bluuebunny/crossref_metadata_2025 huggingface dataset:
Metal silicate mixtures: Spectral properties and applications to asteroid taxonomy
Authors: Cloutis Edward A. , Gaffey Michael J. , Smith Dorian G. W. , Lambert Richard St J.
Published: February 2008

The reflectance spectra of combinations of olivine, orthopyroxene, and iron meteorite metal show systematic variations in spectral properties which can be used to constrain many of the physical and chemical properties of the assemblages. The presence of metal most noticeably affects band area ratios, peak:peak and peak:minimum reflectance ratios, and band widths. These parameters are also affected to varying degrees by the abundance and grain size of the metal and silicates and the composition of the silicates. Band width and band areas are useful for determining metal abundance in olivine+metal and orthopyroxene+metal assemblages, respectively. Mafic silicate grain size variations are best determined using band depth criteria. Band centers are most useful for determining mafic silicate composition. Analysis of the reflectance spectrum of the S‐class asteroid (8) Flora on the basis of these spectral parameters indicates a surface composed of approximately 50 wt % metal, 40 wt % olivine (Fa = 35±10), 10 wt % orthopyroxene (Fs = 30−25+35), and perhaps a few weight percent of clinopyroxene. A substantial amount of the surface seems to consist of a fine‐grained (<45 μm size) component. Analysis of the reflectance spectrum of the A‐class asteroid (446) Aeternitas suggests a surface assemblage of approximately 35 wt % metal, 55 wt % olivine (Fa = 20±10), 7 wt % clinopyroxene (Fs <17%), and 3 wt % orthopyroxene (Fs <45). A substantial fine‐grained (<45 μm size) surface component is also indicated for this asteroid.
Spectral albedo and emissivity of CO2 in Martian polar caps: Model results
Authors: Warren Stephen G. , Wiscombe Warren J. , Firestone John F.
Published: February 2008

A model originally developed to explain the spectral albedo and emissivity of terrestrial snow is extended to the case of carbon dioxide snow on Mars. The variation of albedo and emissivity with wavelength is caused by the spectral variation of the absorption coefficient of solid CO2. The most important variables controlling the radiative properties are grain size and contamination by dust or water. Solar zenith angle and snowpack thickness are of less importance. The observation that red albedo is higher than blue albedo in the Martian south polar cap indicates that the snow is contaminated with red dust. The interband absorption coefficient of CO2 ice in the thermal infrared is 2–3 orders of magnitude smaller than that of H2O ice, due to the absence of hydrogen bonding in CO2. This allows CO2 snow emissivity to be sensitive to grain size, emission angle, and impurities, in contrast to water snow which is nearly a blackbody under all conditions. The emissivity of CO2 snow varies substantially with wavelength, so energy budget modeling should be done in spectral detail. The addition of a thin layer of water frost over CO2 snow dramatically raises the thermal emissivity but causes little change to the spectrally averaged albedo unless the underlying CO2 snow is dirty. Remote sensing of CO2 grain size, H2O content, and dust content may be possible. However, the design of a remote‐sensing strategy awaits more accurate laboratory determination of the optical constants of CO2 ice.
Regional aeolian dynamics and sand mixing in the Gran Desierto: Evidence from Landsat thematic mapper images
Authors: Blount Grady , Smith Milton O. , Adams John B. , Greeley Ronald , Christensen Phillip R.
Published: February 2008

Spatial variations in sand composition were mapped on a regional scale in a terrestrial sand sea, the Gran Desierto of Sonora, Mexico. Mesoscale mapping on a satellite image base allowed quantitative interpretation of the dynamic development of sand sheets and dunes. The results were used to interpret the Quaternary geologic history of the tectonically active region at the mouth of the Colorado River. Landsat thematic mapper multispectral images were used to predict the abundance of different mineralogies of sand grains in a mixed aeolian terrain. A spectral mixing model separated the effects of vegetation and topographically induced shading and shadow from the effects produced by different mineral and rock types. Compositions determined remotely agreed well with samples from selected areas within the spectral limitations of the thematic mapper. A simple discrimination capability for active versus inactive sand surfaces is demonstrated based upon differences in the percentage of low‐albedo accessory grains occurring on dormant aeolian surfaces. A technique for discriminating between low‐albedo materials and macroscopic shade is implemented by combining thermal images with the results of the spectral mixing model. The image analysis revealed important compositional variations over large areas that were not readily apparent in the field.
Melting of enstatite (MgSiO3) from 10 to 16.5 GPa and the forsterite (Mg2SiO4)‐majorite (MgSiO3) eutectic at 16.5 GPa: Implications for the origin of the mantle
Authors: Presnall D. C. , Gasparik T.
Published: February 2008

A split sphere multianvil apparatus (USSA 2000) has been used to determine the melting curve of enstatite (MgSiO3) from 10 to 16.5 GPa and the forsterite (Mg2SiO4)‐majorite (MgSiO3) eutectic at 16.5 GPa. Use of a new capsule material, rhenium, allowed long runs of up to 2 hours at temperatures up to 2380°C with no observed contamination of the sample and with stable temperature control. Melting temperatures of enstatite are up to 160°C higher than those of Kato and Kumazawa (1986a). Two invariant points have been located, one for orthoenstatite+clinoenstatite+liquid at 2230°C, 11.9 GPa, and one for clinoenstatite+majorite+liquid at 2370°C, 16.4 GPa. Forsterite melts incongruently at 2350°C, 16.5 GPa to liquid and AnhB (Mg14Si5O24). In the system Mg2SiO4‐MgSiO3 at 16.5 GPa, the forsterite‐majorite eutectic has been located at 34 wt % Mg2SiO4, a composition similar to that determined by Kato and Kumazawa (1986a) at 20 GPa but much lower in Mg2SiO4 than several previous estimates based on melting experiments on mantle peridotite compositions. This forsterite‐poor location for the eutectic is in apparent conflict with the suggestion that the peridotitic upper mantle is a crystallized eutectic‐like liquid formed at about 16 GPa.
An in situ X ray diffraction study of the kinetics of the Ni2SiO4 olivine‐spinel transformation
Authors: Rubie D. C. , Tsuchida Y. , Yagi T. , Utsumi W. , Kikegawa T. , Shimomura O. , Brearley A. J.
Published: February 2008

Using the “MAX‐80” cubic‐anvil high‐pressure apparatus with synchrotron radiation, X ray diffraction experiments have been carried out to study the kinetics of the Ni2SiO4 olivine‐spinel transformation at 3.6–4.8 GPa and 740°–980°C. The Ni2SiO4 olivine‐spinel equilibrium boundary has also been redetermined. The starting material for the kinetic experiments was Ni2SiO4 olivine which was hot‐pressed in situ at 980°C and 2.5 GPa for 1.5 hours. During the transformation, X ray diffraction patterns were collected at intervals of either 30 s or 120 s, and estimates of the volume fraction transformed as a function of time have been made from the relative intensities of a total of six diffraction peaks by a least squares procedure. Although the Avrami rate equation can be fitted to the data, it is shown that this equation cannot be used as a basis for extrapolating the results to other temperatures and pressures. Instead, by fitting a more fundamental rate equation for grain boundary nucleation and interface‐controlled growth to the transformation‐time data, rates of nucleation and growth have been estimated. The activation energy for growth at 3.6–3.7 GPa has been estimated as 438 (±199) kJ mol−1. A rate equation has also been fitted to explain the dependence of the estimated nucleation rates on temperature and pressure. The results suggest that because of the kinetics of nucleation, the olivine‐spinel equilibrium boundary needs to be overstepped by ∼0.4 GPa at relatively high temperature (e.g., 1000°C) for the transformation to start, even on a geological time scale. Although the kinetics cannot be evaluated quantitatively at the low temperatures (500°–600°C) which are predicted to occur within subducting slabs at a depth of 300–400 km, the results are consistent with olivine surviving metastably to very significant depths below the equilibrium phase boundary. The results emphasize the importance of understanding the dependence of the rates of nucleation and growth on pressure and temperature when extrapolating experimental kinetic data for this type of transformation to geological conditions.
Volcanic history and tectonic development of the Central High Cascade Range, Oregon
Authors: Taylor Edward M.
Published: February 2008

Two distinct volcanic assemblages characterize the central Cascades of Oregon. The earlier, larger, and longer lived of the two is part of a calc‐alkaline, continental margin andesite belt exposed in the Western Cascades. The younger assemblage, conventionally known as the “High Cascades,” overlies the eastern part of the older assemblage and extends eastward to the Deschutes Valley. The High Cascades are also calc‐alkaline, but mafic components of a broad lava flow platform surround isolated silicic centers. A short‐lived episode of subsidence produced a graben within the central High Cascades, Subsequent mafic eruptions largely filled the graben, while the silicic centers continued to be active. This twofold volcanic development followed by extreme localized crustal extension is ascribed to the influence of slow circulating currents in the sub‐Cascade mantle, induced by drag against the subducted slab. Circulation of the lithosphere was enhanced by prolonged metasomatism and loss of strength in the mantle wedge; similar circulation may be a common or even essential component of volcanism above other subduction systems. The rates of convergence and subduction have decreased in the Cascade system to a degree that has permitted conductive heating of the slab and adjacent mantle. Circulation has migrated to higher levels within the mantle wedge, causing a more direct interaction with the crust, development of a new mafic‐dominated volcanic assemblage, and graben subsidence.
Localization of intermediate‐term earthquake prediction
Authors: Kossobokov V. G. , Keilis‐Borok V. I. , Smith S. W.
Published: February 2008

Relative seismic quiescence within a region which has already been diagnosed as having entered a “Time of Increased Probability” (TIP) for the occurrence of a strong earthquake can be used to refine the locality in which the earthquake may be expected to occur. A simple algorithm with parameters fitted from the data in Northern California preceding the 1980 magnitude 7.0 earthquake offshore from Eureka depicts relative quiescence within the region of a TTP. The procedure was tested, without readaptation of parameters, on 17 other strong earthquake occurrences in North America, Japan, and Eurasia, most of which were in regions for which a TIP had been previously diagnosed. The localization algorithm successfully outlined a region within which the subsequent earthquake occurred for 16 of these 17 strong earthquakes. The area of prediction in each case was reduced significantly, ranging between 7% and 25% of the total area covered by the TIP.
A petrologic comparison of Triassic plutonism in the San Gabriel and Mule Mountains, southern California
Authors: Barth Andrew P. , Tosdal R. M. , Wooden J. L.
Published: February 2008

Triassic magmatism in the southwest U.S. Cordillera forms a semicontinuous magmatic arc extending from northwestern Nevada to southeastern California. Quartz monzodioritic and quartz monzonitic rocks and associated diorites and granites are widespread in southeastern California, and we suggest that these rocks represent exposure of a structurally deeper part of the Triassic arc, where it was emplaced into comparatively thick Proterozoic crust. Elemental and isotopic data suggest that Triassic quartz monzodiorites and quartz monzonites in the Mule and San Gabriel Mountains were derived from a relatively undepleted, nonradiogenic mafic lithospheric source, with virtually no upper crustal interaction. Very limited data for associated Triassic(?) diorites indicate a wide range in composition and a surprisingly radiogenic isotopic signature. Younger Triassic(?) granites record a strong geochemical signature of interaction with continental crust, including inherited zircon and high initial Sr ratios but comparatively less radiogenic Pb isotopic compositions. The major and trace element geochemistry of Late Triassic plutonic rocks in southeastern California is similar in many respects to alkalic components of the Triassic arc in the Mojave Desert. However, contemporaneous rocks farther north have a calc‐alkalic signature, perhaps reflecting the variation in age and composition of lithosphere across which the Triassic arc was constructed.
Chronologic and isotopic framework for Early Proterozoic crustal evolution in the eastern Mojave Desert Region, SE California
Authors: Wooden J. L. , Miller D. M.
Published: February 2008

The Early Proterozoic geologic evolution of the eastern Mojave Desert region, as defined by characteristics of its supracrustal rocks, granitoids, metamorphism, structural history, and Pb and Nd isotopic signature, contrasts sharply with other Proterozoic provinces of the southwestern United States. The oldest supracrustal rocks of the Mojave Desert region contain zircons over 2.0 Ga, corroborating Nd isotopic evidence for a much older crust here than elsewhere in the southwestern United States. Granitoids widely emplaced within these supracrustal rocks range from 1.76 to 1.64 Ga. The earlier plutons and surrounding supracrustal rocks were metamorphosed to granulite and high amphibolite facies throughout the province at about 1705 Ma in a migmatite‐producing event that we term (informally) the Ivanpah orogeny. Subsequent granitoids, emplaced from 1.69 to 1.67 Ga, were voluminous along a north trending belt in the middle of the Mojave province. Younger plutons were emplaced at about 1.66 Ga in several places and at about 1.64 Ga along the extreme southern part of the province. Commonalities between the Proterozoic evolutions of the Mojave and Arizona crustal provinces do not conclusively establish the time that the provinces were juxtaposed; the data only suggest that the juxtaposition occurred between about 1.76 and 1.64 Ga.
The effect of internal waves on surface wind waves 2. Theoretical analysis
Authors: Hughes B. A.
Published: February 2008

A theoretical description is given of the behavior of a broadband, small‐amplitude wind wave field in a perturbing internal wave velocity pattern. The theory includes the effect of the local wind. Specific predictions are made for the case of weak internal wave currents, and these predictions are compared with measurements. The theory predicts the magnitude of the mean square slope changes reasonably well, and it predicts the quadrant of the phases correctly. General features of the perturbed surface wave energy spectrum integrated in angle are also predicted reasonably well, and comparisons are made of the theoretical and measured local integrated spectrum at roughened areas and at slick areas.
A simple theoretical model for the flow of an estuary onto a continental shelf
Authors: Beardsley Robert C. , Hart John
Published: February 2008

A simple theoretical model is developed to describe the steady flow of an estuary onto an adjacent continental shelf. A two‐layer density stratification is assumed for the shelf water, and the fluid motion is driven by the positive (upper layer) and negative (lower layer) mass fluxes associated with a pair of point sources located at the mouth of the estuary. The dynamics are linear and include the effects of Coriolis acceleration, turbulent friction, and bottom topography. Analytic solutions for the one‐layer single‐source problem are found for two special depth profiles. A boundary layer solution is found for the power law depth profile h(y) = αyk, and a global solution is found for the log law profile h(y) = H0 [1 + α 1n (y/ Lb)] for small α ≪ 1. Both solutions indicate that the far‐field flow is asymmetrically concentrated toward the right‐hand coast in the northern hemisphere, a consequence of the basic balance between topographic vortex stretching and bottom friction. This mechanism also applies when a constant along‐shore current is present. In the two‐layer case the flow in the upper layer generally tends to be concentrated toward the left‐hand coast, since the upper fluid feels (1) the interface and not the bottom topography and (2) the interfacial drag exerted by the lower fluid toward the right‐hand coast. A brief comparison is made between model predictions and observations for the Hudson and Chesapeake Bay estuaries.
An abyssal shear zone
Authors: Broecker Wallace S. , Bainbridge Arnold
Published: February 2008

At Geochemical Ocean Sections Study station 28, in the basin east of the Newfoundland Ridge, dramatic evidence for the ‘underthrusting’ of the benthic boundary layer was encountered. Results from the continuous temperature, salinity, and nephel measurements and from discrete water samples are presented in order to document that strong shearing within the near‐bottom water column must occur in this area. These observations amplify previous observations that Denmark Strait overflow water penetrates as a thin wedge far to the south of its place of origin.
Internal Kelvin waves in a Fjord Lake
Authors: Hamblin P. F.
Published: February 2008

It is argued theoretically that internal oscillations in a fjord lake have a three‐dimensional nature during the stratified period. A dynamical model is proposed that is based on the approximation that for Kelvin waves the component of flow parallel to the isobaths is much larger than the normal component. A general method of solution of the model equations is outlined which takes into account the details of the shoreline configuration, bathymetry, and density structure and is applied to the long‐period oscillations of the thermal structure of Kamloops Lake. Six episodes of internal seiches of the first vertical and longitudinal mode were examined during the period from May to November. Numerical computations predict that periods range from 33 to 140 hours and that the largest isotherm displacements occur in the region of slower phase speed in the western portion of the lake. These findings are confirmed both by visual inspection and spectral analysis of the isotherm displacements at three locations in the lake and by wind records. The unusual characteristics of the thermal structure in the lake are shown to exert a stabilizing influence on large‐amplitude wave disturbances. Long‐period internal waves are generated primarily by suddenly imposed and vigorous wind forcing along the axis of the lake.
The dependence of lightning return stroke characteristics on latitude
Authors: Thomson E. M.
Published: February 2008

The hypothesis that interstroke intervals and the mean number of strokes per lightning flash to ground vary systematically with latitude is tested using statistical methods. The weighted regression lines relating 〈log t〉 and 〈n〉 to the latitude, λ in degrees), are 〈log t〉 = 1.75 + 5.3 × 10−4λ and 〈n〉 = 4.4 ‐ 2.5 ×10−2λ, where t is the interstroke interval and n the number of strokes per flash. However, in each case, correlation is not significant at the 5% level of confidence, so that the data generally do not show a systematic latitude dependence. Latitude does appear to affect the distributions of log t in that the tropical distributions of log t are fairly consistent (within the 5% confidence limits using analysis of variance),whereas fluctuations in the nontropical distributions of log t cannot be explained in terms of random variations, but this may be an effect of differing measurement techniques. Year‐to‐year fluctuations in the observed distributions of the number of strokes per flash are shown to be statistically significant for both a tropical and a nontropical locality and may account for the considerable differences between distributions of n at different localities.
The generation of equatorial currents
Authors: Philander S. G. H. , Pacanowski R. C.
Published: February 2008

In response to the sudden onset of zonal winds the surface layers of the ocean accelerate in the direction of the wind. Motion is most intense near the equator where a jet forms within a week. The next stage in the evolution of equilibrium conditions is associated with wave fronts, excited initially at the coasts, that propagate across the ocean basin and establish zonal density gradients. Wave modes trapped in and above the strong shallow tropical thermocline because of internal reflection there are responsible for the adjustment of the upper ocean in low latitudes. These thermocline‐trapped modes extend over a depth greater than that of the wind‐driven surface currents and hence give rise to an undercurrent in the thermocline. This undercurrent is zonal and particularly intense near the equator, where it appears in the wake of an eastward traveling Kelvin or westward traveling Rossby wave after about 1 month. In the case of eastward winds, nonlinearities intensify the eastward equatorial surface jet and weaken the westward undercurrent. In the case of westward winds a different nonlinear mechanisms intensifies the eastward Equatorial Undercurrent and weakens the westward surface flow. In a 5000‐km wide basin, equilibrium equatorial currents are established about 150 days after the onset of the winds. The response time of the ocean below a depth of a few hundred meters is much longer. Winds with no spatial and a simple temporal structure generate currents with a complex vertical structure in the deep ocean. Closed current systems are possible in a confined forced region of an unbounded ocean; meridional coasts are not essential for their maintenance. The intensity of equatorial current is sensitive to dissipation parameters.
M2 tidal effects in greater Cook Strait, New Zealand
Authors: Bowman Malcolm J. , Kibblewhite Alick C. , Ash David E.
Published: February 2008

The application of an M2 nonlinear numerical tidal model to the shelf seas of central New Zealand (∼38,500 km2 area) is described. It has provided a preliminary assessment of tidal and residual currents, bottom stress, energy dissipation, and the stratification index. The existence of a permanent, tidally driven mesoscale eddy (∼75 km diameter) is predicted north of D'Urville Island. Large spatial gradients in bottom stress qualitatively agree with many features of the surficial sediment distribution. A comparison of all available bulk stratification data with the h/u3 stratification index clearly demonstrates the dominance of tidal versus wind mixing over the control of summer stratification. A potential application of the model to fisheries science is suggested through a comparison of the stratification index contour map and some observations of squid fishing vessel locations.
On the force‐restore method for prediction of ground surface temperature
Authors: Lin J. D.
Published: February 2008

The force‐restore method for prediction of ground surface temperature is investigated in view of the large temperature gradient that generally exists on a bare ground surface after an extended period of evaporation. The rate equation for the ‘ground surface’ temperature is rederived. The result from a numerical experiment indicates that there can be significant differences in the diurnal variation of ground surface temperature depending upon its definition. The method was tested by a simulation study of two field‐measured data sets at different experiment sites.
Some effects of the emissions of explosive volcanoes on the stratosphere
Authors: Cadle Richard D.
Published: February 2008

A previously published 2‐D numerical model of the global dispersion of an eruption cloud in the stratosphere as a function of time assumed an instantaneous injection of the eruption cloud (the source function). New calculations show that the dispersion rate is quite insensitive to the manner of introducing the source function into the model, including spreading the eruption time over 10 days. Results obtained by flying through the eruption clouds from explosive volcanoes in Guatemala indicated that most of the sulfur in such clouds is SO2. If, as is generally believed, SO2 reacts with OH in the stratosphere, leading to the production of H2SO4 droplets, hugh explosive eruptions can deplete the stratosphere of OH for long time periods. The OH is thus controlled by the rate of O(1D) formation from ozone. By using the results from the 2‐D dispersion model referred to above applied to the eruption cloud from the 1963 Agung eruption, and chemical kinetic rate constants, the ‘e folding’ residence time for sulfur dioxide conversion to sulfuric acid was estimated to be about 300 days. The Guatemala studies showed that the eruption clouds from explosive volcanoes contain large amounts of HCl. Unless much of this HCl is removed by rain accompanying the eruption, this HCl might be expected to have a marked influence on stratospheric chemistry as a result of the reaction OH + HCl → H2O + Cl. The volcanic HCl will probably remove OH much less rapidly than will SO2, and if the OH concentration is greatly decreased by the SO2, the above reaction may be too slow to be important.
Stratospheric hydroxyl radical concentrations: New limitations suggested by observations of gaseous and particulate sulfur
Authors: Turco R. P. , Whitten R. C. , Toon O. B. , Inn E. C. Y. , Hamill P.
Published: February 2008

A one‐dimensional aerosol model is used to investigate the sensitivity of the stratospheric distributions of gaseous sulfur compounds and sulfate aerosol particles to changes in OH and CS2 concentrations, in eddy diffusion coefficients, and in key chemical rate constants. By comparing model predictions with recent observational data for SO2, OCS, and participates, the following conclusions are reached. With regard to atmospheric sulfur, it appears that CS2 is only a secondary source of sulfur for the stratosphere relative to OCS and that background tropospheric CS2 concentrations are likely to be <70 pptv. It is also found that under stratospheric conditions, the rate coefficients for the reactions of OH with OCS and CS2 may be substantially smaller than the room temperature laboratory values of Kurylo (1978). The most important conclusion of the present study, however, is that OH concentrations below 30 km may be overestimated by a factor of 3 or more in current photochemical models. A variety of observational evidence is discussed which supports this conclusion, including measurements of HNO3/NO2 concentration ratios and ClO mixing fractions. Plausibility arguments for lower atmospheric OH concentrations are supported by recent laboratory studies of the pressure, the temperature, and the humidity dependences of OH and HO2 chemical kinetic systems. New reaction rate data bearing on this problem are reviewed. A reduced level of stratospheric OH has strong implications for ozone perturbations attributable to aircraft NOx emissions, to nitrogen fertilizer usage, and to halocarbon releases. Such ozone perturbations are simulated using a one‐dimensional atmospheric photochemistry model in which the OH concentrations are reduced in accordance with the sulfur sensitivity tests highlighted above. Owing to the reduction in OH, SST NOx injections at 20 km act to decrease ozone, not increase it as had been thought previously. Nitrous oxide produced by fertilizer decomposition is also found to be more destructive of ozone. On the other hand, fluorocarbon‐induced ozone depletions are somewhat smaller.
An evaluation of a Sun‐weather mechanism using a general circulation model of the atmosphere
Authors: Hunt B. G.
Published: February 2008

A hemispheric general circulation model has been used to investigate the impact of a high latitude ozone deficit in the stratosphere induced by a solar proton event. A hypothesis is presented which delineates the various aspects of how such an event could affect tropospheric synoptic conditions. Two experiments, with a transient ozone deficit equal to 6% of the total ozone column, were performed corresponding to different synoptic conditions, together with appropriate control and noise experiments. A trigger mechanism was presumably activated in the model because a strong enhancement, 25%, in the strength of the mean zonal wind speed in the mid‐latitude upper troposphere was obtained together with other responses, 20–24 days after the ozone deficit was inserted. This large response was identified with the ozone deficit being located in the region of the wave guide controlling the wave energy flux between the tropospheric mid‐latitudes and the high latitude stratosphere. This wave guide apparently focused the effects of the ozone deficit and provided the requisite mechanical linkage to the troposphere. An additional experiment with the ozone deficit located at 45° latitude failed to produce a similar response. Detailed analysis of hemispheric, zonal, and local meteorological changes is presented. The results are broadly supportive of a possible sun‐weather effect.
Modeling the geostrophic drag coefficient for AIDJEX
Authors: Brown R. A.
Published: February 2008

A model of the planetary boundary layer flow over the Arctic pack ice was found to relate geostrophic flow determined from a large‐scale pressure field to the surface stress vector. A summary of the model and some data comparison is presented.
Tidal effects on long‐range sound transmission
Authors: Munk W. , Zetler B. , Clark J. , Glll S. , Porter D. , Spiesberger J. , Spindel R.
Published: February 2008

Time series of acoustic travel times over long distances have significant tidal components. We discuss three experiments: First, for a 900 km westward transmission from a moored source southwest of Bermuda, the M2 constituent (apart from mooring motion) of 8 ms can be accounted for by a variable propagation with and against the 2 cm/s barotropic tidal current. The situation is different for the K1 and S2 constituents (which have a significant solar component), particularly for rays with shallow turning points, suggesting an effect from a minute daily variation in the temperature of the upper 100 m. Second, for a 500 km transmission from the Bahamas northward and parallel to the continental margin, the measured M2 constituent is not in phase with the computed effect of the barotropic tidal current, unlike the westward transmission mentioned above. Here the mode conversion from barotropic to baroclinic tides plays a crucial role: the principal cause of the travel time oscillations in quadrature with the tidal current is a vertical oscillation by several meters (and attendant temperature and sound speed fluctuations) associated with the baroclinic tide just seaward of the continental margin, in the near‐zone of mode conversion. Third, for 300 km transmissions from a moored source northwest of Bermuda to both a moored receiver and a landbased receiver, the tidal components in the travel time are dominated by tidally induced mooring motions. The tidal amplitude varies in time as the tidal mooring motion is modulated by the variable current (because of the nonlinear drag), and the current can be so estimated. An important part, possibly a predominant part, of the (nontidal) travel time variation of 0.7 s is evidently associated with the mean mooring motion.—The interpretation of the tidal fluctuations in travel time is varied and complex.
Pressure broadening of ClO by nitrogen
Authors: Pickett H. M. , Brinza D. E. , Cohen E. A.
Published: February 2008

The temperature and pressure dependence of line widths for the
and
transitions of ClO have been determined by microwave spectroscopy. The widths for both transitions are found to be the same within experimental error. The width parameter for nitrogen broadening is 3.35±0.17 MHz/torr at 317 K and 4.44±0.23 MHz/torr at 218 K.
The tropospheric‐stratospheric mean zonal flow in winter
Authors: Quiroz Roderick S.
Published: February 2008

Latitude‐height cross‐sections of the mean zonal geostrophic flow at 500–0.4 mbar (about 5–55 km) were derived for individual months of the winters 1975–1976 to 1978–1979. VTPR radiation data from NOAA satellites were used to obtain data above radiosonde heights. These cross sections are supplemented by time‐height cross sections at 65°N for 2‐month periods of stratospheric warming activity in each winter. Our mean latitude‐height cross section for winter shows marked differences from an earlier cross section published by Murgatroyd (1970), although some of the differences are due to the use of observed, rather than geostrophic, winds in the latter. The cross sections for individual months show a strong dispersal, between 25° and 65°N, of the latitude of maximum wind in the lower mesospheric jet, which often appears as a split system, in contrast to a single jet in Murgatroyd's representation. The modulation of the zonal wind pattern from month to month and winter to winter is evidently related to the cross‐tropopause propagation of planetary waves. The time‐height cross sections for stratospheric warming periods show wind minima and maxima with apparent upward and downward propagation across the tropopause. The minima, which include cases of reversed zonal flow (easterly), are associated with high‐latitude stratospheric warming and can be related further to the vertical propagation of planetary zonal height waves 1 and/or 2.
Sea ice, winter convection, and the temperature minimum layer in the Southern Ocean
Authors: Toole John M.
Published: February 2008

The structure of the near surface waters in the Southern Ocean, poleward of the Antarctic Polar Front but away from continental margins, is investigated with a three‐dimensional time‐dependent numerical model which resolves the annual sea ice cycle. The growth and decay of the ice field is predicted, using one of Semtner's (1976) thermodynamic ice models, in terms of specified atmospheric data and computed thermohaline characteristics of the ocean layers. The ice field is found to be sensitive to the lateral advection of heat by the oceanic circulation as well as vertical heat transports due to deep winter convection. The model treats the temperature minimum layer in the Southern Ocean as the remnant of a deep winter mixed layer which becomes capped by surface heating and precipitation in summer. The predicted thermohaline characteristics of the temperature minimum layer and the surface mixed layer are in good agreement with observations. Finally, the annual air‐sea heat exchange predicted by the model is discussed. The model's predicted area averaged heat loss experienced by the ocean south of the Atlantic Polar Front is much smaller than was previously estimated. This is attributed to errors in the southern region of the model domain. It is suggested that models, which include the interactions between sea ice and surface, deep and bottom waters along the continental margins, are needed to investigate this region.
Low‐frequency waves in the Ligurian Sea during December 1977
Authors: Crepon M. , Wald L. , Monget J. M.
Published: February 2008

Observations of low‐frequency waves in the Ligurian Sea in December 1977 are presented. From time series of thermal infrared images obtained by satellite NOAA 5, the mean wavelength and phase velocity are estimated. They are, respectively, 38 km and 18 cm s−1. These waves are analyzed as large‐amplitude baroclinic waves. Fairly good agreement is found with a two‐layer model.
Temperature dependence of the formation of sulfate aerosols in the stratosphere
Authors: Yue Glenn K. , Deepak Adarsh
Published: February 2008

Recent research has shown that aerosol particles in the stratosphere cannot be formed through homogeneous nucleation process. However, this conclusion is obtained by assuming the ambient temperature to be −50°C or −55°C, but in reality it is not unusual that in certain regions of the stratosphere temperature can be as low as −75°C or even lower. To assess the influence oftemperature on the formation of sulfate aerosols in the stratosphere, and to explore the possibility of forming new particles through homogeneous nucleation processes at certain regions where the temperature is extremely low, the classical nucleation theory is applied to calculate the temperature dependence of the characteristics and nucleation rates of sulfate aerosols in the binary H2SO4‐H2O vapor mixture. Our calculated results indicate that the number of new particles formed at a lower temperature is orders‐of‐magnitude larger than that at a higher temperature when the concentration of water and sulfuric acid vapors are kept constant. At stratospheric regions with low temperature there may exist large amounts of ultrafine particles that can hardly be detected by conventional methods.
Waveheight and wind speed measurements from the SEASAT radar altimeter
Authors: Fedor L. S. , Brown G. S.
Published: February 2008

Comparisons between the SEASAT radar altimeter inferred estimates of significant waveheight (SWH) and wind speed with buoy measurements for near overflights are presented. Details of the ‘calibration’ of SEASAT's measurement of σ0(0°) against those made by the GEOS‐3 radar altimeter are presented. The ‘onboard’ estimate of SWH is shown to be biased high by 0.5 m for SWH > 2 m. Comparisons of buoy measurements of SWH with altimeter waveform data processed by using the Fedor algorithm for 51 cases show a mean difference of 0.07 m with a standard deviation of 0.29 m over the range of 0.5–5 m SWH. The SEASAT inferred estimates of σ0(0°) are biased high by 1.6 dB relative to GEOS‐3 data. For 87 corrected comparisons with buoy measurements of wind speed, the mean difference is −0.25 m/s, and the standard deviation of the difference is 1.6 m/s over the range of 1–10 m/s wind speed. The numbers are very similar to GEOS‐3 data comparisons and thus provide a second corroboration of the waveheight and wind speed measurement capability of a short pulse spaceborne radar altimeter.
The SEASAT altimeter mean sea surface model
Authors: Marsh James G. , Martin Thomas V.
Published: February 2008

An 18‐day set of SEASAT altimeter data and precisely computed SEASAT ephemerides have been combined using accurate gridding techniques to compute global contour maps of the mean sea surface topography. The earth gravity models specially developed for SEASAT precision ephemeris computations (PGS‐S3 and PGS‐S4) have been used to calculate the ephemerides over this 18‐day time period. The altimeter data have an rms agreement of 111 cm with the SS3 mean sea surface computed using the PGS‐S3 ephemerides and 70 cm with the SS4 mean surface computed using the PGS‐S4 ephemerides. Comparisons with the GEM 10B 1°×1° detailed gravimetric geoid have rms differences of 2.8 m, while comparisons with a global mean sea surface computed from GEOS 3 altimeter data have rms differences of 1.3 m for the SS3 surface and 1.1 m for the SS4 surface.
A model of the Antarctic sink for stratospheric water vapor
Authors: Douglass Anne R. , Stanford John L.
Published: February 2008

Model calculations have been performed to quantitatively estimate the amount of stratospheric H2O removed by freeze out during the winter in the Antarctic region. The model uses realistic temperature and wind fields based on Hartmann's Nimbus 5 temperature grids. For the 1973 Antarctic winter stratosphere, initial water vapor mixing ratios of 2.7 and 3.0 ppmm lead to removal of 1.6 and 2.7×1010 kg H2O from the lower stratosphere. This annual sink magnitude is small, representing about 2% of the total stratospheric H2O burden and about 10% of the apparent sink identified by Ellsaesser (1974). However, a sink of this magnitude is close to the lower rate estimates of water produced in the stratosphere by methane oxidation. The sink is not large enough to balance additional, proposed water vapor sources.
Sea ice motion in response to geostrophic winds
Authors: Thorndike A. S. , Colony R.
Published: February 2008

It is an old rule‐of‐thumb that sea ice moves with a speed of about 2% of the surface wind and about 45° to the right of the wind. A similar relationship between the ice velocity and the geostrophic wind is examined here. It is found that only about half of the long‐term (several month) average ice motion is directly related to the geostrophic wind, the other half being due to the mean ocean circulation. On shorter time scales and in all seasons, more than 70% of the variance of the ice velocity in the central Arctic Ocean is explained by the geostrophic wind. Within about 400 km of the coasts the geostrophic wind is less successful in explaining the ice motion. The spatial variations in ice velocity are also partly explained by the geostrophic wind. About half of the variance in the large‐scale ice vorticity and shear are accounted for. On the other hand, none of the large‐scale ice divergence can be explained by the wind. The long‐term average ocean current is estimated by subtracting the share of the ice motion caused by the wind from the total ice motion.
The composition of precipitation in remote areas of the world
Authors: Galloway James N. , Likens Gene E. , Keene William C. , Miller John M.
Published: February 2008

The Global Precipitation Chemistry Project collects precipitation by event to determine composition and processes controlling it in five remote areas. Compositions (excluding sea‐salt) at St. Georges, Bermuda, were primarily controlled by anthropogenic processes; compositions and acidities at San Carlos, Venezuela, Katherine, Australia, Poker Flat, Alaska, and Amsterdam Island were controlled by unknown mixtures of natural or anthropogenic processes. Precipitation was acidic; average volume‐weighted pH values were 4.8 for Bermuda; 5.0, Alaska; 4.9, Amsterdam Island; 4.8, Australia; 4.8, Venezuela. Acidities at Bermuda and Alaska were from long‐range transport of sulfate aerosol; at Venezuela, Australia, and Amsterdam Island, from mixtures of weak organic and strong mineral acids, primarily H2SO4. Relative proportions of weak to strong acids were largest at Venezuela and lowest at Amsterdam Island. Weak and strong acids were from mixtures of natural and anthropogenic processes. Once contributions from human activities were removed, the lower limit of natural contributions was probably ≥pH 5.
O2 absorption cross sections (187–225 nm) from stratospheric solar flux measurements
Authors: Herman J. R. , Mentall J. E.
Published: February 2008

The absorption cross sections of molecular oxygen are calculated in the wavelength range from 187 to 230 nm from solar flux measurements obtained within the stratosphere. Within the Herzberg continuum wavelength region the molecular oxygen cross sections are found to be about 30% smaller than the laboratory results of Shardanand and Rao (1977) from 200 to 210 nm and about 50% smaller than those of Hasson and Nicholls (1971). At wavelengths longer than 210 nm the cross sections agree with those of Shardanand and Rao. The effective absorption cross sections of O2 in the Schumann‐Runge band region from 187 to 200 nm are calculated and compared to the empirical fit given by Allen and Frederick (1982). The calculated cross sections indicate that the transmissivity of the atmosphere may be underestimated by the use of the Allen and Frederick cross sections between 195 and 200 nm. The ozone column content between 30 and 40 km and the relative ozone cross sections are determined from the same solar flux data set. The calculated ozone absorption cross sections agree with those of Inn and Tanaka (1959) and Bass and Paur (1981) to within 3%.
Nitric acid column densities over Antarctica
Authors: Williams Walter J. , Kosters John J. , Murcray David G.
Published: February 2008

Nitric acid column densities derived from atmospheric infrared spectral emission data measured from the NSF USARP C130 research aircraft in the Spring of 1978 are presented, summarized by latitude. An increase of the column density with latitude is noted, along with a longitudinal asymmetry in the latitudinal dependence. Column densities range in values from 1.2±0.2×1020 molecules m−2 at 53°S latitude to 3.4±0.7×1020 molecules m−2 at 89°S latitude. Also, the liquid helium cooled spectral radiometer used to obtain the data and the associated calibration procedures are described.
Continental shelf waves of diurnal period along Vancouver Island
Authors: Crawford W. R. , Thomson R. E.
Published: February 2008

Recent surveys of tides and currents on the continental shelf along the west coast of Vancouver Island have shown the diurnal tidal currents to be larger than the semi‐diurnal by a factor of 2–4, although the ratio (K1 + O1)/(M2 + S2) for the tidal heights is only 0.6. We attribute the diurnal currents to continental shelf waves, and show that the continental shelf and slope off Vancouver Island allow first mode barotropic shelf waves at the diurnal frequency. The tidal heights and deep water currents of K1 and O1 frequency behave as progressive Kelvin waves with height 43 cm at shore, and currents of 1–2 cm/s. The observed shelf waves at these frequencies have amplitudes at shore of 5 and 3 cm, and currents of order 10 and 6 cm/s, respectively. The Kelvin and shelf waves are in phase near Ucluelet and out of phase near Kyuquot, as determined by both current meter and shore tide gauge observations. Observed wavelengths are longer than predicted for a barotropic shelf wave, in accordance with the expected influence of stratification.
Variability of the near‐surface residual current in the lower St. Lawrence estuary
Authors: El‐Sabh M. I. , Lie H.‐J. , Koutitonsky V. G.
Published: February 2008

Current measurements of 1‐ and 4‐month duration from May 1979 taken at 10 stations in the lower St. Lawrence estuary were subject to time series analysis. We find that the spectral energy density of the near‐surface current in the sub‐inertial frequency range is comparable to the energy concentrated in the semi‐diurnal frequency band. The strong residual current decreases rapidly with depth while the tidal current is more or less uniform from surface to bottom. A cross‐spectral analysis showed that the longshore current at a station near the south shore was negatively correlated to the current at a north shore station with high coherence in the period range greater than 7 days. Evidence was found for the existence of a cross‐channel current at stations in the center of the channel. The near‐surface circulation system in the area can be classified into three types of patters: (1) one anticyclonic eddy centered between the estuary‐gulf boundary and the Baie‐Comeau cross‐section (region I) accompanied by a cyclonic eddy located to the landward between the two cross sections at Baie‐Comeau and Pointe‐au‐Père (region II), (2) a cyclonic eddy in region I with an anti‐cyclonic eddy in region II, and (3) the transition phase between phases 1 and 2. The intensity of these eddies and cross‐channel currents is related to sea level changes in the estuary.
Volcanic output of long‐lived radon daughters
Authors: Lambert G. , Ardouin B. , Polian G.
Published: February 2008

The concentrations of long‐lived radon daughters have been measured in the exhausts of 11 volcanoes throughout the world. More particularly, the 210Po activities measured were 105–106 times higher than in a typical atmosphere. A total volcanic 210Po output of 5×104 Ci/yr can be estimated by balancing the total deposition (9×104 Ci/yr), the atmospheric production (3×104 Ci/yr), and the other extra sources (1×104 Ci/yr) of this nuclide. Therefore it seems possible to normalize the volcanic production of volatile elements to this 210Po output.