bluuebunny/crossref_metadata_2025 huggingface dataset:
Submicron film drop production by bubbles in seawater
Authors: Resch François , Afeti George
Published: February 2008

The marine droplet aerosol, composed of the film and jet drops produced by breaking bubbles, is at the origin of most of the sea salt particles found in the atmosphere. For a long time, it was believed that the number of film drops produced per bubble burst increased continuously with increasing bubble diameter. Recently, however, Blanchard and Syzdek (1988) reported a peak in film drop production in the bubble size range of 2‐ to 2.5‐mm diameter, with much lower drop counts for larger bubbles. Experiments designed to investigate this peak over the bubble diameter range of 1.06–5.7 mm are reported. The results confirm the existence of a peak in the film drop count data at a bubble diameter of about 2.14 mm. The size distribution of the film drops accounting for the peak was estimated using a screen diffusion battery. Most of the drops were found to be of submicron dimensions and concentrated in the 0.05‐ to 0.3‐ μm‐diameter size range.
Winter oceanographic conditions in the Fram Strait‐Yermak Plateau region
Authors: Muench Robin D. , McPhee Miles G. , Paulson Clayton A. , Morison James H.
Published: February 2008

Temperature, salinity and currents were measured in the Yermak Plateau and northern Fram Strait region during March–April 1989. An isothermal upper layer was near the freezing point everywhere except seaward of the ice edge near western Svalbard. Temperatures in the underlying Atlantic Water layer decreased in general toward the northwest from maximum values in the West Spitsbergen Current west of Svalbard. Mesoscale features were superimposed on this trend, and the most apparent of these was a middepth (200–300 m) warm filament overlying the northwestern flank of the plateau. Currents in the warm filament were northward, at 2–4 cm/s, for a 10‐day period in April, providing a possible advective explanation for presence of the filament. The mechanism for these currents may involve topographic control over a western extension of the north flowing West Spitsbergen Current or, alternately, rectification of diurnal currents which are enhanced by the bottom topography of the plateau. Our data favor the tidal rectification mechanism. A warm core, anticyclonic eddy associated with the filament contained Atlantic Water which was virtually unmodified from that occurring more than 200 km farther south. Characteristics of this eddy were consistent with an origin in the West Spitsbergen Current. In the upper layer, a generally cyclonic baroclinic circulation was present about the plateau. Measured upper layer current speeds were greatest (∼8 cm/s) in the southward flowing East Greenland Current, where they exceeded the baroclinic currents by approximately 1 cm/s, which may represent a southward barotropic component. Farther to the northeast, both measured and baroclinic upper layer currents were weak and variable.
A regional model study of the ozone budget in the eastern United States
Authors: McKeen S. A. , Hsie E.‐Y. , Trainer M. , Tallamraju R. , Liu S. C.
Published: February 2008

In order to better understand the photochemical and meteorological processes controlling regional scale air quality problems such as ozone formation, we have developed a three‐dimensional Eulerian model and applied this model to a high‐pressure period (July 4 to July 7, 1986) over the eastern United States. Meteorological and physical variables from a three‐dimensional primitive‐equation model are used to drive the transport parameters over a grid with 60×60 km2 horizontal resolution, and 15 unequally spaced vertical layers extending from the ground to roughly 15 km. The treatment and incorporation of the dynamic model, the transport model, surface deposition, emission of anthropogenic and natural O3 precursors, the chemical mechanism for 35 individual species, solar radiation and the numerical methods are discussed in detail. Model performance is tested by comparing model predicted O3 concentrations with observations from the U.S. Environmental Protection Agency ozone‐monitoring network. Although a significant correlation between model and observed O3 is found, systematic discrepancies also exist and are discussed in relation to the basic model formulation, and variability in the observed O3. Additionally, a comparison of time‐averaged NOx and anthropogenic nonmethane hydrocarbon (NMHC) concentrations to relatively long term observations provides a qualitative assessment of the model's ability to simulate certain aspects of these O3 precursors from the few available observations. The model is used as a diagnostic tool to analyze various aspects of regional scale O3 formation and the budgets of the primary O3 precursors. Ozone formation over much of the continental model domain is shown to be NOx. limited. On the other hand, for midday NOx levels greater than about 4 or 5 ppbv, O3 formation is generally suppressed because of the low NMHC to NOx ratios (1 to 7) that are characteristic of the emissions inventory. Regional‐scale budget analyses show that very Hide NOx or NMHC is transported to the free troposphere for the high‐pressure conditions of this study and in the absence of a significant subgrid‐scale vertical mixing process (i.e., efficient cumulus transport). We calculate a net turnover time of about 1.5 days for continental O3 below 1800 m with in situ photochemical formation being balanced by photochemical loss and transport off the American continent. The results of this work are intended to serve as a baseline for further model development.
Infrared cooling rate calculations in operational general circulation models: Comparisons with benchmark computations
Authors: Fels S. B. , Kiehl J. T. , Lacis A. A. , Schwarzkopf M. D.
Published: February 2008

As part of the Intercomparison of Radiation Codes in Climate Models (ICRCCM) project, careful comparisons of the performance of a large number of radiation codes were carried out, and the results compared with those of benchmark calculations. In this paper, we document the performance of a number of parameterized models which have been heavily used in climate and numerical prediction research at three institutions: Geophysical Fluid Dynamics Laboratory (GFDL), National Center for Atmospheric Research (NCAR), and Goddard Institute for Space Studies (GISS).
Entropy budget of the atmosphere
Authors: Peixoto José Pinto , Oort Abraham H. , De Almeida Mário , Tomé António
Published: February 2008

The balance equations for the entropy in the atmosphere are presented and discussed. Using observed energy fluxes and atmospheric temperatures, we present estimates of the various terms in the global mean entropy budget. The largest boundary fluxes of entropy are associated with the emission of longwave radiation. The fluxes of entropy associated with turbulent and molecular diffusion are found to be much smaller. On the planetary scale the mean outgoing flux of entropy at the top of the atmosphere is found to be about 22 times larger than the mean incoming flux of entropy through solar radiation. The rates of entropy production and destruction by the various irreversible processes that occur in the atmosphere are also computed. The entropy production terms involved in the release of latent heat and the absorption of solar radiation are, by far, the largest sources of entropy for the atmosphere, whereas the production of entropy associated with the absorption of longwave radiation is an order of magnitude smaller. The destruction is mainly accomplished through cooling by outgoing longwave radiation. The contributions of the sensible heat fluxes and friction are relatively small. Regional contributions to the total entropy generation in the atmosphere are studied by considering an equatorial region bounded by two latitudinal walls at 15°N and 15°S and a polar region poleward of 70°N. The rates of entropy generation by the various diabatic processes are highest in the equatorial region; part of the generated entropy is exported to higher latitudes.
Simulation of the last glacial cycle by a coupled, sectorially averaged climate—ice sheet model: 1. The climate model
Authors: Gallée H. , van Ypersele J. P. , Fichefet Th. , Tricot Ch. , Berger A.
Published: February 2008

This paper describes a sectorially averaged seasonal model developed for simulating the long‐term response of the climate system to the astronomical forcing. The model domain covers the northern hemisphere. The atmospheric dynamics is represented by an improved zonally averaged quasi‐geostrophic model. It includes a new parameterization of the meridional transport of quasi‐geostrophic potential vorticity and a parameterization of the Hadley sensible heat transport. The atmosphere interacts with the other components of the climate system (ocean, sea ice, and land surface covered or not by snow and ice) through vertical fluxes of momentum, heat and water vapor. The model explicitly incorporates detailed radiative transfer, surface energy balances, and snow and sea ice budgets. The vertical profile of the upper ocean temperature is computed by an integral mixed‐layer model which takes into account meridional convergence of heat. Sea ice is represented by a thermodynamic model including leads and a new parameterization for lateral accretion. This paper presents the model climate for present conditions and results of sensitivity experiments obtained by modifying some internal parameters or by deactivating certain parameterizations in the model. Simulation of the present climate shows that the model is able to reproduce the main characteristics of the general circulation and, in particular, the surface wind field. The seasonal cycles of oceanic mixed layer, sea ice, and snow cover are also well reproduced. Sensitivity experiments show the importance of the meridional sensible heat transport by the Hadley circulation in the tropics, the seasonal cycle of the oceanic mixed‐layer depth and sea ice formation in latitude bands where the average water temperature is above the freezing point. In a forthcoming paper, this model will be coupled to an ice sheet model and applied to the simulation of the last glacial cycle in the northern hemisphere.
Spectroscopic observations of atmospheric trace gases over Kitt Peak: 3. Long‐term trends of hydrogen chloride and hydrogen fluoride from 1978 to 1990
Authors: Wallace L. , Livingston W.
Published: February 2008

We have analyzed solar spectra obtained with the 1‐m Fourier transform spectrometer and the 13.5‐m spectrograph at the McMath telescope on Kitt Peak for absorption by hydrogen chloride and hydrogen fluoride which are largely confined to the stratosphere. During the period 1978–1990 we find that the amounts of both species have been increasing significantly; HCl at a rate of 1.0×1014 mol cm−2 yr−1 and HF at a rate of 0.37×1014 mol cm−2 yr−1. Referred to 1984 values, these rates correspond to increases of 6% yr−1 for HCl and 9% yr−1 for HF, or a factor of 2 for HCl and a factor of 3 for HF for the 12‐year period. These fractional increases are comparable to the published increases in the ground level concentrations of the halocarbons. Both gases show complicated patterns of variability superimposed on seasonal signatures. However, the tight correlation between the HCl and HF amounts is further clear evidence that a single mechanism is primarily responsible for the variability of these gases. Exceptions may be the pronounced short‐lived maxima noted in February 1982 and in February 1990 which correlate with the ash clouds from the Nyamuragira and Redoubt volcanos.
Measurements of atmospheric hydrogen peroxide in the gas phase and in cloud water at Mt. Mitchell, North Carolina
Authors: Claiborn Candis S. , Aneja Viney P.
Published: February 2008

Measurements of atmospheric hydrogen peroxide in the gas phase were made during four intensive observation periods at the Mt. Mitchell State Park, North Carolina, during the growing season (May through September) of 1988. Cloud water hydrogen peroxide was measured during the entire field season of 1988 and during the late summer and fall of 1987 (August and October). Cloud water concentrations were found to be similar to those reported from another high‐elevation location in the southeastern United States. Cloud water samples collected during these periods showed a wide range of levels (∼ 0 – 219 μM/L ) and average values of 38 μM/L and 44 μM/L for the entire sampling seasons of 1988 and 1987, respectively. Significant seasonal variation was noted both in 1987 and 1988, with cloud water levels of hydrogen peroxide much higher in the summer than in the fall. Gas‐phase hydrogen peroxide levels ranged from the detection limit (0.1 ppbv) to above 4 ppbv. Gas‐phase hydrogen peroxide demonstrated a nighttime maximum in the summer but not in the fall. The measurements taken in the fall were significantly lower than those taken during the summer, possibly due at least in part to seasonal variation. Atmospheric hydrogen peroxide levels were found to be increasing during stagnating high‐pressure systems and were found to correspond to the back trajectory of the air mass with the highest concentrations corresponding to continental air masses. The hydrogen peroxide concentration was also found to be affected by radical formation from ozone and by loss processes such as wet and dry deposition.
Effect of chemical kinetics uncertainties on calculated constituents in a tropospheric photochemical model
Authors: Thompson Anne M. , Stewart Richard W.
Published: February 2008

The imprecision of photochemical reaction rates as measured in the laboratory introduces significant uncertainty into trace species concentration calculated in a photochemical model. We have evaluated uncertainties in tropospheric concentrations calculated with a one‐dimensional photochemical model, using a Monte Carlo technique to introduce random uncertainty into the model rate coefficients. Correlations between rate coefficients and species and between species and species have been determined to answer the following questions. Which are the most critical kinetic processes in determining constituent distributions? Which are the strongest species‐species correlations? The most critical reactions turn out to be the primary photodissociations of O3 and NO2, which initiate ozone destruction and formation, respectively. The reaction between OH and methane is critical, as is the rate of nitric acid formation, which removes both odd nitrogen (NOx) and odd hydrogen (HOx). Species‐species correlations reveal anticorrelation between HOx and NOx and positive correlation between OH arid peroxides, acids, and aldehydes. Particular attention is given to ozone and to the transient OH, which is difficult to measure and is therefore frequently calculated using photochemical models and observations of more stable trace gases. A set of Monte Carlo computations is performed for conditions simulating several distinct chemical environments because imprecision in computed species are nonlinear and depend strongly on mean chemical composition. For low NOx, low hydrocarbon, low O3 levels, as in the remote troposphere, the 1 σ imprecision in computed boundary layer OH may be as low as 20%, with that for HO2 at 15% and H2O2 at 25%. At higher NOx and O3 levels, the 1σ imprecision in boundary layer OH and HO2 is 70%, and H2O2 is 90%. The 1σ imprecision in computed O3 is ∼15% (7–10 ppbv) in both cases. The implications of model computed OH imprecision for predictive and diagnostic calculations are explored. Averaging over the regionally differing results suggests that a typical estimate of global OH is ∼25% uncertain due to kinetics imprecision. This limits the certainty with which lifetimes for numerous natural and anthropogenic trace gases can be calculated with a photochemical model. The imprecision in a given determination of computed OH can be cut to 20% or less with simultaneous high‐precision measurements of O3, CO, CH4, and NO2. Several experimental strategies for optimizing the deduction of OH are described, including one based on measurement of the HO2 radical.
Three‐dimensional model synthesis of the global methane cycle
Authors: Fung I. , John J. , Lerner J. , Matthews E. , Prather M. , Steele L. P. , Fraser P. J.
Published: February 2008

The geographic and seasonal emission distributions of the major sources and sinks of atmospheric methane were compiled using methane flux measurements and energy and agricultural statistics in conjunction with global digital data bases of land surface characteristics and anthropogenic activities. Chemical destruction of methane in the atmosphere was calculated using three‐dimensional OH fields every 5 days taken from Spivakovsky et al. (1990a, b). The signatures of each of the sources and sinks in the atmosphere were simulated using a global three‐dimensional tracer transport model. Candidate methane budget scenarios were constructed according to mass balance of methane and its carbon isotopes. The verisimilitude of the scenarios was tested by their ability to reproduce the meridional gradient and seasonal variations of methane observed in the atmosphere. Constraints imposed by all the atmospheric observations are satisfied simultaneously by several budget scenarios. A preferred budget comprises annual destruction rates of 450 Tg by OH oxidation and 10 Tg by soil absorption and annual emissions of 80 Tg from fossil sources, 80 Tg from domestic animals, and 35 Tg from wetlands and tundra poleward of 50°N. Emissions from landfills, tropical swamps, rice fields, biomass burning, and termites total 295 Tg; however, the individual contributions of these terms cannot be determined uniquely because of the lack of measurements of direct fluxes and of atmospheric methane variations in regions where these sources are concentrated.
Measurements of condensation nuclei above the jet stream: Evidence for cross jet transport by waves and new particle formation at high altitudes
Authors: Wilson J. C. , Lai W. T. , Smith S. D.
Published: February 2008

Condensation nuclei (CN) were used as a tracer in mid‐latitude aircraft experiments in April and May 1984 designed to study transport in the stratosphere. A very large scale, mean distribution of CN was determined for April 20 in the plane perpendicular to the jet stream using smoothed CN measurements and very large scale, mean potential vorticity isopleths. This very large scale, mean distribution was constructed to exclude the structures associated with waves of short vertical wavelengths. A second analysis was done on filtered CN data by Danielsen et al. [this issue] to produce a CN cross section which included the effects of waves having vertical wavelengths of the order of 1 to 3 km. These two analyses and the waves inferred from the meteorological and tracer data produce a self‐consistent explanation for the observed spatial distribution of CN on April 20. The very large scale, mean CN distribution was distorted by waves which had the effect of transporting air with anticyclonic properties several degrees to the cyclonic side of the jet and created a strongly layered structure in the CN distribution.

The unfiltered CN data revealed short wavelength oscillations in the CN distribution at the interface between the transported anticyclonic air parcel and the adjacent cyclonic air mass. These oscillations were also seen in the ozone data, and they increase the potential for mixing along that interface. If the mixing does occur, then a wave mechanism for cross jet transport has been observed.

At altitudes above about 17 km, CN mixing ratios were affected by a high altitude source of new particles.
Irreversible transport in the stratosphere by internal waves of short vertical wavelength
Authors: Danielsen Edwin F. , Hipskind R. Stephen , Starr Walter L. , Vedder James F. , Gaines Steven E. , Kley Dieter , Kelly Ken K.
Published: February 2008

The U‐2 aircraft was instrumented and flown in the stratosphere during the Stratosphere‐Troposphere Exchange Project's experiments of April 1984 to provide a set of simultaneous measurements by fast responding sensors that would aid in the identification of the modes of cross‐jet transport. The measurements confirm the preexperimental deductions that transport is dominated by waves, not by large‐scale circulations. Monotonic gradients of trace constituents normal to the jet axis, with upper stratospheric tracers increasing poleward and tropospheric tracers increasing equatorward, are augmented by large‐scale confluence as the jet intensifies during cyclogenesis. These gradients are rotated, intensified, and significantly increased in area as their mixing ratio surfaces are folded by the differential transport of a very low frequency, transverse wave. The quasi‐horizontal transport produces a laminar structure with stable layers rich in upper stratospheric tracers alternating vertically with less stable layers rich in tropospheric tracers. The transport proceeds toward irreversibility as higher frequency, shear‐gravity waves extend the folding to smaller horizontal scales. It becomes irreversible when these short waves actually fold the isentropic surfaces and small‐scale mixing develops. The progression to higher wave numbers is a discrete, not a continuous, cascade with major gaps in the observed horizontal wavelengths. The wave modes are identified by matching the observed amplitudes and phases against those obtained by linear perturbation theory. Prior to mixing, the wave‐generated perturbations maintain the correlations produced by advecting the larger‐scale mean gradients; thus the high resolution measurements support the linear turbulence closure assumption.
Surface temperature fluctuations in a stochastic climate model
Authors: Kim Kwang‐Yul , North Gerald R.
Published: February 2008

This paper considers the geographical distribution of various second moment statistics from a noise‐forced energy balance climate model and compares them to the same fields derived from a 40‐year data set. The variable considered is the surface temperature field over the Earth. The energy balance model is a standardized one used in several previous studies which emphasized the geographical distribution of the seasonal cycle. It treats two‐dimensional geography explicitly by using a different (uniform) heat capacity over ocean than over land. The study compares the (spatially filtered or “smoothed”) point variance data with those generated by the model in low‐, medium‐ and high‐frequency bands. The study also examines the correlation of surface temperature fluctuations at six representative test points with those of neighboring points. The only adjustable parameter in the study is the strength of the noise forcing. The intercomparisons show that the model produces maps that look remarkably close to those from the data without too much sensitivity to the form of the driving noise.
Charging of mesospheric particles: Implications for electron density and particle coagulation
Authors: Jensen Eric J. , Thomas Gary E.
Published: February 2008

Measurements of the electron density at high latitudes in the summertime show a pronounced “bite‐out” at about 87 km. Using a numerical model of polar mesospheric cloud (PMC) formation, we have investigated the effects of ion and electron capture by ice particles on the ionization near the mesopause. The microphysical model includes all physical processes believed to be important, and the predicted PMC optical properties agree well with polarization and albedo measurements. We have calculated statistical distributions of charges on ice particles, including collection of ions and electrons by particles, and photoemission. Given these charge distributions, ionization loss rates due to capture by particles and the resulting steady‐state electron and ion densities are calculated. Our calculations indicate that aerosol concentrations associated with visible PMC are unlikely to cause a severe electron density depletion. The bite‐out could possibly be caused by a large concentration of small ice particles existing in a narrow cold layer near the mesopause. However, concentrations of ice nuclei (either dust particles or water cluster ions) on the order of 1000 cm−3 would be required. We have also found that the net negative charge on mesospheric aerosols may severely inhibit coagulation. The importance of this result is that mesospheric dust particles would not grow significantly. If this analysis is indeed correct, then mesospheric dust particles will be smaller than previously estimated, and a higher supersaturation with respect to water vapor would be required for heterogeneous nucleation of ice crystals. Hence, the existence of ice particles at the mesopause may require lower temperatures than previously assumed.
Intercomparison of total ozone data measured with Dobson and Brewer ozone spectrophotometers at Uccle (Belgium) from January 1984 to March 1991, including zenith sky observations
Authors: De Backer H. , De Muer D.
Published: February 2008

More than 7 years of quasi‐simultaneous observations of the total ozone amount measured with Dobson spectrophotometer 40 and Brewer spectrophotometer 16, both located in Uccle (50°48′N, 4°21′E), are compared. Direct Sun observations with both instruments show a significant drift relative to each other of 0.1% per year. On the other hand, the Brewer instrument measurements indicate that the SO2 amount at Uccle has had a strong downward trend of 8.9% per year over the same time period. This is confirmed by in situ measurements of SO2 density near the ground. If the SO2 trend is taken into account in the comparison between Brewer and Dobson instrument total ozone values, the two total ozone data sets show no drift with respect to each other. The question of SO2 tendency therefore deserves investigation in any trend analysis of Dobson instrument total ozone data. Quasi‐simultaneous zenith sky observations made with both instruments are also intercompared. Results indicate that the coherence between direct Sun and zenith sky data of the Brewer instrument is slightly better than that of the Dobson instrument.
Trace gas concentrations and meteorology in rural Virginia: 1. Ozone and carbon monoxide
Authors: Poulida Olga , Dickerson Russell R. , Doddridge Bruce G. , Holland Joshua Z. , Wardell R. Glenn , Watkins James G.
Published: February 2008

Carbon monoxide (CO) and ozone (O3) play a central role in the oxidizing capacity of the atmosphere. Standard meteorological parameters and concentrations of these trace gases at Big Meadows, Shenandoah National Park, Virginia, were monitored almost continuously from October 1988 to October 1989. The National Park Service has been measuring O3 at this and two other sites in the park since 1983. Seasonal, monthly, and diurnal variations of hourly averages are examined. In the winter, dry deposition dominates; ozone values are relatively low with CO and O3 negatively correlated. In the summer, photochemistry dominates; ozone values are relatively high, and CO and O3 are positively correlated. Ozone shows a yearly mean mixing ratio of 33 (σ = 12) ppbv and did not exceed the ambient air quality standard during this year. CO mixing ratios averaged 204 (σ = 51) ppbv with no discernible diurnal or seasonal variation. Histograms of hourly means of O3 and CO appear lognormal, but the chi‐square tests for goodness of fit reject the hypotheses. Several lines of evidence suggest that the data are little affected by local sources and are reasonably representative of the regional air quality. The summer of 1989 was cooler than normal, and the average ozone concentration was lower than the 7‐year mean, although an analysis of the full record illustrates no statistically significant trend.
Three‐dimensional modeling of the concentration and deposition of 210Pb aerosols
Authors: Feichter J. , Brost R. A. , Heimann M.
Published: February 2008

Two aerosol‐borne species, 210Pb and 7Be, were simulated on‐line in a low‐resolution global climate model (ECHAM2). This paper mainly considered 210Pb, which basically has its source in the lower troposphere over continents and its main sink in wet deposition. A companion paper (this issue) discussed 7Be, whose source is in the upper troposphere and whose primary sink is also in wet deposition. In order to test a simple wet scavenging parameterization in which the depletion of aerosol in a grid cell depends on the condensation rate in the grid cell, we compared simulated and observed annual average values of 210Pb concentration and deposition: the monthly average surface concentration is generally well simulated; the correlation coefficient is r = 0.79 for annual average concentration and r = 0.63 for annual average deposition, although globally the concentration averages 40% high and the deposition 18% low. Because the scavenging parameters were tuned to give good results for 7Be and reasonable agreement for 210Pb, increasing the rate of wet scavenging would usually improve the simulation of 210Pb but degrade that of 7Be. It is suggested that explicitly considering the cumulus updrafts and scavenging from the updrafts could preferentially scavenge 210Pb relative to 7Be and thus improve the 210Pb simulation without sacrificing the good 7Be agreement. On the other hand, this paper and its companion show that one can often describe the deposition and surface concentration to within about 20% for species with sources in the lower and upper troposphere with a simple “local” (in the vertical) wet scavenging parameterization. Poorer results should be expected, however, if we had tried to match simultaneously the observed concentration and deposition of a species with a true surface source and one with a true stratospheric source.
The inflatable sphere: A technique for the accurate measurement of middle atmosphere temperatures
Authors: Schmidlin F. J. , Lee H. S. , Michel W.
Published: February 2008

In recent years there has been increasing interest in the utilization of the inflatable falling sphere technique for middle atmosphere studies. The falling sphere technique uses radar position information and the equation of motion to calculate density data from which temperature information is derived. Through theoretical derivation, simulation, and measurements it is demonstrated that the temperatures derived from falling spheres are not significantly affected by linear bias in the density measurements that originate from uncertainties in sphere mass, volume, or cross‐sectional area. This study illustrates the sphere's capability to produce accurate temperatures up to 85 km and higher, given that the necessary reduction initialization conditions are met. At heights below 60 km, comparison of sphere temperatures with in situ thermistor measurements obtained close in space and time shows good agreement. Comparison with OH‐radical rotational temperatures also confirms excellent agreement at 86 km. It is concluded that the sphere technique is an independent and highly accurate source of temperature measurement, is unique in being the only low‐cost source of in situ measurement of temperature throughout the mesosphere and lower thermosphere, and qualifies as an intrinsic method to establish the accuracy of other atmospheric measurement systems.
High‐resolution, VUV (147–201 nm) photoabsorption cross sections for C2H2 at 195 and 295 K
Authors: Smith Peter L. , Yoshino Kouichi , Parkinson W. H. , Ito Kenji , Stark Glenn
Published: February 2008

Acetylene, C2H2, plays an important role in the photochemistry of the atmospheres of the giant planets, in part because of its strong absorption features in the 145–200 nm region where there is significant solar flux. Accurate photoabsorption cross section data at the temperatures of planetary atmospheres are required for interpretation of observations and for reliable photochemical models. We have measured the photoabsorption cross sections of acetylene at 195 and 295 K in the wavelength range 147–201 nm. (The 295 K measurements extend to 137 nm.) The high‐resolution spectrometers employed had instrumental bandwidths smaller than those used in previous measurements and therefore produced cross sections that are less influenced by instrumental effects. Our results indicate that hot bands make small but significant contributions to the room temperature absorption spectrum of C2H2. Photochemical models of planetary atmospheres should employ cross sections measured at the temperatures of these atmospheres.
Oceanography in the Kattegat and Skagerrak Over the Past 8000 Years
Authors: Nordberg K.
Published: February 2008

In the Kattegat, between Sweden and Denmark, a large number of cores containing Holocene seafloor deposits were investigated stratigraphically. Sedimentological, biostratigraphical, and chronostratigraphical variables were especially emphasized. Palynological and foraminiferal analyses indicate several changes in the oceanographic circulation system in the Skagerrak‐Kattegat during the Holocene. Radiocarbon datings and pollen analyses suggest that these changes occurred at 8000, 4000, 2000, between 1000 and 500, and 300 years B.P. Compilation of stratigraphical data from the region suggests that at about 8000 years B.P. the English Channel opened and the Southern Jutland Current was formed. This had a major influence on the Skagerrak, but only a marginal effect can be traced in the Kattegat. The major components of the present circulation system in the Kattegat‐Skagerrak were established about 4000 years B.P., and the subsequent changes in the circulation pattern and the inflow‐outflow system that developed at approximately 2000, 500, and 300 years B.P. are variants of these.
Timing of Late Quaternary productivity pulses in the Panama Basin and implications for atmospheric CO2
Authors: Pedersen T. F. , Nielsen B. , Pickering M.
Published: February 2008

High‐resolution percent Corg and δ18Oforam records obtained from Panama Basin core Atlantis II 54‐25PC and additional data from nearby core P7 show that enhanced burial of organic carbon has characterized every major glacial period for the last 500 kyr in that area. Both Corg concentration and mass accumulation rate profiles exhibit a sawtooth pattern with maxima occurring typically in the later stages of glacial periods. Comparison with dust records suggests that the carbon accumulation rate profile reflects both the upwelling history and a variable rate of iron input during the late Quaternary. The sawtooth character may derive from increased wind velocities and rates of upwelling during glacials which are indirectly related to ice volume (Sarnthein et al., 1988). The rapid decline in export production at the end of glacials in the equatorial Pacific may be attributed to the retreat of ice sheets (thus reduced wind velocities and upwelling) coupled with a coincident decline in atmospheric dust load and/or delivery rate. The Corg accumulation rate profiles do not correlate well with atmospheric CO2 records. For example, atmospheric CO2 was already at a minimum 40 kyr ago when production in the Panama Basin began increasing dramatically, commensurate with an increase in global dust levels. Using the relationship between the degree of photosynthetic fractionation and the concentration of free CO2 in the surface ocean postulated by Popp et al. (1989), δ13Corg measurements made on core P7 show that Panama Basin surface waters have been supplying CO2 to the atmosphere continually for at least the last 50 kyr. There is no evidence for a flux of CO2 into the surface ocean in this area at any time during this period despite the higher production. If the Panama Basin cores are representative of the eastern and central equatorial Pacific, then these observations weaken the influence on CO2 drawdown postulated for increased glacial productivity at low latitudes.
The Modellion Concept
Authors: Shuttleworth W. James
Published: February 2008

Humanity's massive intervention in natural systems is at a pace which exceeds our ability to predict its consequence on the world in which we live. As a result, we have conceived a model planet, Modellion, with much simpler terrestrial surfaces, upon which we can carry out numerical experiments to teach us, by example, about the planet Earth. Over the last decade there have been observational studies to better define this model planet and to aid its evolution toward the Earth system. This paper reviews these studies, their purpose, and the insight they have given; it then goes on to preview elements of the observational program proposed to occur under the Global Energy and Water Cycle Experiment and International Geosphere‐Biosphere Programme in the 1990s.
Trace splitting of whistlers: A signature of fine structure or mode splitting in magnetospheric ducts?
Authors: Hamar D. , Ferencz Cs. , Lichtenberger J. , Tarcsai Gy. , Smith A. J. , Yearby K. H.
Published: February 2008

Previously, we reported on the discovery of fine structure in whistler data received on the ground at Halley, Antarctica. This structure was not apparent in conventional spectral analysis but was revealed by the technique of digital matched filtering. We have now examined a larger data set, and a commonly observed phenomenon is that single whistler traces become split into two, over various frequency ranges. Examples are presented in the form of time‐transformed spectrograms in which reference model whistlers are represented as vertical lines. The splitting is typically 5–15 ms (about 0.5% of the total whistler travel time) and extends over frequency ranges of a few hundred hertz which may occur anywhere between the upper and lower cutoff frequencies of the whistler. The splitting may be either symmetrical or unsymmetrical with respect to the unsplit trace. The effect is unlikely to arise in the spectrum of the lightning source or from propagation under or through the ionosphere. It may, however, be a signature of field‐aligned fine spatial structure in plasmaspheric density, and hence refractive index, in the whistler duct. For simple longitudinal propagation, electron density fluctuations of the order of 1% and spatial scale sizes of the order of 50 km in the equatorial plane are implied. It seems possible that the observations could also be interpreted in terms of the mode theory of ducted propagation, assuming the excitation of two modes with group velocities differing by a few tenths of a percent.
Turbulence scattering layers in the middle‐mesosphere observed by the EISCAT 224‐MHz radar
Authors: Collis P. N. , Rietveld M. T. , Röttger J. , Hocking W. K.
Published: February 2008

Spectral measurements of signals scattered from altitudes well below 70 km have for the first time been obtained with the EISCAT 224‐MHz radar. Observations with the antenna pointing away from the vertical at times show spectral power distributions departing markedly from those expected from collision‐dominated incoherent scatter theory. Separated peaks in the spectra occur in regions of abrupt shear in the velocity of the neutral wind within the scattering volume. Anomalously large backscattered power levels are sometimes observed in the vicinity of such shears at altitudes near 68 km. It is unlikely that these echoes are due to incoherent (Thomson) scatter. Instead, it is proposed that the abrupt velocity shears develop neutral turbulence in narrow layers and that these layers cause the enhanced backscatter. Calculations of the expected backscatter power levels at 224 MHz for incoherent scatter and for turbulence scatter show that the turbulence component can be the dominant one at heights below about 68 km if the potential refractive index gradient and the turbulence energy dissipation rates are large enough.
Spaced‐antenna analysis in the frequency domain
Authors: Briggs B. H. , Vincent R. A.
Published: February 2008

Data from spaced‐antenna experiments are normally analysed by correlation techniques in the time domain, but several authors have recently pointed out that an equivalent analysis can be carried out in the frequency domain. To explore any possible advantages of such a procedure, we assume Gaussian forms for the correlation functions so that their Fourier transforms can be evaluated analytically. The power spectrum is shown to be a convolution of two terms, one of which represents “beam broadening” due to the mean wind, and the other represents the broadening due to turbulent motions. The cross spectrum has a phase which is a linear function of frequency, the slope of which is related to the “apparent velocity” of correlation analysis. If this same cross‐spectral phase is interpreted by the method of Doppler interferometry, the velocity obtained is also the apparent velocity. The Gaussian model is extended to include the effects of vertical velocity and of scatter which is centered off zenith. A computational scheme is presented in which an analysis equivalent to conventional “full correlation analysis” is carried out entirely in the frequency domain. The method is illustrated using data from Adelaide.
Seismicity and fault interaction, Southern San Jacinto Fault Zone and adjacent faults, southern California: Implications for seismic hazard
Authors: Petersen Mark D. , Seeber Leonardo , Sykes Lynn R. , Nábělek John L. , Armbruster John G. , Pacheco Javier , Hudnut Kenneth W.
Published: February 2008

The southern San Jacinto fault zone is characterized by high seismicity and a complex fault pattern that offers an excellent setting for investigating interactions between distinct faults. This fault zone is roughly outlined by two subparallel master fault strands, the Coyote Creek and Clark‐San Felipe Hills faults, that are located 2 to 10 km apart and are intersected by a series of secondary cross faults. Seismicity is intense on both master faults and secondary cross faults in the southern San Jacinto fault zone. The seismicity on the two master strands occurs primarily below 10 km; the upper 10 km of the master faults are now mostly quiescent and appear to rupture mainly or solely in large earthquakes. Our results also indicate that a considerable portion of recent background activity near the April 9, 1968, Borrego Mountain rupture zone (ML=6.4) is located on secondary faults outside the fault zone. We name and describe the Palm Wash fault, a very active secondary structure located about 25 km northeast of Borrego Mountain that is oriented subparallel to the San Jacinto fault system, dips approximately 70° to the northeast, and accommodates right‐lateral shear motion. The Vallecito Mountain cluster is another secondary feature delineated by the recent seismicity and is characterized by swarming activity prior to nearby large events on the master strand. The 1968 Borrego Mountain and the April 28, 1969, Coyote Mountain (ML=5.8) events are examples of earthquakes with aftershocks and subevents on these secondary and master faults. Mechanisms from those earthquakes and recent seismic data for the period 1981 to 1986 are not simply restricted to strike‐slip motion; dipslip motion is also indicated. Teleseismic body waves (long‐period P and SH) of the 1968 and 1969 earthquakes were inverted simultaneously for source mechanism, seismic moment, rupture history, and centroid depth. The complicated waveforms of the 1968 event (Mo=1.2 × 1019 N m) are interpreted in terms of two subevents; the first caused by right‐lateral strike‐slip motion in the mainshock along the Coyote Creek fault and the second by a rupture located about 25 km away from the master fault. Our waveform inversion of the 1969 event indicates that strike‐slip motion predominated, releasing a seismic moment of 2.5 × 1017 N m. Nevertheless, the right‐lateral nodal plane of the focal mechanism is significantly misoriented (20°) with respect to the master fault, and hence the event is not likely to be associated with a rupture on that fault. From this and other examples in southern California, we conclude that cross faults may contribute significantly to seismic hazard and that interaction between faults has important implications for earthquake prediction.
A left‐lateral strike‐slip fault seaward of the Oregon Convergent Margin
Authors: Appelgate Bruce , Goldfinger Chris , MacKay Mary E. , Kulm LaVerne D. , Fox Christopher G. , Embley Robert W. , Meis Philip J.
Published: February 2008

We have mapped a recently active left‐lateral strike‐slip fault (the Wecoma fault) on the floor of Cascadia Basin west of the Oregon convergent margin, using SeaMARC I sidescan sonar, Seabeam bathymetry and multichannel seismic and magnetic data. The fault intersects the base of the continental slope at 45°10′N and extends northwest (293°) for at least 18.5 km. The fault's western terminus was not identified, and the eastern end of the fault splays apart and disrupts the lower continental slope. The fault extends to the base of the 3.5‐km‐thick sedimentary section and overlies a basement discontinuity that may be related to movement along the Wecoma fault. Prominent seafloor features crosscut by the fault individually display between 120 and 2500 m of left‐lateral separation, allowing the general history of fault motion to be evaluated. The fault's average slip rate since 10–24 ka is inferred to be 5–12 mm/yr, based on the age of an offset submarine channel. Surficial structural relationships, in conjunction with the maximum inferred slip rate, indicate that fault movement initiated at least 210 ka and that the fault has been active during the Holocene.
Tectonic evolution of the Japanese islands as reflected in modal compositions of Cenozoic forearc and backarc sand and sandstone
Authors: Marsaglia Kathleen M. , Ingersoll Raymond V. , Packer Bonnie M.
Published: February 2008

Cenozoic tectonic evolution of the Japanese rifted continental arc‐trench system is reflected in the detrital modes of sand and sandstone deposited in forearc and backarc basins sampled by the Deep Sea Drilling Project. At present, the Japan arc is divided into two segments along a complex plate boundary where the Izu‐Bonin Ridge intersects the Japan arc, creating two triple junctions, in front of and behind the ridge. Southwest of the Izu‐Bonin Ridge, quartzofeldspathic Cretaceous forearc sediments were uplifted and recycled into Tertiary forearc deposits in response to strike‐slip movement associated with backarc spreading in the Shikoku basin. Quaternary forearc sections record the first major influx of volcanic detritus to southwest Japan sites. Triple‐junction‐related deformation in central Honshu has produced sand of mixed volcanic/sedimentary provenance, which is funneled by the Suruga Canyon into the Nankai Trough along the southwest Japan margin. North of the triple junction, Oligo‐Miocene forearc sand compositions indicate Oligocene forearc uplift and volcanism, possibly related to initial backarc rifting and formation of the Japan Sea, and subsequent Miocene exposure of arc basement. In contrast, Pliocene and Quaternary forearc sand from northeast Japan is primarily volcaniclastic and documents uninterrupted arc volcanism. Within the backarc region, sand compositions vary from east to west across the Japan Sea. The Asian rifted continental margin and submerged remnants shed quartzofeldspathic sand into the western side of the basin, whereas the Japan arc sheds volcaniclastic sand into the eastern side of the basin.