bluuebunny/crossref_metadata_2025 huggingface dataset:
Forecasting Bering Sea ice edge behavior
Authors: Pritchard R. S. , Mueller A. C. , Hanzlick D. J. , Yang Y.‐S.
Published: February 2008

A coupled ice/ocean dynamics model is developed to provide Arctic offshore operators with 5‐ to 7‐day forecasts of ice motions, ice conditions, and ice edge motions. An adaptive grid is introduced to follow the ice edge, and the grid may move independently of the ice motion. The grid can be Lagrangian or Eulerian at different locations away from the ice edge. Ice stress is described using an elastic‐plastic model with strength determined by the ice conditions. The ocean dynamics model describes time‐dependent, three‐dimensional behavior, including wind‐driven currents and barotropic and baroclinic flows. The thermal energy budget of the ice cover is coupled to the ocean, with mass and salt interchange accompanying freezing or melting. Near the marginal ice zone (MIZ), surface winds (determined by reducing and turning the geostrophic winds) are enhanced to reflect observed behavior. The model was tested by simulating ice edge motions observed during the 1983 Marginal Ice Zone Experiment‐West and during drilling of the 1983 north Aleutian shelf Continental Offshore Stratigraphic Test well. Simulations of ice edge movement in the Bering Sea compare with observed data to within about 5 km/d. The model correctly describes mixed‐layer evolution in the marginal ice zone as fresh meltwater is mixed downward by turbulence. Along‐edge baroclinic flows due to density gradients across the ice edge are simulated by the model, in agreement with observations. Increased ice drift speeds generate higher melt rates due to increased turbulence levels, with the result that ice edge advance is moderated in spite of higher ice drift speeds.
Generation mechanism of internal waves by a vertically sheared tidal flow over a sill
Authors: Hibiya Toshiyuki
Published: February 2008

The internal response over a sill to strong tidal flow superimposed on a vertically sheared steady flow is examined with a simple two‐layer analytical model. As in the case where the vertical shear is absent, the upstream propagating internal wave is gradually formed through interference of infinitesimal‐amplitude internal waves (elementary waves) emanating from the sill at each instant of time (Hibiya, 1986); with the composite internal Froude number exceeding (falling below) unity in the accelerating (decelerating) stage of the two‐layer flow, the upstream propagating elementary waves come close together over the sill. In this case, however, the amplitude of the elementary wave is increased when the lower layer velocity is larger than the upper layer velocity, whereas it is reduced when the upper layer velocity is larger than the lower layer velocity. As a result, the internal wave field over the sill differs markedly between the ebb and flood tidal phases. It follows from this analytical result that in the Strait of Gibraltar, the internal wave propagating Mediterraneanward is significantly amplified during the ebb (westward) phase of the tidal flow, whereas such amplification does not take place throughout the tidal cycle for the internal wave propagating Atlanticward. This is consistent with the result from satellite observation that the sea surface signatures caused by underlying large‐amplitude internal wave trains appear only on the Mediterranean side and not on the Atlantic side.
Secular change of the seasonal variation in sea level and of the pole tide in the Baltic Sea
Authors: Ekman Martin , Stigebrandt Anders
Published: February 2008

Regular sea level observations have been performed in Stockholm since 1825, yielding the longest unbroken series of monthly mean sea levels in the world. Applying Fourier analysis to these data we have investigated the annual and semiannual sea level variations as well as the pole tide. Whereas the semiannual variation has a fairly constant amplitude of about 4 cm, the annual variation shows a secular increase in amplitude from 8 to 10 cm. This increase is statistically significant at the 99% level. It is suggested that this change might be connected to secular changes of the oceanographic conditions that have been observed to occur in the northeastern North Atlantic, especially a movement of the oceanic polar front. The pole tide also shows a secular change. The amplitude for the 14.3‐month Chandler period was less than 2 cm (below the noise level) during the previous century. During our own century the amplitude is 3 cm, 6 times the equilibrium tide. This might indicate that a meteorological forcing component close to the Chandler period has changed and added variability to the sea level at this period.
Observations on a bottom vein of dense water in the southern Adriatic and Ionian seas
Authors: Bignami Francesco , Salusti Ettore , Schiarini Silvia
Published: February 2008

We discuss the motion and spreading of a bottom vein of very dense marine water, which originates (σ ≥ 29.4) in winter through cooling and evaporation processes resulting from the violet Bora wind blowing over the shallow North Adriatic Sea into the deepest layers of the southern Adriatic and Ionian seas (eastern Mediterranean basin). Our analysis is focused on the peculiar physical processes that control this bottom flow. We first describe the vein motion in the southern Adriatic Sea in which this current follows approximately the isobaths (in partial accordance with the conservation of potential vorticity) and the main mixing process of dense water with Levantine Intermediate Water occurring in an offshore‐oriented canyon near Bari. This canyon causes a deepening and flattening of the original vein of dense water, such that downstream the water can be observed only on the Otranto Sill (at depths of ≈ 800 m with σ ≈ 29.25). The subsequent flow in the Ionian Sea follows approximately the 900‐m isobath in the Gulf of Taranto and along the Calabrian and east Sicilian coasts, in agreement with the results of Smith's and Killworth's theoretical models of steady motion of density driven currents over a regular slope, in a rotating system, for stratified fluids.
Effect of wave‐current interaction on wind‐driven circulation in narrow, shallow embayments
Authors: Signell R. P. , Beardsley R. C. , Graber H. C. , Capotondi A.
Published: February 2008

The effect of wind waves on the steady wind‐driven circulation in a narrow, shallow bay is investigated with a two‐dimensional (y, z) circulation model and the Grant and Madsen [1979] bottom‐boundary layer model, which includes wave‐current interaction. A constant wind stress is applied in the along‐channel x direction to a channel with a constant cross‐sectional profile h(y). The wind‐induced flushing of shallow bays is shown to be sensitive to both the shape of the cross section and the effects of surface waves. The flushing increases with increasing
, where h′ is the standard deviation of cross‐channel depth and
is the mean depth. This is consistent with the findings of Hearn et al. [1987]. The flushing decreases, however, with the inclusion of surface wave effects which act to increase the bottom drag felt by the currents. Increasing effective bottom friction reduces the strength of the circulation, while the along‐bay surface slope, bottom stress and the structure of current profiles remain nearly unchanged. An implication of the circulation dependence on wave‐current interaction is that low‐frequency oscillatory winds may drive a mean circulation when the wave field changes with wind direction.
Dissolution of 100 to 1000 μm diameter air bubbles in reagent grade water and seawater
Authors: Detsch Richard M.
Published: February 2008

The dissolution of freely rising, 100 to 1000 μm diameter air bubbles was measured in reagent grade water, seawater, and artificial seawater. Dissolution was studied for samples having varied percent air saturation, and temperature. All data were taken at atmospheric pressure. Bubbles dissolved faster in water and artificial seawater than in seawater and there is less scatter in the dissolution data for water than for seawater. The dissolution rate is linearly dependent on percent air saturation and is independent of diameter. Dissolution was measured at several temperatures between 6°C and 44°C in seawater and is weakly dependent on temperature within this range. The data are in good agreement with theory. Comparison with earlier seawater data taken at higher pressures indicates that a mechanism for inhibiting dissolution is present at high pressures.
Observations of the Niagara River thermal plume (Lake Ontario, North America)
Authors: Masse Ann K. , Murthy C. R.
Published: February 2008

Temperature and velocity data are used to describe the Niagara River discharge into Lake Ontario between April and November 1982. The Niagara River discharge (7000 m3 s−1) is usually slightly warmer and therefore less dense than the ambient lake surface water. The density difference varies throughout the year, with the largest density difference being measured in October. Near the river mouth, where the fluid speeds are roughly 1 m s−1, the plume is vertically homogeneous. Here advective forces dominate the momentum balance, even in the presence of strong wind forcing. Approximately 5 km offshore the plume separates from the lake bottom as the water depth increases and buoyancy forces become important. At the offshore boundary of the plume, advection, Coriolis force, buoyancy, and wind stress are all important. The Coriolis effect acts to turn the plume anticyclonically and form a right‐bounded coastal current with speeds of 0.1–0.2 m s−1. Strong upwelling‐favorable winds force the buoyant plume to spread offshore, thinning the plume as it spreads. Eventually, the plume water is mixed with the lake water by the wind. Strong downwelling‐favorable winds concentrate the plume into a narrow and deep coastal current traveling downwind with the coast on its right. Thus exchange between the plume and the lake is enhanced by upwelling‐favorable winds and inhibited by downwelling‐favorable winds.
Interpreting shear and strain fine structure from a neutrally buoyant float
Authors: Kunze Eric , Briscoe Melbourne G. , Williams A. J.
Published: February 2008

The 1–5 m shear and strain spectra from a neutrally buoyant float reveal more strain in the near‐inertial band (f < ω < 2f ∼ M2) and more shear in the continuum internal wave band (2f < ω < N) than can be accounted for by linear internal gravity waves. The shape of the 1‐m shear spectrum can be reproduced by vertically advecting low‐frequency ∼2‐m wavelength fine structure past the float sensors with the observed displacement time series. Advection smears the encounter frequency across the internal wave band, aliasing and Doppler shifting some low intrinsic frequency variance into the continuum band and some high intrinsic frequency wave variance into the near‐inertial band. Past observations of the excess shear variance at high frequencies led to speculation that it may be stratified two‐dimensional turbulence having the same spatial scales as internal waves but carrying fine‐scale potential vorticity anomalies (Holloway, 1983). The high shear relative to strain (Vz/(
ζz) = 2.2) and high Froude number (Vz/
= 1.23) would restrict stratified two‐dimensional turbulence to having average relative vorticity more negative than −f. This limitation makes a stratified turbulence explanation for the fine structure impossible. On the other hand, the shear and strain characteristics are consistent with the Garrett and Munk (1979) internal wave model and could easily be explained by near‐inertial internal waves. There may be no efficient means of generating potential vorticity anomalies away from boundaries.
Effects of cloudiness on the atmospherics level during the SW monsoon season
Authors: Bhattacharya A. B. , Chakraborti A. K. , Bhattacharya R.
Published: February 2008

It is shown that the occurrence of different monsoon cloud amounts is closely associated with the integrated field intensity of atmospherics simultaneously recorded over Calcutta at 10, 20, and 30kHz. Some of the interesting results achieved from an analysis of the observations during the monsoons of 1977 to 1979 are reported here, and the results are critically discussed in light of the present knowledge of monsoon characteristics.
Intercomparison of the NIMBUS 7 SBUV/TOMS total ozone data sets with Dobson and M83 results
Authors: Bhartia P. K. , Klenk K. F. , Wong C. K. , Gordon D. , Fleig A. J.
Published: February 2008

Total ozone measurements made by the SBUV and TOMS instruments on the NIMBUS 7 spacecraft are compared with measurements from 62 Dobson and 18 M83 stations. On the average, TOMS ozone values are 6.6% smaller than Dobson and 9.1% smaller than M83; corresponding SBUV biases are 8.3% and 11.3%, respectively. Use of SBUV or TOMS as a transfer standard reveals an apparent bias between the Dobson and M83 networks of 3.0 or 2.5%respectively. Major portion of the bias between the space and ground measurements is attributed to uncertainties in the ozone absorption coefficients used in processing the measurements. Precision of total ozone retrieved from either the SBUV or the TOMS instrument is shown to be better than 2%, which is comparable to that of a well run Dobson station. Precision of a typical Dobson measurement is estimated at about 2% and that of an M83 measurement is estimated to be 4%. Apparent station to station biases of up to 11.2% for Dobson and 15.5% for M83 are shown. Daily and seasonal variations of ozone measured by the satellite over selected Dobson stations are found to be in excellent agreement with the ground observations. An instrumental drift is found in the SBUV/TOMS total ozone measurements that is essentially linear with time and has a rate of 0.5% per year for the first year of data. A better understanding of instrument changes is expected to help reduce any further drift.
Thundercloud current determination from measurements at the Earth's surface
Authors: Nisbet John S.
Published: February 2008

The information that can be obtained about the locations and the magnitudes of currents into active centers in a thundercloud from current density and electric field measurements at the surface of the earth below the cloud are examined. A dynamic interactive electrical model has been used in which the distributed earth, atmosphere, ionosphere circuit is included. In the model, electrification mechanisms in the cloud are simulated by generators; conduction and displacement currents flow in resistors and capacitors between nodes at grid points. Lightning is simulated by switches which drastically reduce the resistances between nodes when the electric field exceeds an assumed breakdown value and raise them again when they drop below the value assumed necessary to sustain the arc. The technique allows the divergence of the Maxwell current to be kept zero everywhere. The effects of the intensity and geometry of the generators, the conductivity and conductivity gradient in the cloud, and of the exchange layer and coronal ions are investigated at times when the configurations are reasonably constant, as well as at the beginning and end of a storm. It is shown that the current densities to the ground between lightning discharges provide a good measure of the generator current system associated with the cloud and that their time variations after flashes provide information on the altitude profile of the conductivity. As an example of the application of the technique, the currents under a small Florida thunderstorm are analyzed after a cloud‐ground discharge.
Ion‐aerosol attachment coefficients, ion depletion, and the charge distribution on aerosols
Authors: Hoppel William A.
Published: February 2008

Calculations of the ion‐aerosol attachment coefficients are carried out for particles with radii between 0.001 and 4 μm in a bipolar ion environment by using the theory (Hoppel, 1977) that includes both image capture and three‐body trapping of ions. These attachment coefficients are used to calculate the equilibrium charge distribution on aerosols. The results are compared to Fuchs' theory and to several recent measurements of the equilibrium charge distribution. The experimentally measured charge distributions agree quite well with theory. Recent measurements of aerosol size distributions made with the differential mobility size spectrometer in both continental and oceanic atmospheres are used together with the calculated attachment coefficients to study the sensitivity of the atmospheric ion concentration on the aerosol size distribution.
Identification of 18O‐isotopic lines of ozone in infrared ground‐based solar absorption spectra
Authors: Rinsland C. P. , Devi V. Malathy , Flaud J.‐M. , Camy‐Peyret C. , Smith M. A. H. , Stokes G. M.
Published: February 2008

A number of relatively well‐isolated lines of the v3 bands of 16O18O16O and 16O16O18O have been identified in high‐resolution solar absorption spectra recorded with the Fourier transform interferometer at the National Solar Observatory on Kitt Peak (elevation 2095 m, latitude 31.9°N). Based on spectroscopic parameters derived from ozone laboratory spectra recorded with the same instrument, the heavy ozone content of the total column of ozone has been determined from measurements of the equivalent widths of 16O18O16O, 16O16O18O, and 16O3 lines in three solar absorption spectra. Relative to the concentrations in a natural sample of ozone, the analysis indicates 16O18O16O and 16O16O18O isotopic abundances of 1.05±0.07 and 1.11±0.11 in the total column of atmospheric ozone.
Volcanic deposits in Antarctic snow and ice
Authors: Delmas Robert J. , Legrand Michel , Aristarain Alberto J. , Zanolini Françoise
Published: February 2008

Major volcanic eruptions are able to spread large amounts of sulfuric acid all over the world. Acid layers of volcanic origin were detected for the first time a few years ago by Hammer in Greenland ice. The present paper deals with volcanic deposits in the Antarctic. The different methods that can be used to find volcanic acid deposits in snow and ice cores are compared: electrical conductivity, sulfate, and acidity measurements. Numerous snow and ice samples collected at several Antarctic locations were analyzed. The results reveal that the two major volcanic events recorded by H2SO4, fallout in Antarctic ice over the last century are the eruptions of Krakatoa (1883) and Agung (1963), both located at equatorial latitudes in the southern hemisphere. The volcanic signals are found to be particularly well defined at central Antarctic locations apparently in relation to the low snow accumulation rates in these areas. It is demonstrated that volcanic sulfuric acid in snow is not even partially neutralized by ammonia. The possible influence of Antarctic volcanic activity on snow chemistry is also discussed, using the three recent eruptions of the Deception Island volcano as examples. Only one of them seems to have had a significant effect on the chemistry of snow at a location 200 km from this volcano. It is concluded that Antarctic volcanic ice records are less complicated than Greenland records because of the limited number of volcanos in the southern hemisphere and the apparently higher signal to background ratio for acidity in Antarctica than in Greenland.
The solar and dynamically induced oscillations in the stratosphere
Authors: Chandra S.
Published: February 2008

The temporal and spatial characteristics of short‐term fluctuations in the stratosphere are studied using 30 months of ozone, solar UV, and temperature data from the Nimbus 7 solar backscattered ultraviolet (SBUV) and the stratosphere and mesosphere sounder (SAMS) experiments. It is shown that the stratosphere is in a continuous state of oscillation, with periods varying between 3 to 7 weeks. These oscillations are manifestations of dynamically induced perturbations in the winter hemisphere and the 27‐day modulation of the solar UV radiation. Dynamically induced oscillations are global in extent and appear to be independent of solar activity. They are strongest at high latitudes during the fall‐spring epoch of each hemisphere. When the seasonal differences of the two hemispheres are taken into account, the high‐latitude oscillations in each hemisphere show significant negative correlation with lower latitudes which extends far beyond the tropics into the opposite hemisphere. Their phase shows the characteristics of meridional waves with poleward and equatorward propagations above and below 10 mbar, respectively. Both the multiple regression and cross‐spectral analyses of ozone, temperature, and solar flux data show the ozone mixing ratio to be much more sensitive to dynamically induced changes in temperature than to changes in solar UV flux. The solar‐induced changes in ozone are detectable only under favorable circumstances, that is, at low latitudes during periods of high solar activity. The estimated change in ozone mixing ratio in the upper stratosphere is about 3% over a solar cycle. This is comparable to a temperature‐induced change of about 2 K of dynamical origin.
Theoretical analysis of isotope effects on ozone formation in oxygen photochemistry
Authors: Kaye Jack A.
Published: February 2008

In situ measurements of stratospheric ozone and laboratory studies of ozone production in electric discharge through oxygen have shown previously that ozone containing heavy isotopes of oxygen (17O, 18O) may be formed preferentially. In order to assess the relevance of the latter experiment to the stratospheric measurements, detailed understanding of the effect of isotopic substitution on the O3 formation reaction O + O2 + M → O3 + M and on the O atom exchange reaction O + O2 → O2 + O is necessary. In this work, an estimate of the effect of isotopic substitution on the recombination rate is made by use of approximate dynamical theories and statistical mechanics. The results indicate the possibility of isotope effects on the O + O2 recombination rate of the order of several percent at stratospheric temperatures. In general, recombination reactions involving heavy (mass 49, 50) O3 formation are found to be slower than the reaction leading to normal (mass 48) O3 formation. The calculated isotope effects are sufficiently small that the uncertainties in the model input and the approximations in the dynamical theories will probably make the quantitative nature of these results subject to considerable uncertainty. This isotope effect should not be observable in the atmosphere given the precision of the current measurements but may be crucial in the understanding of the laboratory experiments, where observed enhancements are only of the order of several percent. Possible reasons for this discrepancy between the observed enhancement and predicted depletion are presented.
Seasonal variations of tropospheric ozone at Natal, Brazil
Authors: Logan Jennifer A. , Kirchhoff Volker W. J. H.
Published: February 2008

We present an analysis of ozone measurements from Natal, Brazil (6°S, 35°W), with a focus on the seasonal behavior in the troposphere. The amplitude of the seasonal cycle at Natal is much larger than at Panama (9°N), the only other tropical site for which similar data are available. Concentrations of ozone in the middle troposphere in the southern spring are unexpectedly high, 60–70 ppb, similar to values found at northern mid‐latitudes in summer, and larger by 20–30 ppb than values found at Panama and at southern mid‐latitudes. We suggest that photochemical production of ozone associated with emissions of CO, hydrocarbons, and NOx from biomass burning may contribute significantly to the high values of ozone, but note that stratospheric intrusions could also play a role. The data available at present do not permit a definitive evaluation of the relative importance of these two sources of ozone. The data from Natal, in combination with recent aircraft and surface data, show that tropical ozone exhibits strong spatial and temporal inhomogeneities. The distribution of tropospheric ozone appears to be considerably more complex than the traditional view, which suggested a northern midlatitude maximum, and north/‐south hemispheric asymmetry. The seasonal cycle in the total column of ozone at Natal appears to mirror the behavior of the tropospheric contribution to the ozone column rather than the stratospheric contribution, and this may account for differences in the annual cycle of the total column at Natal versus other tropical locations.
Airborne intercomparison of carbon monoxide measurement techniques
Authors: Hoell James M. , Gregory Gerald L. , McDougal David S. , Sachse Glen W. , Hill Gerald F. , Condon Estelle P. , Rasmussen Reinhold A.
Published: February 2008

Results from an airborne intercomparison of techniques to measure tropospheric levels of carbon monoxide (CO) are discussed. The intercomparison was conducted as part of the National Aeronautics and Space Administration's Global Tropospheric Experiment and included a laser differential absorption method and two grab sample/gas chromatograph methods. Measurements were obtained during approximately 90 flight hours, during which the CO mixing ratios ranged from about 60 to 140 ppbv. The level of agreement observed for the ensemble of measurements was well within the overall accuracy stated for each instrument. The correlation observed between the measurements from the respective pairs of instruments ranged from 0.85 to 0.98, with no evidence for the presence of either a constant or proportional bias between any of the instruments.
Surface‐observed and satellite‐retrieved cloudiness compared for the 1983 ISCCP Special Study Area in Europe
Authors: Henderson‐Sellers A. , Séze G. , Drake F. , Desbois M.
Published: February 2008

A comparison has been undertaken between surface‐observed total low‐ and high‐cloud amount and retrievals from METEOSAT radiance data made using the cluster technique of Desbois et al. (1982). The aim of the study was to establish whether surface‐observed cloud information could be usefully exploited to benefit satellite‐based cloud retrievals. Observations from 124 surface stations at 1200 UT for the 20‐day period from July 22 to August 10, 1983, were compared with retrievals made from METEOSAT radiances measured at 1130 UT. The comparisons for total and low‐cloud amount are made for France and southern Britain. The high‐cloud amount comparison was limited to 34 stations in southern Britain. The location and time period were selected to coincide with one of the regions designated for special study in the International Satellite Cloud Climatology Project (ISCCP) (Schiffer, 1982). For total cloud amount, 29% of the retrievals were fully in agreement with the surface observations and 64% of differences were within ±1 okta (±1 eighth of sky cover). In the case of layer cloud amounts, 64% of the low‐cloud amount differences and 50% of the high‐cloud amount differences were within ±1 okta, although many of these successes (71% in the low‐cloud amount) were for cases of totally clear or totally cloudy skies. Surface observations, which offer the only source of accurate low‐cloud amount evaluation in any multilayered situation, were found to identify thin cirrus which was not detected by the satellite retrieval and to detect small gaps in cloud decks and small clouds missed by the satellite retrieval. In addition, cloud retrievals in coastal locations seemed to be more successfully accomplished by surface observers than by the satellite retrieval algorithm used here, which does not take into account land‐sea partition.
Comparison of Nimbus 7 wide‐angle earth radiation budget measurements with the output of four cloud‐generating numerical climate models
Authors: Paltridge Garth W.
Published: February 2008

A preliminary “first‐order” comparison is performed between Earth Radiation Budget (ERB) global data sets from four different cloud‐generating climate models and the 5‐year averages of Nimbus 7 wide‐angle measurements of ERB for December and June. The rms differences between the model fields and the Nimbus averages are of the order of 1.5–2 times the rms interannual variability of the Nimbus measurements themselves (which are roughly 10 W m−2 for long‐wave and 25 W m−2 for shortwave). Correlations between model and measurement on a regional scale are not obvious. A more direct comparison with the Nimbus measurements of model ERB calculated at the time of the satellite overpass gives very large rms differences, which presumably are a reflection of inherent noisiness of the model calculations. It is recommended for the future that for purposes of tuning models, the calculated outputs be of the fluxes at satellite height and position. They should also be in a common agreed format.
The potential impact on atmospheric ozone and temperature of increasing trace gas concentrations
Authors: Brasseur Guy , De Rudder Anne
Published: February 2008

The response of the atmosphere to emissions of chlorofluorocarbons (CFCs) and other chlorocarbons and to increasing concentrations of other radiatively active trace gases such as CO2, CH4, and N2O is calculated by means of a coupled chemical‐radiative‐transport one‐dimensional model. It is shown that significant reductions in the ozone concentration and in the temperature should be expected in the upper stratosphere as a result essentially of increasing concentrations of active chlorine produced by photo decomposition of the CFCs. For a constant emission of chlorofluorocarbons‐11 and ‐12 at approximately the 1980 level (309 kT/yr for F‐11 and 433 kT/yr for F‐12) the calculated decrease (assuming no other changes) in the ozone concentration relative to the preindustrial atmosphere is approximately 60–70% at 40 km, and the reduction in the ozone column is 8.7% when temperature feedback is included in the model and 5.5% when it is omitted. The model also shows that a doubling of CO2 leads to a 1.8% increase in the ozone column abundance and a 2 K increase in the surface temperature. At 40 km the ozone density is enhanced by 15% and the temperature reduced by 8 K. A doubling of methane produces a 2.4% increase in the ozone column. A 20% enhancement in the nitrous oxide content leads to an ozone depletion of 1.4%. Time‐dependent calculations of ozone and temperature show that if the production of F‐11 and F‐12 increases by 3%/yr until it reaches a capacity cap equal to 1.5 times the 1985 world production level, the maximum ozone depletion should be of the order of 4–5%, assuming a growth in the concentration of CO2, CH4, and N2O of about 0.5, 1.0, and 0.25%/yr, respectively. For this scenario the maximum ozone depletion is found to occur in year 2070. The slight increase appearing after 2070 is directly dependent on the future growth in the methane concentration. If the production of F–11 and F–12 increases continuously by 3%/yr, without capacity cap, and if the changes in the concentration of other trace gases are ignored, the ozone column abundance is predicted to be reduced by more than 10% after year 2050. The model shows an almost linear relation between the ozone depletion and the chlorine content as long as the mixing ratio of active chlorine remains smaller than that of active nitrogen. The O3/Clx sensitivity, however, is a strong function of NOy content. For amounts of chlorine comparable or larger than those of active nitrogen the ozone depletion increases rapidly with the amount of chlorine present in the atmosphere.
A saturated inertia gravity wave in the mesosphere observed by the middle and upper atmosphere radar
Authors: Yamamoto Mamoru , Tsuda Toshitaka , Kato Susumu , Sato Toru , Fukao Shoichiro
Published: February 2008

We have found the dominance of a monochromatic inertia gravity wave with a vertical wavelength of approximately 5.6 km from middle and upper atmosphere radar observations of the mesosphere on February 8, 1985. By assuming linear dispersion and polarization equations for gravity waves, we have estimated the intrinsic period and propagation direction of the wave as 8 hours and northward, respectively. The minimum Richardson number for the atmosphere as modified by the inertia gravity wave was slightly negative near 72 km, which implies that the wave was saturated and generated turbulence through shear and convective instabilities. We observed an echo power enhancement near the altitude of the minimum Richardson number. At 68–78 km altitude we found intermittent fluctuations in radial wind velocities with a period of 9 min. Their phases rapidly reversed near 73 km, where their amplitudes reached a minimum and the Richardson number was less than 1. These fluctuations seem to be attributable to the shear or convective instabilities generated by the saturating gravity wave.
Regional aerosol chemistry of the Amazon Basin during the dry season
Authors: Talbot R. W. , Andreae M. O. , Andreae T. W. , Harriss R. C.
Published: February 2008

We report here a set of measurements which describe the distribution and chemical composition of the atmospheric aerosol over the tropical rain forest of the Amazon Basin, in Brazil, during the 1985 July–August dry season. Our data suggest that there is remarkable compositional and spatial homogeneity of the atmospheric aerosol on an extensive regional scale. We describe the aerosol regime associated with emissions from the moist tropical forest during early to middle dry season conditions. The moist forest ecosystem is a source of aerosols, composed of material directly released by vegetation, together with species originating from biogenic emissions of various reduced atmospheric gases. Particulate organic carbon is the dominant component of the atmospheric aerosol, exhibiting an average concentration of 740±190 nmol C m−3 in the mixed layer and 220±60 nmol C m−3 in free tropospheric air. On the average the atmospheric concentration of aerosol constituents was enhanced in mixed layer air fivefold over free tropospheric levels. Oxalate and SO42− exhibited the greatest enrichment in the mixed layer, while Cl− showed essentially no enrichment in mixed layer aerosols. For many constituents their enhancement in mixed layer air was greatest in the aerosol coarse fraction, exceeding a factor of 10 in some cases. Approximately 75% of total aerosol NO3− in the mixed layer was contained in the coarse atmospheric aerosol. The atmospheric aerosol in the Amazonian atmosphere is essentially acid‐base neutral, primarily as a result of incorporation Of NH4+, presumably derived from NH3 released by the forest ecosystem. Ammonium ion is the principal ionic constituent of the atmospheric aerosol, being present at a concentration typically more than twice that of other major ionic species. The biospheric‐atmospheric coupling of emissions of NH3 and reduced sulfur gases by the forest ecosystem, and subsequent incorporation of atmospheric NH3 into acidic aerosols produced by oxidation of reduced atmospheric sulfur gases, is an important aspect of biogeochemical cycling to be pursued in future studies.
Comparison of model‐generated and satellite‐derived cloud cover and radiation budget
Authors: Buriez J.‐C. , Bonnel B. , Fouquart Y. , Geleyn J.‐F. , Morcrette J.‐J.
Published: February 2008

Using a data set including large‐scale fields and collocated satellite observations (the NEPHOS file), we test the validity of the approach proposed for validating general circulation model type cloud schemes with the future International Satellite Cloud Climatology Project (ISCCP) and First ISCCP Regional Experiment (FIRE) data sets. An ensemble of 2866 atmospheric situations extracted from the NEPHOS file is used to test the European Center for Medium Range Weather Forecasts operational cloud cover scheme and to study the sensitivity to cloud cover of the regional radiation budget over the eastern Atlantic Ocean and the North Sea. This scheme, based on a simple function of the relative humidity, is shown to underestimate the cloud cover (by 26%), especially when stratocumulus clouds are present. This underestimation is related to too small values of the analyzed relative humidity in the model's planetary boundary layer. The vertical gradient of potential temperature is shown to be a better predictor for this low‐level cloudiness. Differences between the observed and generated radiation budget at the top of the atmosphere are induced by the differences in cloud cover. However, differences in the cloud radiative properties introduce some compensating effects, and the mean bias error is only +7 Wm −2. Particularly, the mean value of the shortwave albedo is too high in the model, and its variation as a function of the cloud cover is much too smooth, as the model does not account for the observed increase in the vertical optical depth of clouds when the cloud cover increases.
Application of sensitivity and uncertainty analysis techniques to a photochemical ozone model
Authors: Derwent Richard , Hov Øystein
Published: February 2008

By means of life cycle modeling and Latin hypercube sampling, uncertainties in ozone concentrations downwind of London have been estimated for the first time in photochemical models, albeit with the involvement of a substantial element of subjective judgement. The analysis has led to a clear definition of which areas of model input determine the greatest contribution to the uncertainties in the calculated distribution of a wide range of secondary pollutants generated downwind of London. These calculations show that the initial concentrations of hydrocarbon emissions are heavily dominated by uncertainties in wind speed, photolysis rates, and hydroxyl radical sinks. Each secondary pollutant is influenced to different extents by the different model input areas. However, when ozone control strategies are evaluated, these uncertainties are no longer significant, and other parameters dominate. Accurate prediction of ozone concentrations at a specific location does not necessarily guarantee accurate prediction of the model responses to ozone control strategies.
On the meridional structure of long‐lived tropospheric constituents
Authors: Plumb R. Alan , McConalogue Denis D.
Published: February 2008

We consider the general problem of the meridional distribution and seasonal variability of long‐lived atmospheric constituents. Here “long‐lived” means that the time scale of the constituent exceeds the atmospheric exchange time across the region of interest. The relevant time scale is the “dynamic lifetime,” defined here as the ratio of the total atmospheric loading of the constituent to the total global source. Provided that this quantity is large (greater than about 5 years for the troposphere), the constituent attains a “gradient equilibrium” in which spatial gradients of mixing ratio are weak and the meridional and seasonal structure take on a form which, for a given source, is independent of the dynamic lifetime. Analysis of this structure involves clarification of the nature of atmospheric exchange processes and leads us to highlight thé nonuniqueness of such concepts as “interhemispheric exchange times.” These results are illustrated using a two‐dimensional transport model to conduct simulations of idealized long‐lived constituents with, in most cases, a simple mid‐latitude northern hemisphere source and a sink with uniform decay rate. It is suggested that these results will aid the synthesis of observations of long‐lived tropospheric constituents and will simplify the validation of transport models. More generally, this kind of approach might help to identify the effects of transport on trace constituent structures and thereby contribute to the understanding of the distributions of constituents which are not “long‐lived” in the sense used here.
Kinetics of aqueous phase reactions of the SO4−radical with potential importance in cloud chemistry
Authors: Wine P. H. , Tang Y. , Thorn R. P. , Wells J. R. , Davis D. D.
Published: February 2008

A laser flash photolysis/long path absorption technique has been employed to study at 298 K the kinetics of aqueous phase reactions of the SO4−radical with a number of species commonly found in cloud water. Much lower radical concentrations were employed than in all previous direct studies of SO4−reaction kinetics. In the zero ionic strength limit, rate coefficients for SO4−reactions with the anions HSO3−, Cl−, NO2−, HCOO−, and CH3COO−are found to be 7.5 × 108, 2.6 × 108, 9.8 × 108, 1.1 × 108, and 3.7 × 106M−1s−1, respectively. Rate coefficients for SO4−reactions with the neutral species H2O2, CH3OH, HCOOH, and CH3COOH are found to be 1.2 × 107, 8.8 × 106, 4.6 × 105, and 1.4 × 104M−1s−1, respectively. For many of the reactions studied, agreement with previously reported rate data is poor. Of particular importance for cloud chemistry is the fact that the SO4−+ HSO3−reaction proceeds more slowly than previously believed, while the SO4−+ Cl−reaction is somewhat faster than previously thought. Incorporation of these results into cloud chemistry models should reduce the calculated efficiency of free radical chain reactions as an oxidation mechanism for S IV.
Natural and transmission line produced positive ions
Authors: Eisele F. L.
Published: February 2008

Positive ions were studied at three field sites, two of which contained ions produced by high‐voltage direct current (HVDC) transmission lines. Natural ions were also studied at two of the three sites. The observed differences between natural and anthropogenic ion spectra near HVDC lines are attributed primarily to a shortening of ion lifetimes by the strong electric field associated with the HVDC lines. One exception is the production of potassium‐ and probably sodium‐based ions from the decomposition of insects in transmission line coronas. Several ions which have been observed previously at mass 60 and 130 were also identified for the first time, using tandem mass spectrometric techniques, as trimethylamine and quinoline (and isoquinoline), respectively.
Nonmigrating thermal tides detected in data analysis and a general circulation model simulation
Authors: Yagai Isamu
Published: February 2008

Nonmigrating thermal tides, which do not move in synchrony with the Sun, are detected in the analyses of the First GARP Global Experiment (FGGE) Level IIIb data during the special observation period (SOP‐1) of January 10, to February 9, 1979. The first is the westward moving diurnal mode, with the zonal wave number (m) 5 (f = −1, m = 5), and the second is an eastward moving diurnal mode, with the zonal wave number 3 (f = 1, m = 3), where f is the frequency in day−1. These modes are closely related to wave number 4 of the topography at low latitudes and have clear peaks in the space‐time power spectra in the sea level pressure field. A maximum value of 0.2 mbar is the same with both modes, as expected from theory, while maximum values of the background diurnal (f = −1, m = 1) and semidiurnal (f = −2, m = 2) migrating modes are 0.6 and 1.2 mbar, respectively. These nonmigrating modes are essentially the same ones that Tokioka and Yagai [1987] reported in their analysis of general circulation model (GCM) simulation in January. By comparing FGGE IIIb data analysis and the Meteorological Research Institute (MRI) GCM‐I simulation, diurnal (f = −1, m = 1) and semidiurnal (f = −2, m = 2) modes are simulated well in the sea level pressure field and relatively well at the lower troposphere in the geopotential field. The simulated nonmigrating modes have horizontal structures similar to those observed in the sea level pressure field, which are the most reliable data and are based on a large enough number of observations to detect these modes. In the geopotential field, horizontal structure of the nonmigrating modes is identified in the troposphere at low latitudes by simulation and observation. The wind data is also analyzed, but the correspondence between the simulation and observation is found only at the lowest level of the (f = −1, m = 5) mode.
The sensitivity of total ozone and ozone perturbation scenarios in a two‐dimensional model due to dynamical inputs
Authors: Jackman Charles H. , Douglass Anne R. , Guthrie Paul D. , Stolarski Richard S.
Published: February 2008

The sensitivity of the total ozone distribution in our two‐dimensional photochemical model to dynamical inputs has been explored. The residual circulation has been computed from three sets of heating rates but using the same temperature distributions. These heating rates result in advection fields that are appropriately linked with the magnitude of their vertical winds in the lower stratosphere and are called: (1) the strong circulation, (2) the weak circulation, and (3) the combined circulation. Three different formulations of horizontal eddy diffusion have also been investigated, including (1) a small constant diffusion, (2) a computed diffusion from potential vorticity using measured temperatures, and (3) a self‐consistent diffusion determined from the meridional velocity. Finally, we studied two different formulations of vertical eddy diffusion: (1) a small constant diffusion and (2) an altitude‐dependent larger diffusion. Our modeled global average total ozone varies by up to 10%, depending on the various dynamical inputs, and the seasonal and latitudinal variabilities are even more substantial. The calculations indicate that total ozone in the middle to high latitudes is very sensitive to the advection field below 100 mbar, the region where the heating rates (which are used in computing the advection field) are most uncertain. Modeled total ozone shows better agreement with solar backscattered ultraviolet (SBUV) ozone climatology, when computed horizontal eddy diffusion is used. Our “best” modeled total ozone distribution is a result of using the heating rates from Rosenfield et al. (1987) for pressures less than 100 mbar, along with heating rates from Dopplick (1974, 1979) for pressures greater than 100 mbar. Our model results, especially when comparing model and SBUV ozone between 10 and 1 mbar, indicate that there is an inconsistency between our “best” horizontal eddy diffusion and the “best” mean residual circulation. Our studies indicate a relative similarity of a typical ozone perturbation scenario among the different dynamical inputs. All of the perturbation studies predict the smallest ozone changes in the tropical latitudes, with larger ozone changes in the middle to high latitudes. The major changes in the various perturbation results are in the middle to high latitudes: (1) the peak ozone change is off of the pole in the southern hemisphere (near 60°S latitude) using the strong circulation but centered on the pole for the various other dynamical studies, and (2) the maximum ozone change is centered at times varying from early spring to early summer, depending on which dynamical input is used.
Regional contributions to the atmospheric excitation of rapid polar motions
Authors: Salstein David A. , Rosen Richard D.
Published: February 2008

Daily fields of surface pressure produced by the National Meteorological Center during 1981–1985 are used to identify the sectors of the globe over which changes in atmospheric mass contribute most importantly to the excitation of intraseasonal variations in the Earth's polar axis. Maxima in the excitation function are found over the extratropical South Pacific, North Pacific, and North Atlantic, consistent with previous studies that have identified maxima in surface pressure variations in these regions. Because these centers are located over the ocean, the manner in which the ocean responds to changes in the atmospheric mass above it becomes of central importance in fully understanding the causes of rapid polar motions.