas chromatography. With the exception of trichloroethene they showed mixing ratios well above the lower limit of detection. The methylchloride distribution was uniform with average mixing ratios of 532 ± 8 and 550 ± 12 ppt in the northern and southern Hemispheres, respectively. Dichloromethane increased linearly between the Intertropical Convergence Zone and 45°N with average mixing ratios of 36 ± 6 ppt and was almost constant in the southern hemisphere with an average of 18 ± 1 ppt. Tetrachloroethene mixing ratios were between less than 1 and 10 ppt in the northern hemisphere and always below 3 ppt in the southern hemisphere. Similar to dichloromethane, tetrachloroethene was nearly constant in the southern hemisphere and increased linearly toward northern latitudes. This is compatible with the predominantly industrial origin of these compounds. Trichloroethene varied between 0.3 ppt and about 15 ppt in the northern hemisphere with an average of 3 ± 1 ppt and was generally lower than 1 ppt in the southern hemisphere with mixing ratios often near or below the detection limit of 0.1 ppt. For CH3Cl we estimate a global turnover of 3.5 × 1012g/yr which is compatible with previous results. Using a simple model calculation our measurements imply a global turnover for CH2Cl2and C2Cl4of 0.9 × 1012g/yr and 0.6 × 1012g/yr, respectively.
Nitric oxide and ozone in the free troposphere over the western Pacific Ocean
Authors: Kondo Y. , Kitada T. , Koike M. , Kawakami S. , Makino Y.
Published: February 2008

Measurements of nitric oxide (NO) and ozone (O3) in the free troposphere were made on board aircraft over the western Pacific Ocean during the period between March 7 and 10, 1989. The aircraft flew out from Narita (35°N) in Japan to Biak (1°S) in Indonesia along the longitude of 140° ± 5°E. The return flights from Biak were made at longitudes closer to the Asian continent ranging between 120° and 135°E. Both NO and O3 mixing ratios were observed to have pronounced latitudinal dependence. South of 6°N, very low NO and O3, with mixing ratios of about 7 parts per trillion by volume (pptv) and 14 parts per billion by volume (ppbv) respectively, were observed to prevail at a 4.5 km altitude. Near the latitude of 10° ± 3°N, NO and O3 showed a sharp increase toward the north, coinciding with a sharp fall in the dew point. North of 17°N, the median NO and ozone values in the continental airmass were 19 pptv and 50 ppbv, respectively, while corresponding values in maritime air mass were 21 pptv and 30 ppbv. These NO mixing ratios north of 17°N over the western Pacific Ocean are somewhat larger than the values obtained over the northeastern and north central Pacific Ocean probably due to a stronger influence of the outflow from east Asia on the western Pacific region. A pronounced peak in NO mixing ratio which reached 40 pptv was observed near 20°N which indicates more direct influences of anthropogenic NOx emissions from Asia.
The environmental history and probable future of fluorocarbon 11
Authors: Khalil M. A. K. , Rasmussen R. A.
Published: February 2008

The atmospheric concentration of fluorocarbon 11 (F‐11) has increased steadily since it was first put into commercial use in the late 1930s and early 1940s. The observed trends, however, have two periods of dramatic declines. The first occurred around 1974, when trends started falling from their all time high of 13.8 pptv/yr down to around 7.8 pptv/yr (1 pptv = 10−12 parts by volume) in 1982. This decline occurred at first, probably, because of market conditions and later because of the ban in the United States on inessential uses of F–11, particularly in aerosol spray cans. In the meantime, other uses of F–11, such as blowing foams, increased, causing an increasing trend once again until around 1987, when the atmospheric trends reached 11 pptv/yr (measured 1986–1988, inclusive). After this time, however, the trends have fallen dramatically and are now only 4.6 pptv/yr (measured 1990–1992) and even lower in the middle northern latitudes (about 2 pptv/yr). The recent decline of trend is attributed to the effect of the Montreal Protocol and subsequent agreements that are designed to ban worldwide production before the turn of this century. The atmospheric trends reflect estimated emissions, which reached highest values in 1974 (340–355 Gg/yr; 1 Gg = 109g) and again in 1988 (314–380 Gg/yr). The observed concentrations and trends agree extremely well with those calculated from independent estimates of emissions from the various sources. Atmospheric concentrations of F–11 are calculated from a mass balance theory involving seven reservoirs and their interactions. Three of the reservoirs are at the Earth's surface arising from the uses of F–11 (quick‐release applications such as open cell foams and aerosols, nonhermetically sealed refrigeration, and rigid polyurethane foams). We estimate that of the 9150 Gg of F–11 that have been produced throughout its history, at present about 1040 Gg are tied up in rigid foams (90 Gg and 24 Gg are tied up in refrigeration and quick‐release applications, respectively). There are four environmental reservoirs (deep oceans, the ocean mixed layer, the troposphere, and the stratosphere). F–11 is dynamically exchanged between these reservoirs and is destroyed principally by photolysis in the stratosphere and by soils at the Earth's surface. At present there are about 5360 Gg in the troposphere, 740 Gg in the stratosphere, and small amounts in the oceans (27 Gg and 6 Gg in the mixed layer and deep oceans, respectively). About 81% of the 9 Tg of F–11 produced is still in the surface or environmental reservoirs (1 Tg = 1012g). The future concentrations of F–11 depend on leakage rates from the surface reservoirs and the atmospheric lifetime. It seems that concentrations are not likely to reach the peaks expected earlier and are likely to decline faster than previously thought. The peak concentration is expected to be about 275 pptv and may occur within the next 2 to 3 years. This abstract, the figures, and their captions form a self‐contained condensed description of our results.
ATMOS/ATLAS 1 measurements of sulfur hexafluoride (SF6) in the lower stratosphere and upper troposphere
Authors: Rinsland C. P. , Gunson M. R. , Abrams M. C. , Lowes L. L. , Zander R. , Mahieu E.
Published: February 2008

Vertical profiles of sulfur hexafluoride (SF6) in the lower stratosphere and upper troposphere have been retrieved from 0.0l‐cm−1 resolution infrared solar occultation spectra recorded by the Atmospheric Trace Molecule Spectroscopy (ATMOS) Fourier transform spectrometer during the ATLAS (Atmospheric Laboratory for Applications and Science) 1 shuttle mission of March 24 to April 2, 1992. Based on measurements of the unresolved absorption by the SF6 ν3 band Q branch at 947.9 cm−1, average SF6 volume mixing ratios and 1‐sigma uncertainties of 3.20 ± 0.54 parts per trillion by volume (pptv; 10−12 ppv) at 200 mbar (∼11.8 km) declining to 2.86 ± 0.29 pptv at 100 mbar (∼16.2 km) and 1.95 ± 0.50 pptv at 30 mbar (∼23.9 km) have been retrieved. The profiles show no obvious dependence with latitude over the range of the measurements (eight occultations spanning 28°S to 54°S). Assuming an exponential growth model and applying a correction for the interhemispheric concentration difference, an average SF6 rate of increase of 8.7 ± 2.2% per year, 2 sigma, between 12 and 18 km has been derived by fitting the present measurements, ATMOS measurements from the April‐May 1985 Spacelab 3 mission, and balloon‐borne IR measurements obtained in March 1981 and June 1988.
Retrieval of stratospheric O3, HNO3 and ClONO2 profiles from 1992 MIPAS‐B limb emission spectra: Method, results, and error analysis
Authors: von Clarmann T. , Fischer H. , Friedl‐Vallon F. , Linden A. , Oelhaf H. , Piesch C. , Seefeldner M. , Völker W.
Published: February 2008

Within the framework of the European Arctic Stratospheric Ozone Experiment, two flights of the balloon‐borne MIPAS‐B limb emission spectrometer were performed in the Arctic stratosphere from Kiruna, northern Sweden. During the early hours of January 13 and the night from March 14 to March 15, 1992, several limb sequences of infrared spectra were recorded which have permitted the retrieval of vertical profiles of many trace gases relevant for ozone chemistry. In the present work, the retrieval strategy, error estimation strategy, and resulting profiles of O3, HNO3, and ClONO2 are reported. The data analysis procedure, consisting of data preprocessing including calibration, analysis of auxiliary data including temperature profiles and line of sight determination, and retrieval of trace gas profiles, is described in detail. The last is carried out by means of multiparameter nonlinear least squares fitting in combination with onion peeling. An astonishingly high ClONO2 amount of 2.6 ppb by volume at about 19‐km altitude was inferred for the March flight. A rigorous error analysis, which takes into account systematic and random errors and their often nonlinear impact on the results, proves the significance of the retrieved trace gas profiles.
High‐speed civil transport impact: Role of sulfate, nitric acid trihydrate, and ice aerosols studied with a two‐dimensional model including aerosol physics
Authors: Pitari G. , Rizi V. , Ricciardulli L. , Visconti G.
Published: February 2008

Recent assessment studies have shown that heterogeneous chemistry could have a significant role on the model‐predicted ozone changes due to gas injection from high‐speed civil transport (HSCT) aircraft. One major limitation of these numerical experiments was the highly simplified scheme adopted for the aerosol particles and, in particular, the absence of any explicit feedback between the gas phase chemistry included in the models and the total aerosol surface density available for heterogeneous reactions. In this paper we describe a two‐dimensional model covering the whole stratosphere and troposphere which includes photochemical reactions for the sulfur cycle and a microphysical code for sulfuric acid aerosols. Starting from these particles, the same code predicts also the size distribution for nitric acid trihydrate (NAT) and ice aerosols, covering globally a particle radius range between 0.01 μm and about 160 μm. A rather simple scheme is described for nucleation and condensation processes leading to the formation and growth of NAT and ice particles, still using grid point temperature data taken from the zonally averaged climatology of the lower stratosphere. A discussion is made of the HSCT impact on ozone adopting different scenarios for the aerosols. Model results for the aerosol size distribution and for the available surface densities appear reasonable when compared to satellite and balloon measurements and to independent numerical calculations. As pointed out also by previous research work and assessment panels, our calculation shows that the ozone sensitivity to HSCT emissions largely decreases when heterogeneous chemistry is included with respect to a pure gas phase chemistry case. In addition, our results indicate that the ozone sensitivity to HSCT emission decreases even more when NAT and ice aerosols are present: this is a consequence of the aerosol‐induced stratospheric denitrification which makes the residence time of the injected odd nitrogen shorter and the relative weight of the NOx catalytic cycle smaller. Inclusion of the sulfur dioxide feedback with the sulfate aerosol surface does not change significantly the ozone depletion in our model simulation, at least in the pure sulfate case. The additional ozone change due to aircraft injection of SO2 is larger when NAT and ice aerosols are allowed to form, due to the decreased ozone sensitivity to NOx. In this version of the model no direct aircraft emission of particulate has been included as a possible source for additional condensation nuclei.