bluuebunny/crossref_metadata_2025 huggingface dataset:
Mafic inclusions from the Glenbog and Blue Gum granite suites, southeastern Australia
Authors: Chen Y. D. , Price R. C. , White A. J. R. , Chappell B. W.
Published: February 2008

Mafic inclusions from the I‐type granites of the Glenbog and Blue Gum suites of the Lachlan Fold Belt of southeastern Australia are less than 1 m and mostly less than 10 cm. in size and are generally in sharp contact with the surrounding host granites (unless otherwise stated the term “granite” is used in this paper in the general sense to include granite senso stricto, adamellite, granodiorite, tonalite, etc.). Although some inclusions are irregular in shape, the majority have an elliptical or circular outline when viewed on exposed surfaces. Rounded and subrounded individuals outnumber those with an angular appearance. Abundances of inclusions in seven plutons of the Glenbog and Blue Gum suites range from about 6% to less than 0.1%. Their abundance is negatively correlated with the SiO2 content of the host rock. Mafic inclusions contain the same mineral species as the host granite but plagioclase and hornblende are more abundant, and quartz and K‐feldspar are less abundant in inclusions. Mafic inclusions all contain more than 54% SiO2 and are mostly intermediate in composition. The abundances of many elements in the mafic inclusions follow those of that element in the host granites. Sr and Nd isotopic compositions in both the granites and the inclusions are similar and relatively evolved. Various models for the origin of the inclusions are considered. It is concluded that, of those considered, the only model capable of explaining all data is that the inclusions represent fragments of more refractory source material that were carried up with the magma. It is suggested that this more refractory character resulted from a lesser degree of hydration of the source rocks of the magmas, prior to partial melting.
Direct measurement of the effective pressure law: Deformation of joints subject to pore and confining pressures
Authors: Boitnott G. N. , Scholz C. H.
Published: February 2008

When describing the deformation of poro‐elastic materials subject to pore pressure (PP) and confining pressure (PC), the concept of effective pressure is commonly used. In such a description the deformation is described in ternis of a single stress parameter, the effective stress (PE). Experimental studies which attempt to describe the effective pressure law are troubled by the fact that deformation of geologic materials invariably exhibits loading path dependence (hysteresis). Properties which exhibit hysteresis are not easily described by a single stress state variable and hence the concept of effective pressure becomes clouded. Therefore, the effective pressure law here is formulated to describe the relative effects of pore and confining pressure on a given property, with specific attention to the loading path. Here we develop an experimental technique for measuring the effective pressure law which is useful for many properties of interest, including those that are highly nonlinear and exhibit common types of hysteresis. Applying this method in an experimental study of the effective pressure law for joint closure, we experimentally derive an effective pressure law which describes the values of pore and confining pressure consistent with a given joint closure for a loading path of constant closure. The study can be viewed as an attempt to include both pore and confining pressure in a single constitutive law for joint closure. The constant closure loading path is such that the measurement is not affected by hysteresis caused by joint closure. The results provide insight into the microgeometrical and micromechanical properties of joints. The data are not consistent with a simple extension of commonly used linear elastic constitutive models for joint deformation which have compared favorably with experiments in the absence of pore pressure. For smooth lapped glass joints, the effective pressure relation is found to be dependent on the local joint stiffness, with the relationship between the effective pressure law and the local joint stiffness being insensitive to the measured surface topography. Similar measurements on lapped and fractured rock provide some constraints on the effective pressure behavior of jointed rock.
Fundamental thermodynamic relations and silicate melting with implications for the constitution of D″
Authors: Stixrude Lars , Bukowinski M. S. T.
Published: February 2008

We describe fundamental thermodynamic relations (Helmholtz free energy as a function of volume and temperature) for solids and liquids, simple physically based expressions which contain all thermodynamic information about a system. The solid fundamental relation consists of Debye and Birch‐Murnaghan finite‐strain theory combined in the Mie‐Grüneisen framework. The liquid fundamental relation is derived by taking the high‐temperature limit of the solid expression. We derive the liquid equation of state, which contains only four parameters, from the liquid fundamental relation and show that it successfully describes measurements of liquid alkali metals, water, and liquid diopside over a wide range of pressure and temperature. We find optimal fundamental relation parameters for diopside, enstatite, ilmenite, and perovskite and find the solid relation to be in excellent agreement with data, including heat capacities, thermal expansion, and MgSiO3 phase equilibria. We then combine the liquid and solid fundamental relations to calculate the melting curves of diopside, enstatite, and perovskite, which are found to be in excellent agreement with experiment. All predicted melting curves have dT/dP slopes which decrease steadily with pressure, eventually becoming negative because of liquid‐crystal density inversion. Our predicted melting temperature of perovskite in the D″ region (3750 K) at the base of the mantle is thousands of degrees lower than previous estimates, yet it is consistent with experimental data. The predicted melting curve, although consistent with the lack of widespread melting in the lower mantle, is much lower than recently proposed geotherms in the D″ layer at the base of the mantle. By combining our results with seismic observations of the deep mantle, we propose that the D″ layer consists of magnesiowüstite and silica in the form of stishovite or its recently discovered high‐pressure modification.
A numerical model of volatile behavior in nonwelded cooling pyroclastic deposits
Authors: Miller Timothy F.
Published: February 2008

The solution of the governing transport equations for transient volatile behavior in a cooling pyroclastic deposit reveals dominant mechanisms that control cooling and degassing. The numerical model and algorithm presented here are time accurate and suitable for operation on a personal computer. This model takes into account the combined effects of cooling and low volatile outfluxing on the pressure, temperature, and volatile mass content in a deposit. Sample deposit simulations compare favorably with observations made by Kozu (1934) and Kienle and Swanson (1980). Other exemplary calculations of 20‐ and 40‐m thick pyroclastic deposits indicate that the time required for total volatile outflux (approximately 21 and 83 days, respectively) is small compared with that required for the cooling effects of the upper and lower margins to come in contact (in excess of 70 and 265 days, respectively). The thermal behavior of the modeled deposits appears to be dominated by diffusive heat transfer, while the pressure field and volatile content within each sheet are dominated by hydrodynamic effects.
Mantle flow tectonics: The influence of a ductile lower crust and implications for the formation of topographic uplands on Venus
Authors: Bindschadler Duane L. , Parmentier E. Marc
Published: February 2008

Convective flow within the interiors of terrestrial planets is a primary source of large‐scale topographic and tectonic features. We treat the crust and mantle as a layered viscous half‐space and find solutions for flow driven by a buoyancy force distribution within the mantle and by relief at the surface and crust‐mantle boundary. The crust initially responds to mantle upwelling with uplift, but continued flow causes significant crustal thinning and subsidence. Downwelling leads to initial subsidence and subsequent crustal thickening and surface uplift. Changes in crustal thickness are driven by (1) vertical normal stresses due to mantle flow and (2) shear coupling of horizontal mantle flow into the crust. The degree and time scale of crustal deformation are sensitive to crustal thickness and viscosity and the presence of elastic layers in the upper crust and mantle. Deformation can occur on time scales less than several hundred million years for reasonable values of these parameters. Strong or elastic upper crustal layers enhance crustal thinning or thickening, while large viscosity contrasts between the lower crust and upper mantle or elastic mantle layers tend to diminish deformation. For time‐dependent mantle flow due to a rising or sinking diapiric body, crustal deformation depends upon the ratio of diapir radius to crustal thickness, and the ratio of crustal to mantle viscosity. A sinking diapir can lead to crustal thickening, elevated topography, and a specific sequence of time‐varying deformation, While regions such as Beta Regio have long been suggested to result from convective upwelling in the Venus mantle, we suggest that a mantle downwelling origin is consistent with many of the characteristics of the compressional mountain ranges of western Ishtar Terra.
Mechanical anisotropy of gneiss: Failure criterion and textural sources of directional behavior
Authors: Gottschalk Richard R. , Kronenberg Andreas K. , Russell James E. , Handin John
Published: February 2008

The mechanical anisotropy of Four‐mile gneiss has been investigated in a series of uniaxial and triaxial, compression and extension experiments performed at confining pressures Pc up to 400 MPa, constant strain rates ε from 1.6×10−6 to 1.5×10−4 s−1, and temperatures T from 25° to 800°C on cylindrical and notched samples oriented with respect to foliation (S) and lineation (L). Differential stresses measured both at the onset of yielding and at failure vary with specimen orientation, with maximum compressive strengths exhibited by samples cored perpendicular to S and minimum strengths exhibited by samples cored at 45° to both S and L. While failure strengths are influenced most strongly by the orientation of S, they appear to depend upon the orientation of L as well. An orthorhombic failure criterion, generalized from a nonlinear Mohr‐Coulomb relation, has been considered with quadratic and linear stress terms resembling those of invariants J2 and I1, respectively, and material parameters estimated by nonlinear regression methods. Satisfactory fits were achieved for results at T = 25°C as well as T = 700°C. Fracture strengths are relatively insensitive to changes in T and ε and the anisotropy exhibited at T = 700°C is remarkably similar to that measured at T = 25°C. Relatively small reductions in strength observed at elevated temperatures are probably due to the influence of thermally induced microcracks. Mechanisms of deformation and sources of anisotropy have been identified by examining microstructures developed in deformed specimens and observing their relationships to those fabric elements initially present in the starting material. Throughgoing shear fractures developed in samples shortened in all orientations with respect to S and L by the coalescence of microcracks in feldspar and quartz grains, as reported for isotropic granites. However, inelastic strains within mica grains were accommodated by slip, frictional sliding, and kinking, and deformation of favorably oriented micas appears to have led to local stress concentrations in neighboring phases that result in nucleation of tensile microcracks. Both S and L are defined by the preferred orientations of micas, and a simple model involving crack nucleation around oriented mica grains is proposed to explain the anisotropy observed.
High‐temperature raman spectroscopy of SiO2 and GeO2 Polymorphs: Anharmonicity and thermodynamic properties at high‐temperatures
Authors: Gillet Philippe , Le Cléac'h Andrée , Madon Michel
Published: February 2008

The temperature dependence of the room pressure Raman spectra of the GeO2 (hexagonal and tetragonal) and SiO2 (quartz, coesite, and stishovite) polymorphs is presented. Several transformations upon heating are reported: α‐β quartz, coesite‐cristobalite, stishovite‐silica glass (with Si in four‐fold coordination). For all the compounds, Raman frequencies decrease linearly with temperature and the measured shifts are used in conjunction with available high‐pressure Raman data to calculate for each compound intrinsic mode anharmonicity through the parameter ai=(∂lnVi/∂T)v. In quartz the modes related to the α‐β transition (128 and 207 cm−1 modes) are highly anharmonic (ai=−20×10−5 K−11). In coesite many bands are unaffected by temperature and only two modes (77 and 116 cm−1) show significant anharmonic behaviour. Tetragonal GeO2 and stishovite behave similarly under temperature. Vibrational modeling of the specific heat and entropy, including anharmonic corrections deduced from the ai parameters, are presented and compared to available calorimetric measurements. For the GeO2 polymorphs the agreement between calculated and measured values is within 1–3% in the temperature range 100 to 1500 K. For quartz the agreement is similar over the range 50–850 K. For coesite and stishovite the models reproduce existing low temperature measurements. High‐temperature values of Cp and entropy are proposed for coesite and stishovite.
The high‐pressure triple points of iron and their effects on the heat flow from the Earth's core
Authors: Anderson Orson L.
Published: February 2008

The triple point joining the ϵ (hcp), and γ(fcc), liquid phases of iron has been estimated by a number of authors, using (in the words of Birch (1972)) “speculative projections.” Three of these projections would place this triple point at or below 100 GPa, while the third locates it at 280 GPa. The methods used in each case are quite interesting historically, because they reveal the state of the art in iron physics and its application to geophysics at the times of the respective publications. The subject is not closed yet, and no doubt future publications will point out new trip1e‐point locations.
Kinematic modeling of cross‐sectional deformation sequences by computer simulation
Authors: Contreras Juan , Suter Max
Published: February 2008

We derive a kinematic algorithm which permits simulation of postulated cross‐sectional deformation sequences in sedimentary rocks affected by faulting, fault‐related folding, and simple shear. The transformations are to a more deformed state and are formulated analytically in terms of the less deformed configuration (forward modeling, Lagrangian description). The medium is subdivided into domains of constant dip and homogeneous displacement vector fields which are delimited by the axial planes of the fault inflections. The displacement trajectory is of constant length for all the displaced particles throughout the medium and parallel to the underlying active fault segment. As a consequence, the deformation path is continuous but not smooth and causes an angular style of parallel folding, except at the deformation front where the layer thickness is not conserved. The inhomogeneity of the displacement vector field across axial planes introduces longitudinal and angular shear strains, whereas the area of the medium remains constant. These strains, which are superposed on the externally applied simple shear, make the mapping transformation unconformal. We define the stratigraphic layering of the undeformed medium by an approximating body of finite quadrilateral elements, evaluate the defined displacement functions for the grid nodes, and graph the deformed mesh. Eventually, we create with the algorithm synthetic deformation sequences for simple boundary conditions and try in a specific case study to match the resulting synthetics with the available observational and experimental data.
The rain parameter diagram: Methods and applications
Authors: Ulbrich Carlton W. , Atlas David
Published: February 2008

A rain parameter diagram is presented which displays the relationships between all rainfall parameters defined in terms of an exponential drop size distribution. Special emphasis is given to remotely measurable quantities such as radar reflectivity, microwave attenuation, and optical extinction. Although an exponential distribution is used to construct the diagram, it is shown to have general application for arbitrary size distributions and for a wide variety of rainfall‐related problems. Some of the problems are (1) analysis of the sources of error which result from the use of empirical rainfall relations, (2) depiction of the physical differences between different types of rainfall and of the similarity between all empirical relations which apply to the same type of rainfall, and (3) determination of the accuracy with which remote measurements must be made to obtain accurate measurements of rain parameters. A set of overlays is shown for four common radar wavelengths and four temperatures which display the relationships between microwave attenuation and the other rainfall parameters. Methods are discussed by which these diagrams can be used to determine rainfall parameters remotely in dual‐measurement techniques. The diagrams can also be used to find the errors in these rainfall parameters which result from errors in the two quantities involved in the dual‐measurement technique.
An estimate of the vertical mixing due to salt fingers based on observations in the North Atlantic central water
Authors: Schmitt Raymond W. , Evans David L.
Published: February 2008

Recent theoretical work suggests that salt fingers have sufficiently rapid growth rates in much of the thermocline to produce significant vertical fluxes of heat and mass, even in an active internal wave field. Using laboratory determinations of the
power law for the salt flux we have estimated the salt flux at depth for several CTD stations in the central water of the North Atlantic by assuming the fingers to be intermittently active on the high‐gradient sheets in the thermocline. The flux is found to be comparable to the surface input of salt due to evaporation. This implies a release of energy by the falling out of salt, comparable to the rate of work done by the wind on the mean circulation, and supports the model of Stern (1969b). Salt fingers transport heat and mass at different rates, and thus the usual concept of an ‘eddy diffusivity’ is invalid when salt fingers make a major contribution to the vertical mixing processes.
Measurements and models of fine structure, internal gravity waves, and wave breaking in the deep Ocean
Authors: Eriksen Charles Curtis
Published: February 2008

Measurements of horizontal and vertical current by propeller cluster current meters and temperature by thermistors mounted on a rigid array 8 m high and 20 m long moored in the oceanic main thermocline near Bermuda are interpreted in terms of thermocline‐trapped internal wave modes in the presence of temperature and velocity fine structure. The array was deployed roughly 250 m off the sloping bottom in water roughly 900 m deep on three occasions. Two‐turning‐point uniformly valid asymptotic solutions to the internal wave equation are developed to describe the wave functions. Mode decay beyond the turning point in depth or frequency produces a sharp cutoff in vertical current spectra above the local buoyancy frequency N(z). An internal wave wave number‐frequency spectral model E( α,ω) = E(ω/N0)−2(α/α0)−2 describes vertical current spectra and ratios of potential energy to horizontal kinetic energy. The red wave number shape suppresses peaks in both these quantities at frequencies near N(z). A dip in the vertical current spectra at 0.5 cph not predicted by the model appears related to the bottom slope. Temperature fine structure is modeled as a passive vertical field advected by internal waves. Quasi‐permanent fine‐scale features of the stratification and vertically short internal waves are indistinguishable in this study. The model of McKean [1974] is generalized to include fine structure fields specified by their vertical wave number spectra. In addition to the trapped internal wave model, moored temperature spectra, temperature vertical difference spectra, and coherence over vertical separations are described by using a fine structure vertical wave number spectrum PT(k) ATk−5/2; which agrees with other spectra made by using vertical profiling instruments in the range 0.1–1.0 cpm. Horizontal current fine structure is also modeled as a passive field advected by vertically long internal waves. The model describes moored horizontal current spectra (least successfully at frequencies near N(z)) and finite difference vertical shear spectra. Contours of temperature in depth versus time indicate possible mixing events. These events appear concurrently with high shear and Richardson numbers 0.25 ≲ Ri ≲ 1.0. Over a 7‐m vertical separation a cutoff in Ri at 0.25 is observed, indicating possible saturation of the internal wave spectrum. Spectra of finite difference approximations to shear and buoyancy frequency are dominated by fine structure contributions over nearly the entire internal wave range, suggesting that breaking is enhanced by fine structure/Breaking appears equally likely at all frequencies in the internal wave range.
Fronts on the continental shelf
Authors: Simpson J. H. , Allen C. M. , Morris N. C. G.
Published: February 2008

A well‐defined class of fronts occurring in the shelf seas around the United Kingdom during the summer months marks the boundary between stratified and vertically mixed regimes. The occurrence of these fronts may be interpreted in terms of the distribution of available turbulent kinetic energy from the tidal currents and wind stress and the buoyancy flux input at the surface. The principal parameter controlling stratification is the ratio of the water depth to a Monin‐Obhukov length determined by the tidal velocity. A corresponding parameter based on the wind stress is also found to contribute significantly in a combined model of tide and wind mixing. Vertical sections perpendicular to the front by undulating CTD indicate a strongly baroclinic region with horizontal temperature gradients of ∼1°C/km, which imply strong flows parallel to the front. Drogue observations show that nontidal velocities of ∼10 cm/s occur in the vicinity of the fronts but the flow regime is apparently complicated by large‐scale (∼25 km) instabilities which are clearly manifest in satellite infrared imagery and airborne radiation thermometer surveys. There is also indirect evidence for vertical motions suggesting that both upwelling and down‐welling occur in the frontal zone.
Tidal fronts on the shelf seas around the British Isles
Authors: Pingree R. D. , Griffiths D. K.
Published: February 2008

A numerical model is used to derive the Simpson‐Hunter stratification parameter on the shelf seas surrounding the British Isles. Positions of predicted fronts are compared with structures observed in infrared satellite images and the measurements of sea surface temperature recorded on a cruise around the British Isles. The numerical model predicts the stability of the frontal systems, and baroclinic instability is suggested as the main candidate for cross‐frontal mixing.
The anatomy of the Antarctic polar front in the Drake Passage
Authors: Joyce Terrence M. , Zenk Walter , Toole John M.
Published: February 2008

An intensive three‐dimensional survey of the Antarctic Polar Front was made in the Drake Passage in March 1976. The front, which was imbedded within one of the high‐velocity cores of the circumpolar current, is viewed as a water mass boundary demarking the northern extent of near‐surface antarctic waters. Within the front, water masses are observed to intrude, one above the other, with characteristic vertical scales of 50–100 m. The intrusions are horizontally anisotropic, being elongated in the alongstream direction and constrained primarily to the upper 800 m of the front. The spatial and temporal persistence of the variability is examined through the analysis of continuous vertical profiles of horizontal velocity, temperature, salinity, and oxygen with discrete sampling of nutrients. Analysis of the velocity data showed the mean current flowing to the NNE with speeds of the order of 30–40 cm s−1 in the upper 600 m, with temporal variability over a 28‐hour ‘yo‐yo’ due primarily to internal gravity waves. The thermohaline variability was not internal wave induced but rather was associated with nearly isentropic advection of different water masses across the front. Cold fresh and warm salty intrusions did not conserve potential density, however, and double‐diffusive transfers are strongly suggested as being crucial to an understanding of the dynamics of the intrusions. Applying a model (Joyce, 1977) for lateral mixing we estimate poleward temperature and salinity fluxes due to interleaving of 0.086°C cm s−1 and 0.069‰ cm s−1, respectively. If these values are typical, interleaving could play a significant role in large‐scale balance of salt and, to a lesser extent, heat for the Southern Ocean.
Geostationary satellite observations of Gulf Stream meanders: Infrared measurements and time series analysis
Authors: Maul George A. , deWitt P. Webb , Yanaway Alan , Baig Stephen R.
Published: February 2008

The infrared capabilities of the Geostationary Operational Environmental Satellite (Goes) are analyzed to obtain multiyear time histories of Gulf Stream meanders. Radiative transfer calculations using monthly mean profiles of atmospheric temperature and moisture are shown to overestimate cloud‐free equivalent soundings by 2–5 K. A simple relation is derived between temperature at the satellite, sea surface temperature, and transmissivity of the atmosphere at 11.6 μm, which allows an observer to determine if a known sea surface temperature gradient is observable from Goes knowing only the precipitable water content along the slant path to the spacecraft. More than 2 years of Goes observations of Gulf Stream meanders are analyzed as a randomly spaced time series using least squares spectral analysis; the dominant periods in the spectra, based on 1976–1978 data, are 250,65, and 10 days in the Gulf of Mexico; 30 and 6 days off Onslow Bay, North Carolina; and 45 and 5 days off New England. A summary of the meanders between the Yucatan Strait and the Grand Banks shows that the largest latitudinal variability is associated with the Gulf Loop Current. Comparison of meander periods with least squares spectra of historical Florida Current transports suggests that meanders in the Gulf of Mexico are related to variability with 4‐ to 16‐day and 40‐ to 100‐day periods in the flow.
Some concomitant regional anomalies associated with hemispherically averaged temperature variations
Authors: Namias Jerome
Published: February 2008

This paper presents some ideas based upon studies of historical data, intuition, and extensive synoptic experience—ideas which may be relevant to estimates of the climatological impact of a projected CO2 increase over future decades. Reliable 1000‐ to 700‐mbar thickness data are used to demonstrate possible regional effects associated with global warming. Global thickness values are shown to be correlated with hemispheric mean temperatures given by several investigators, and it is believed that use of these thicknesses is more appropriate to large‐scale circulation studies than is surface temperature. It is shown that the mean temperature of the entire contiguous United States is not highly correlated with the northern hemisphere mean. Precipitation over the United States is not well correlated with global mean temperature either, although there is a suggestion that in summer, heavier precipitation occurs when hemispheric mean temperatures are low. Two scenarios for a moderate CO2‐induced increase in temperature, a general hemispheric warming and a warming which is most intense in the Arctic, are examined by analysis of the warmest recent winters over the hemisphere and over the Arctic, respectively. Both cases are characterized by high‐latitude blocking, relative cooling at lower latitudes, and strong regionalization of thickness anomaly patterns. A potential moderating influence by the oceans through increased CO2 absorption is discussed. Comparisons are made between latitudinal profiles of recent warm years and the results of the Manabe‐Wetherald model studies. Overall, it appears that the climatic effects of CO2 variations may be much more complex than is often surmised, so it is not wise to draw inferences of regional anomalies from hemispheric means or latitudinal profiles.
Simultaneous spectroscopic measurements of stratospheric species: O3, CH4, CO, CO2, N2O, H2O, HCl, and HF at northern and southern mid‐latitudes
Authors: Farmer C. B. , Raper O. F. , Robbins B. D. , Toth R. A. , Muller C.
Published: February 2008

Near‐infrared solar absorption spectra have been recorded in the course of balloon flights from Palestine, Texas, (32°N latitude) in May 1976, and Broken Hill, Australia, (30°S latitude) in March 1977. The northern flight was made at a float altitude of 37 km and covered the spectral region from 1800 cm−l to 3600 cm−1, which encompasses infrared transitions of O3, CH4, CO, CO2, N2O, H2O, and HCl. The flight in the southern hemisphere, from a float altitude of 39 km, covered the spectral region from 2800 cm−l to 4500 cm−1, which includes useful transitions for all of the above gases (with the exception of CO) and encompasses as well the 1‐0 fundamental band for HF. Both sets of spectra were acquired at sunset by using a high‐resolution (0.13 cm−1) Michelson interferometer. The simultaneous profiles of concentration derived from the spectra for the individual gases covered in each flight are presented and discussed. While the results show few differences between the profiles at the northern and southern latitudes, there are several aspects of general importance; these include lower values for stratospheric CO than had previously been reported (i.e., ∼10 ppbv), and water vapor profiles in both hemispheres showing an increase with altitude considerably in excess of that to be expected from CH4 oxidation alone. The shape of the profile for HF was found to be consistent with model predictions, but the HF concentrations were lower by a factor of 3 or 4 than those predicted.
Ocean chlorophyll studies from a U‐2 aircraft platform
Authors: Kim Hongsuk H. , McClain Charles R. , Blaine Lamdin R. , Hart William D. , Atkinson Larry P. , Yoder James A.
Published: February 2008

Chlorophyll gradient maps of large ocean areas were generated from U‐2/OCS data obtained over test sites in the Pacific and the Atlantic Oceans. The delineation of oceanic features using the upward radiant intensity relies on an analysis method which presupposes that radiation backscattered from the atmosphere and the ocean surface can be properly modeled by using a measurement made at 778 nm. The calculation of atmospheric radiance was performed by using a method developed by J. V. Dave. An estimation of the chlorophyll concentration is performed by properly ratioing radiances measured at 472 and 548 nm after removing the atmoshperic effects. The correlation between the remotely sensed data and then situ surface chlorophyll measurements has been validated in two sets of data. The results show that the correlation between the in situ measured chlorophyll and the derived quantity is a negative exponential function, and the correlation coefficient was calculated to be −0.965.
Relationships between extinction, absorption, backscattering, and mass content of sulfuric acid aerosols
Authors: Pinnick R. G. , Jennings S. G. , Chýlek Petr
Published: February 2008

Linear relationships between aerosol extinction, absorption, backscatter, and mass content are derived for polydispersions of sulfuric acid aerosols. These relationships are independent of the form of the size distribution and are a consequence of approximating the corresponding Mie efficiency factors (the extinction efficiency Qe, the absorption efficiency Qa, and the backscatter gain G) by linear functions of the particle size parameter x. The relationships are valid only at particular wavelengths that depend on the range of particle sizes present in a particular polydispersion. For example, at a wavelength λ = 0.694 μm the relation between aerosol backscatter coefficient σbs(m−1 sr−1) and mass content M (g m−3) is σbs = 0.048M for 75% sulfuric acid (25% water) aerosol, under the restriction that particles in the polydispersion have sizes not exceeding about 1.5 μm in radius. Possible applications of the relationships are (1) inference of path‐integrated mass content of sulfuric acid aerosol (for example, the clouds of Venus) from an infrared laser transmission measurement through the aerosol cloud, (2) determination of sulfuric acid aerosol mass content at a particular point in an aerosol cloud from aerosol absorption measurements at that point with a CO2 (λ = 10.6 μm) laser spectrophone, (3) inference of path‐integrated stratospheric aerosol mass from aerosol extinction measurements made by solar occultation for wavelengths λ = 0.55 and 1 μm, and (4) inference of vertical profiles of stratospheric aerosol mass from ruby lidar (λ = 0.694 μm) backscatter measurements.
The behavior of ozone near the stratopause from two years of BUV observations
Authors: McPeters Richard D.
Published: February 2008

Two years of Nimbus 4 backscattered ultraviolet data have been recalibrated and reprocessed. A Laplace transform inversion was applied to radiances at 2876 Å and below for 560,000 individual scans for the period April 1970–May 1972. The behavior of ozone near 50 km as a function of time, latitude, and longitude is presented. The high‐latitude 1‐mbar ozone mixing ratio is maximum at the winter solstice, about 10μg/g and is minimum at the summer solstice, about 4μg/g. Below 30° latitude the ozone is fairly constant at 4μg/g. Ozone variability is large in winter and spring and small in summer and fall.
Lightning source locations from VHF radiation data for a flash at Kennedy Space Center
Authors: Rustan P. L. , Uman M. A. , Childers D. G. , Beasley W. H. , Lennon C. L.
Published: February 2008

A comprehensive study of a three‐stroke lightning flash that struck the 150‐m weather tower at Kennedy Space Center (KSC) was recently reported by Uman et al. (1978). Here we supplement that study by presenting three‐dimensional locations of the sources of VHF (30–50 MHz) radiation generated by the KSC flash. These locations were obtained by measuring with the KSC lightning detection and ranging (LDAR) system the difference in the time of arrival (DTOA) of radiated pulses at four ground stations and then by calculating the locations from the DTOA data. The DTOA data were obtained via a newly developed computer‐implemented multiple time series analysis which uses cross‐correlation and pattern recognition techniques. About 48,000 sequential VHF sources were located during the flash. We compared these locations with correlated wide band electric field records to provide a better understanding of the physics of the following discharge phases: preliminary breakdown, stepped leader, return strokes, dart leader, stepped‐dart leader, J changes, solitary pulses, and intracloud discharge. Some of the more interesting new results obtained follow: before the stepped leader preceding the first return stroke, there was a primarily vertical discharge in the cloud between a height of 7.2 and 5.1 km. This preliminary breakdown has uniquely different VHF characteristics from those of the stepped leader which followed and was not accompanied by significant electric field change as was the stepped leader. The stepped leader propagated downward from the bottom of the preliminary breakdown. The only significant VHF radiation during the dart leader preceding the second return stroke came from within the cloud. The third return stroke was initiated by a stepped leader which propagated from about 8 km height, the bottom of the previous J process, down to about 3.3 km where it apparently joined the channel of the previous return stroke and became a dart leader. The VHF source locations during the two J changes were associated with the lowering of about 3 C of negative charge at velocities of about 2×105 m/s along primarily vertical paths from a height of about 13.7 to about 7.9 km for the first J change and from 11.2 to 7.3 km for the second J change. During the second J change and before and during the intracloud discharge following the three strokes to ground, discharges which appear on the VHF record as isolated or solitary pulses propagated upward 3–8 km at velocities of the order of 107 m/s. The intracloud discharge had a length of more than 10 km and was oriented primarily vertically. The VHF radiation during the intracloud discharge exhibited the three phases reported in the literature for cloud discharges not associated with ground discharges. The highest level of VHF activity during the flash occurred during 4.3 ms just after a 2.4 ms quiet period following the first return stroke. These VHF sources were located primarily at the top of the return stroke channel.
Optical image and laser slope meter intercomparisons of high‐frequency waves
Authors: Lubard S. C. , Krimmel J. E. , Thebaud L. R. , Evans D. D. , Shemdin O. H.
Published: February 2008

Spectral analyses of optical images of the ocean surface, obtained by the Riverside Research Institute digital video system, are presented and compared with wave data measured simultaneously by the Jet Propulsion Laboratory (JPL) Waverider‐mounted laser slope meter. The image analyses, which incorporate several new ideas, provide two‐dimensional wave number spectra of slope, covering wavelengths from 10 cm to 10 m. These slope spectra are converted to wave height spectra by a new technique which includes the effects of sky radiance gradients. Space‐time spectra are also presented for waves whose frequencies are less than 2 Hz. The JPL slope frequency spectra are compared with image wave number spectra which have been converted to frequency spectra by use of the gravity wave dispersion relation. Results of comparisons between the frequency spectra obtained from the two different measurements show reasonable agreement for frequencies less than 3 Hz.
Analysis of precipitation chemistry at a central Pennsylvania site
Authors: Bowersox Van C. , de Pena Rosa G.
Published: February 2008

As part of the multistate atmospheric power production pollution study precipitation chemistry network, precipitation has been sampled on a storm‐by‐storm basis at a rural central Pennsylvania site operated by Pennsylvania State University since October 1976. These precipitation data have been analyzed for sulfate, nitrate, ammonium, and hydronium ions for the years 1977 and 1978, and both years exhibit the same general behavior with respect to these chemical species: (1) sulfate concentration in precipitation varies with season, with high values in the summer and low values in the winter, (2) sulfate ion is the major determinant of precipitation acidity, though sulfate alone does not account for the total H3O+ concentration, (for snow and other frozen precipitation the relation between sulfate and H3O+ is less pronounced), (3) nitrate ion of concentrations similar to those of sulfate does not correlate well with hydronium ion in liquid precipitation but does correlate with H3O+ in snow and frozen precipitation, and (4) ammonium ion concentrations in precipitation can be explained by assuming an equilibrium state between the cloud water and gas phase ammonia.
The role of deep sea heat storage in the secular response to climatic forcing
Authors: Hoffert Martin I. , Callegari Andrew J. , Hsieh Ching‐Tzong
Published: February 2008

The influence of the world oceans on climatic response is considered here with emphasis on the heat transferred to waters beneath the well‐mixed surface layer and to polar bottom water forming zones. An upwelling‐diffusing model is formulated to treat this problem whose effective transport properties are calibrated from the steady state vertical profiles of radiocarbon, potential temperature and other tracers measured by chemical oceanographers. The key issue with regard to the question of atmospheric temperature response to external climatic forcing is whether heat is exchanged between the surface mixed layer and deep sea at rates comparable to heat transfer rates between the planetary radiation field and the atmosphere‐mixed layer system. An important model parameter appearing in the analysis is the polar sea warming coefficient ∏ equal to the rate of change of polar sea temperature relative to changes in areally averaged mixed layer temperature. For ∏ values in the range of 0 to 2 the models predicts response times in the range of 8 to 20 years to attain 63% of the equilibrium temperature change for a step function climatic forcing, and 50 to 1000 years to get 90% of the equilibrium response. These may be compared with the roughly 4 year response time one gets with an oceanic mixed layer only model. To study the carbon dioxide climate problem, a more realistic time‐dependent forcing function is used based on the historical growth of fossil fuel CO2 and a logarithmic scaling law for the temperature increment which would obtain at any instant if the system were in radiative‐convective equilibrium. Our results suggest the influence of deep sea thermal storage could delay the full value of temperature increment predicted by equilibrium models by 10 to 20 years in 1980 to 2000 A.D. time frame. Also considered is the model response to periodic forcing, the sensitivity of the results, and the implications of the model results with regard to climatic changes on a decadal to millenial timescale.
Coastal flow in the northwest Gulf of Alaska: The Kenai Current
Authors: Schumacher J. D. , Reed R. K.
Published: February 2008

Recent data from the northwest Gulf of Alaska reveal a coastal current which flows westward along the Kenai Peninsula (mainly within 30 km of shore), enters Shelikof Strait, and exits to the southwest of Kodiak Island. This flow, which we call the Kenai Current, has a large seasonal variation in baroclinic transport and maximum surface speed; transport is typically about 0.3×106 m3/s but exceeds 1.0×106 m3/s in fall, with concurrent speed increases from 15–30 cm/s to over 100 cm/s. The coastal flow is clearly distinct from the offshore Alaskan Stream; its seasonal signal is mainly related to a cross‐shelf pressure gradient, which responds to an annual hydrological cycle. Current records from Shelikof Strait substantiate the presence of an annual signal and indicate that wind forcing has maximum effect from December through February, but it does not appear to augment flow at other times.
Nucleation of ammonium chloride in the gas phase and the influence of ions
Authors: Banic C. M. , Iribarne J. V.
Published: February 2008

Homogeneous nucleation Of NH4Cl from NH3 and HCl was studied. When no ions or neutral radicals were present, the nucleation rate increased exponentially with increasing supersaturation above a threshold value. Increasing relative humidity acted so as to reduce the threshold. The curves obtained are consistent with the expression for the free energy of critical embryo formation based on the reaction NH3 + HCl = NH4Cl. Water vapor does not enter into the reaction but acts as a catalyst. When ions and radicals were added to the reactants, the nucleation rates were enhanced, and the thresholds were reduced; negative ions were the most efficient in producing these effects. An inflection was also observed in these cases, and the general shape of the curves log (nucleation rate) versus concentration of reactants changed, indicating a change in the reaction mechanism.
Seasat altimeter observations of dynamic topography in the Gulf Stream Region
Authors: Cheney Robert E. , Marsh James G.
Published: February 2008

Individual Seasat altimeter profiles in the western North Atlantic have been differenced with the best available geoid model to remove the gravitational component. The resulting sea surface height profiles compare remarkably well with independent oceanographic observations. The Gulf Stream is clearly apparent in each profile as a 1‐ to 2‐m step, and known positions of cyclonic and anticyclonic rings correspond with depressions and elevations, respectively, with amplitudes as large as 95 cm. Some of the most important altimeter data for analyzing the dynamic ocean signal were gathered during the last month of the mission when the same ground track was repeated every 3 days. These data allow detailed examination of time‐varying ocean phenomena, since the gravitational component is time‐invariant. One set of collinear passes clearly shows a cyclonic ring as it moves out from underneath the spacecraft's track, an event which was simultaneously observed with the aid of a satellite‐tracked surface buoy. Another striking feature seen in the altimeter data set is the apparent variability exhibited by the Gulf Stream. On time scales of a few days, surface transport indicated by the sea surface height difference across the stream varied by nearly 30%, and over the entire 3‐month period much larger fluctuations were observed, suggesting significant changes in total mass transport. Altimetry may provide an effective means of determining the time and space scales associated with these variations.
Limits on oxygen concentration in the prebiological atmosphere and the rate of abiotic fixation of nitrogen
Authors: Kasting J. F. , Walker James C. G.
Published: February 2008

Two possible scenarios in early terrestrial atmospheric evolution are examined using a one‐dimensional chemistry and flow model of the atmosphere. In each case the production of oxygen results from photolysis of H2O followed by the escape of hydrogen to space. In case 1 the rate of release of reduced volcanic gases is assumed to be greater than the oxygen production rate. This leads to ground‐level oxygen concentrations on the order of 10−13 PAL (present atmospheric level). In case 2 the volcanic reduced gas source is omitted, as might have been the case during an extended period of decreased tectonic activity. The oxygen concentration would then have been limited to ∼4 × 10−8 PAL by reaction with dissolved ferrous iron in the early oceans. The case 1 atmosphere is shown to be reducing, and the case 2 atmosphere oxidizing, based on the relative concentrations of reduced versus oxidized radical species present in the troposphere. Redbeds should have been able to form under case 2 conditions, but not under case 1. The NO produced by lightning discharges is converted primarily to HNO in case 1 and to HNO3 in case 2. In either case, fixed nitrogen was probably sufficiently scarce to be a limiting nutrient for marine organisms.