bluuebunny/crossref_metadata_2025 huggingface dataset:
Ratios of peroxyacetyl nitrate to active nitrogen observed during aircraft flights over the eastern Pacific Oceans and continental United States
Authors: Ridley B. A. , Shetter J. D. , Gandrud B. W. , Salas L. J. , Singh H. B. , Carroll M. A. , Hübler G. , Albritton D. L. , Hastie D. R. , Schiff H. I. , Mackay G. I. , Karechi D. R. , Davis D. D. , Bradshaw J. D. , Rodgers M. O. , Sandholm S. T. , Torres A. L. , Condon E. P. , Gregory G. L. , Beck S. M.
Published: February 2008

During August and September 1986, 11 aircraft flights were made over the eastern Pacific Ocean and continental United States. The suite of observations included simultaneous measurements of peroxyacetyl nitrate (PAN) and active nitrogen (NOx = NO + NO2). At altitudes of 4.5–6.1 km in the middle free troposphere, PAN was usually 5–6 times NOx in maritime air masses and 2–4 times NOx in continental air masses. In air masses of tropical origin, or in the marine boundary layer, both PAN and NOx were typically less than 20–30 parts per trillion by volume, and the PAN to NOx ratio was less than one. The observations show that PAN can be a major component of the odd nitrogen budget in the middle free troposphere and strongly reinforce earlier views that the abundance is mainly governed by long‐range transport processes including formation during transport and continental boundary layer to free tropospheric exchange of PAN and its precursors. Unlike reservoir HNO3, PAN can be transformed to active nitrogen and peroxy radicals by a variety of physical atmospheric processes that lead to air mass warming. Since NOx plays a critical role in determining photochemical O3 production, which in turn determines the oxidative power of the atmosphere, the observed large ratios of reservoir PAN to active NOx imply an important photochemical and dynamical role for PAN in the eastern Pacific remote free troposphere.
Band oscillator strengths of the (2, 1)–(12, 1) Schumann‐Runge bands of O2 from absolute absorption cross‐section measurements at room temperature
Authors: Yoshino K. , Esmond J. R. , Cheung A. S.‐C. , Freeman D. E. , Parkinson W. H.
Published: February 2008

The absolute absorption cross sections of the (2, 1)–(12, 1) Schumann‐Runge bands of O2 at room temperature have been obtained from measurements of the total absolute absorption cross sections arising from transitions from the ground‐state levels with υ″ = 0 and 1 by subtraction of the υ″ = 0 contributions, which have been synthesized from our previous determinations of the band oscillator strengths, line center positions and predissociation line widths of the (υ′, 0) Schumann‐Runge bands of O2. The resultant absolute absorption cross sections of the (2, 1)–(12, 1) bands have been integrated numerically to obtain the band oscillator strengths. Our experimental band oscillator strengths are somewhat lower than the experimental values of Lewis et al.(1986) but are in good agreement with the recently calculated values of Friedman (1990).
Error estimates of background atmospheric CO2patterns from weekly flask samples
Authors: Tans Pieter P. , Thoning Kirk W. , Elliott William P. , Conway Thomas J.
Published: February 2008

The precision and accuracy of trends and seasonal cycles of CO2, as determined from grab samples, was investigated. First, the statistical aspects of infrequent (weekly) sampling were studied by simulating, via a partially random procedure, parallel time series of CO2flask samples. These simulated flask series were compared to the continuous analyzer records from which they had been derived. The second approach to studying the uncertainties of flask records was to compare real flask results with simultaneous hourly mean concentrations of the in situ analyzers at the Geophysical Monitoring for Climatic Change observatories at Point Barrow, Mauna Loa, Samoa, and the south pole. The latter comparisons emphasized experimental, rather than statistical, errors. The uncertainties and sampling biases depend on the site and on the period of averaging. For monthly means the uncertainty varies from 0.2 to 0.6 ppm (one standard deviation, parts per million by volume), being largest for Barrow. Sampling biases for monthly means at Barrow and Mauna Loa are significant, up to 0.5 ppm. Experimental errors are the dominant error source for annual averages, and spurious interannual variations can be up to 0.4 ppm.
Interactions between the sulfur and reduced nitrogen cycles over the central Pacific Ocean
Authors: Quinn Patricia K. , Bates Timothy S. , Johnson James E. , Covert David S. , Charlson Robert J.
Published: February 2008

In April and May of 1988 along 170°W from 53°N to 14°S, simultaneous concentration measurements were made of the major components of the sulfur and reduced nitrogen cycles. The species measured included sea water dimethylsulfide, DMS (s), and total ammonia, NH3 (s,tot) = NH3 (s) + NH4+ (s); atmospheric gas phase DMS (g), NH3 (g), and SO2 (g); and atmospheric particulate phase NH4+ (p), non‐seasalt sulfate, nss SO4= (p), and methanesulfonate, MSA (p). Based on isentropic calculated back trajectories at 1000, 950, 850, and 700 mbar arrival heights, three apparent air mass regimes were encountered; one from 50°N to 30°N which recently had been in contact with Asia, one from 29°N to 15°N which had passed over Hawaii during a volcanic eruption several days earlier, and one from 14°N to 11°S which was the most representative of remote marine air. Changes in the relative concentrations of the atmospheric S and NH3 species reflected the origin of the air masses sampled. The NH3 (g) concentrations were low over the entire region studied, indicating that the lifetime of NH3 in the marine boundary layer is on the order of hours. These low NH3 concentrations led to only partially neutralized sulfate aerosol particles. The mean NH4+ (p) to nss SO4= (p) molar ratio was 1.3±0.71. The highest ratios were found in continentally influenced air masses where the NH4+ (p) was most likely of continental origin and in remote marine air masses with an absence of continentally derived nss SO4= (p). The lowest ratios found were a result of high nss SO4= (p) concentrations in air masses influenced by the Hawaiian volcanic plume. Seawater concentrations of DMS (s) and NH3 (s,tot) were lowest in the North Pacific central gyre and highest in the northern latitudes and near and south of the equator.
A photochemical model of ozone interference effects in laser detection of tropospheric OH
Authors: Smith Gregory P. , Crosley David R.
Published: February 2008

Laser‐generated interference in the laser‐induced fluorescence detection of tropospheric hydroxyl is addressed by a detailed photochemical model. This phenomenon arises through photolysis of ozone by the detection laser and subsequent reaction of O(1D) with H2O to form OH. The approach is direct time integration of the coupled differential equations describing the pertinent chemical reactions, collisional energy transfer, and photolytic and spectroscopic processes, including an assessment of limitations due to uncertainties in the input parameters. The goal is to use the model to quantitatively design OH detection methods so that the experimental results need not rely on such a model for interpretation. Previously reported measurements of tropospheric OH appear to have been contaminated by ozone interference effects and by optical saturation of the monitoring transition. However, suggested improvements can reduce the problem to interference levels below 2×105 OH molecules/cm3, permitting measurements useful for testing theories of fast tropospheric photochemistry.
Uncertainties in total ozone amounts inferred from zenith sky observations: Implications for ozone trend analyses
Authors: Stamnes Knut , Pegau Scott , Frederick John
Published: February 2008

In an effort to determine ozone measurement uncertainties associated with zenith sky radiation observations, a preliminary study involving radiative transfer calculations has been conducted to simulate ozone inference from Dobson spectrophotometer observations. By using a comprehensive radiative transfer algorithm, a model atmosphere, and a suitable set of ozone absorption cross sections, we have simulated, for a specific ozone profile and an ozone amount of about 350 Dobson units, the effects of cloud optical depth, cloud altitude, vertical distribution of ozone, temperature profile, and surface albedo on the total amount of ozone inferred by the Dobson procedure from zenith sky observations. Our simulations indicate that significant uncertainties may arise in determining ozone amounts from measurements of zenith sky intensity. The implications of these uncertainties for ozone trend analyses are described, showing, for example, that an appreciable error could arise in deduced ozone trend should tropospheric ozone double in the foreseeable future but not be taken into account in total ozone data processing. The radiative transfer algorithm may, furthermore, be employed to construct charts for use at each Dobson instrument site in processing zenith sky ozone observations. Such charts are currently derived empirically by comparing direct Sun and zenith sky observations. The theoretically derived charts would, however, need on‐site correcting to account for instrumental effects. Construction and use of synthetic correction tables for any particular station may alleviate difficulties encountered in the creation of empirical correction tables, since it avoids problems related to (1) time lapse between measurements and (2) diffuse radiation from forward scattering in clouds influencing the direct Sun measurements.
Atmospheric emissions and trends of nitrous oxide deduced from 10 years of ALE–GAGE data
Authors: Prinn R. , Cunnold D. , Rasmussen R. , Simmonds P. , Alyea F. , Crawford A. , Fraser P. , Rosen R.
Published: February 2008

We present and interpret long‐term measurements of the chemically and radiatively important trace gas nitrous oxide (N2O) obtained during the Atmospheric Lifetime Experiment (ALE) and its successor the Global Atmospheric Gases Experiment (GAGE). The ALE/GAGE data for N2O comprise over 110,000 individual calibrated real‐time air analyses carried out over a 10‐year (July 1978–June 1988) time period. These measurements indicate that the average concentration in the northern hemisphere is persistently 0.75±0.16 ppbv higher than in the southern hemisphere and that the global average linear trend in N2O lies in the range from 0.25 to 0.31% yr−1, with the latter result contingent on certain assumptions about the long‐term stability of the calibration gases used in the experiment. Interpretation of the data, using inverse theory and a 9‐box (grid) model of the global atmosphere, indicates that the N2O surface emissions into the 90°N–30°N, 30°N–0°, 0°–30°S, and 30°S–90°S semihemispheres account for about 22–34, 32–39, 20–29 and 11–15% of the global total emissions, respectively. The measured trends and latitudinal distributions are consistent with the hypothesis that stratospheric photodissociation is the major atmospheric sink for N2O, but they do not support the hypothesis that the temporal N2O increase is caused solely by increases in anthropogenic N2O emissions associated with fossil fuel combustion. Instead, the cause for the N2O trend appears to be a combination of a growing tropical source (probably resulting from tropical land disturbance) and a growing northern mid‐latitude source (probably resulting from a combination of fertilizer use and fossil fuel combustion). The exact combination of these sources which best fits the data depends on the assumed tropospheric‐stratospheric exchange rates for N2O in the northern hemisphere relative to the southern hemisphere. Accepting a theoretically‐calculated N2O lifetime of 166±16 years due to stratospheric destruction only, we deduce from the ALE/GAGE data a 10‐year average global N2O emission rate of (20.5±2.4) × 1012 g N2O yr−1, but with significant year‐to‐year variations in emissions associated perhaps with year‐to‐year variations in tropical land disturbance.
N2O production mechanism from the interaction of discharge‐excited species
Authors: Fraser Mark E. , Tucker Thomas R. , Piper Lawrence G. , Rawlins Wilson T.
Published: February 2008

We have examined the interaction of discharge effluents to understand the formation mechanism of N2O in the upper atmosphere and in published studies employing discharge‐flow systems. N2O production rates were determined under various discharge‐flow conditions and are consistent only with a process in which both N2 and O2 species are excited and are present in large relative concentrations. We postulate N2(v ≥ 15) + O2(a1Δ or b1Σ) as the responsible mechanism.
Tropospheric OH and the lifetimes of hydrochlorofluorocarbons
Authors: Prather Michael , Spivakovsky Clarisa M.
Published: February 2008

Hydrochlorofluorocarbons (HCFCs) may be used as alternatives for the chlorofluorocarbons (CFCs). Lifetimes for the HCFCs are predicted here in two ways: integrating their loss with a global model, and scaling to another compound with a better known lifetime. Both approaches are shown here to yield similar results. Three‐dimensional fields of modeled tropospheric OH concentrations are used to calculate lifetimes against destruction by OH for the HCFCs and other hydrogenated halocarbons. The OH fields are taken from a three‐dimensional chemical transport model [Spivakovsky et al., 1990a] that accurately simulates the global measurements of methyl chloroform (derived lifetime of 5.5 yr). The lifetimes of various hydro‐halocarbons are shown to be insensitive to possible spatial variations and seasonal cycles. It is possible to scale the HCFC lifetimes to that of methyl chloroform or methane by using a ratio of the rate coefficients for reaction with OH at an appropriate temperature, about 277 K.
Arctic boundary layer ozone variations associated with nitrate, bromine, and meteorology: A case study
Authors: Li Shao‐Meng , Winchester John W. , Kahl Jonathan D. , Oltmans Samuel J. , Schnell Russell C. , Sheridan Patrick J.
Published: February 2008

Gas and aerosol measurements at Barrow, Alaska during the spring of 1986 confirm the inverse relationship between particulate excess bromine (xBr) and O3. In addition to this inverse XBr‐O3 relationship, several other factors were found to be important in understanding the springtime variability of O3 at Barrow. They are (1) O3 concentration variability associated with NOx chemistry at high pollutant levels or transport of primary pollutant O3 from lower latitudes, (2) displacement of air masses of high O3 content with air masses low in O3 but high in sea salt, suggesting potential roles of sea salt in O3 fluctuations, and (3) when pollutant levels were low, advection of air that can cause gradual change in O3 with more rapid inversely related fluctuations of O3 and xBr superimposed. Under the conditions of factor 3 the trend and anticorrelation each accounted for about one quarter of the variance in O3, suggesting a role for other compounds or low level reactive nitrogen species and gas‐particle interaction in the photolytic O3 destruction process.
Milankovitch cycles in Neocene deep‐sea sediment
Authors: Dean Walter E. , Gardner James V.
Published: February 2008

Pelagic carbonate sediments from the world ocean basins commonly show cyclic variations in amount and/or degree of preservation of biogenic calcite, with periodicities of several tens to several hundreds of thousands of years. The direct causes of these cycles are fluctuations in noncarbonate dilution, carbonate production, carbonate dissolution, and/or current winnowing. The overall driving force, however, is variation in the earth's orbital characteristics (Milankovitch cycles) through their influence on global climate and depositional processes. The main inferred climatic effects of orbital perturbations are on global ice volume, global temperature, ocean circulation, and distribution of climatic patterns. Eustatic sea level is directly related to ice volume, as is the rate of erosion of clastic material from continental margins. Changes in volume of sea ice affect the volume and intensity of bottom water flow, which in turn may cause changes in the intensity of sediment winnowing by bottom currents, in the intensity of upwelling of nutrient‐rich bottom waters, and in the depth of carbonate dissolution. Change in productivity of calcareous plankton are difficult to prove as a cause of carbonate cycles but may have contributed to the formation of carbonate cycles off northwest and southwest Africa. Fluctuations in winnowing of fine‐grained components have been demonstrated as a cause of cyclic variations in the coarse‐fraction component of carbonate sediments in the southwest Pacific. Dilution of carbonate by clastic material probably was a major cause of fluctuations in carbonate content of deep‐sea sediments off northwest and southwest Africa. Carbonate dissolution cycles probably are the most common manifestation of fluctuations in bottom water flow. Dissolution cycles are common in Quaternary and Neogene sediments of the North Atlantic, Caribbean, and eastern equatorial Pacific. The main cause of the carbonate dissolution was shoaling of the carbonate compensation depth during the early Neogene in response to climatically induced fluctuations in the thickness of Antarctic Bottom Water.
Carbonate mineral cycles in ramp slope sediment: Eastern Gulf of Mexico
Authors: Gardulski Anne F. , Mullins Henry T. , Oldfield Bronya , Applegate Joe , Wise Sherwood W.
Published: February 2008

Carbonate mineral cycles, controlled by Pleistocene climatic rhythms, have been discovered in a 11.6 m‐long‐piston core from the west Florida carbonate ramp slope at 890 m of water depth in the eastern Gulf of Mexico. Relatively high concentrations of aragonite, magnesian calcite, and dolomite, as well as insoluble residues, total organics, and mud‐sized sediment, all correlate with glacial periods defined by oxygen isotope stratigraphy. The aragonite is a low‐strontium variety derived from pteropods, and there is no evidence that concentration variations are controlled by dissolution. We propose that these mineral and textural cycles are the product of a combination of increased biological productivity and dilution by fine‐grained terrigenous mud during glacial episodes. Aragonite cycles in Bahamian periplatform slope sediment have also been correlated with climatic change. There the aragonite is a high‐strontium variety derived from shallow‐water calcareous algae, with relatively high concentrations correlated with high sea levels during interglacial periods. The carbonate mineral cycles along the west Florida ramp slope are 180° out of phase with Bahamian examples and also lack their marked asymmetry. It is now apparent that for deepwater, continental margin carbonates there are two types of carbonate mineral cyclicity: one that is “pelagic driven” during glacial periods, and one that is “platform driven” during interglacials. These contrasts emphasize the differences in deep water cyclic sedimentation on carbonate ramps versus rimmed carbonate platforms that are controlled by physiography, sediment source, oceanographic setting and proximity to terrigenous input. The productivity‐dilution model proposed here may be a valuable modern analog for ancient carbonate sequences deposited in epicontinental seas or on ramps attached to continental margins.
Episodic nature of the Cenozoic marine record
Authors: Rampino Michael R. , Stothers Richard B.
Published: February 2008

Various suggestions of a geological periodicity of 2–7 m.y. have been made in the literature. If such periods exist, they fall between the earth' orbital (Milankovitch) periods and the solar system's galactic (Oort) periods and have no known internal or external source. To study the period range 1–10 m.y., four types of Cenozoic marine data were subjected to formal time series analysis. No significant periodicities were found, and only a mean interval between global marine episodes (∼5 ± 2 m.y.) could be defined. Possible causes of the variability are discussed.
Evolutionary changes in some Late Neogene planktonic foraminiferal lineages and their relationships to paleoceanographic changes
Authors: Malmgren Björn A. , Berggren W. A.
Published: February 2008

The timing of evolutionary changes in some late Neogene lineages of planktonic foraminifers and major paleoceanographic events are evaluated to assess possible correspondences between paleoclimatic change (in a broad sense) and evolutionary innovations. Previously published data on evolutionary changes in theGloborotalia inflatalineage, theGloborotalia tumidalineage, and theGloborotalia truncatulinoideslineage, and new data on theSphaeroidinella dehiscenslineage, are used in the study. Most evolutionary rate changes in these lineages are shown to occur near times of major paleoceanographic events. For example, rapid increase in conicality and weakening of the keel in theG. inflatalineage in the latest Miocene coincided with the 6.2‐Ma event (global cooling, sea level regression, and shift in carbon isotope ratios in foraminiferal tests). Disappearance of keeled morphotypes (Globorotalia conomiozea) in the same lineage, and appearance of nonkeeled forms with rounded periphery (Globorotalia puncticulata) coincided with the return of warmer, more stable climatic conditions, and transgressions at the Miocene/Pliocene boundary (5.3 Ma). Phyletic transformation fromGloborotalia plesiotumidaintoG. tumidaalso took place across this boundary, and supplementary apertures first developed in theS. dehiscenslineage. Supplementary apertures in theS. dehiscenslineage were rare through the early Pliocene but became rapidly dominant in the populations in the interval between 3.4 and 3.3 Ma, where major paleoceanographic changes occurred (the 3.4‐to 3.2‐Ma event marked by cooling of surface waters and increased production of bottom waters at high latitudes, resulting in strengthening of ocean vertical and horizontal gradients). Forms without a supplementary aperture became extinct only 0.3–0.4 m.y. later (3.0 Ma), and at about the same time, G.inflataappeared in the fossil record. Although evolutionary change exhibits striking temporal correlation with climatic change, some evolutionary time series do not show any obvious relationship to paleoclimate: chamber number in the final whorl in theG. inflatalineage and conicality inG. truncatulinoides.
Changes in redox conditions in deep‐sea sediments of the subarctic North Pacific Ocean: Possible evidence for the presence of North Pacific Deep Water
Authors: Dean Walter E. , Gardner James V. , Hemphill‐Haley Eileen
Published: February 2008

Cores of upper Quaternary and Holocene sediment from the subarctic North Pacific north of about 48°N contain one or more layers of oxidized brown sediment interbedded within predominantly reduced green sediment. The brown layers are enriched in several trace elements, especially Mn, Mo, Ni, and Co, relative to the green layers. Where multiple oxidized layers are present, the intensity of the brown coloration and the magnitude of trace element enrichment often decrease with depth, suggesting that the oxidized layers are unstable and are being chemically reduced at depth. The oxidized layers represent a change in redox conditions between the North Pacific red clay province and the subarctic biosiliceous green clay province. The redox change may have been caused by an increase in supply of dissolved oxygen to bottom waters during glacial‐interglacial transitions as the result of the periodic formation of a seasonal bottom water mass in the northeastern Pacific Ocean.
Reconstructing the ocean carbon system variation during the last 150,000 years according to the Antarctic nutrient hypothesis
Authors: Keir Robin S.
Published: February 2008

In this study, the Vostok ice core CO2 record and the δ13C difference between the deep Atlantic and Pacific (δa − δp) are used in combination with model simulations to analyze the history of the ocean carbon pump and the sources of Atlantic deep water during the last 150 kyr. It is assumed that the mechanism by which the glacial atmospheric CO2 decreased is an increase in the ratio of Antarctic net carbon production to upwelling in that region. Results from a wide range of circulations and Antarctic net carbon productions input into a 14‐box ocean‐atmosphere model show that similar distributions of phosphate, δ13C, atmospheric CO2 content and surface versus deep radiocarbon age are produced once the following parameters are fixed: (1) the ratio of net carbon production to upwelling in the Antarctic region, (2) the ratio of Northern Component Water to Antarctic Bottom Water input into the Atlantic, and (3) the total upwelling into the low‐latitude surface waters. Therefore rather arbitrary circulations and Antarctic net production values can be used to map model simulated geochemical properties as a function of these parameters. Decrease in atmospheric CO2 and Atlantic to Pacific δ13C difference are calculated from the model for constant low‐latitude upwelling, and these are mapped as a function of the ratios 1 and 2 above. The isolines of these two geochemical properties tend to be orthogonal, and one can position any ΔpCO2, δa − δp pair on an overlay of the two maps. This is done for coeval ice core CO2 and marine sedimentary δ13C data for the last 150 kyr. One finds that the history of the Antarctic carbon pump efficiency varies with the same pattern as that of the atmospheric CO2. The fraction of Northern Component Water entering the Atlantic tends to vary with the same shape function as the global marine δ18O curve.
The Southern Oscillation recorded in the δ18O of corals from Tarawa Atoll
Authors: Cole Julia E. , Fairbanks Richard G.
Published: February 2008

In the western equatorial Pacific, the El Niño/Southern Oscillation (ENSO) phenomenon is characterized by precipitation variability associated with the migration of the Indonesian low pressure cell to the region of the date line and the equator. During ENSO events, Tarawa Atoll (1°N, 172°E) experiences heavy rainfall which has an estimated δ18O of about −8 to −10‰ δ18OSMOW. At Tarawa, sufficient precipitation of this composition falls during ENSO events to alter the δ18O and the salinity of the surface waters. Oxygen isotope records from two corals collected off the reef crest of Tarawa reflect rainfall variations associated with both weak and strong ENSO conditions, with approximately monthly resolution. Coral skeletal δ18O variations due to small sea surface temperature (SST) changes are secondary. These records demonstrate the remarkable ability of this technique to reconstruct variations in the position of the Indonesian Low from coral δ18O records in the western equatorial Pacific, a region which has few paleoclimatic records. The coral isotopic data correctly resolve the relative magnitudes of recent variations in the Southern Oscillation Index. Combining the Tarawa record with an oxygen isotopic history from a Galápagos Islands coral demonstrates the ability to distinguish the meteorologic (precipitation) and oceanographic (SST) anomalies that characterize ENSO events across the Pacific Basin over the period of common record (1960–1979). Comparison of the intensity of climatic anomalies at these two sites yields insight into the spatial variability of ENSO events. Isotope records from older corals can provide high‐resolution, Pacific‐wide reconstructions of ENSO behavior during periods of different climate boundary conditions.
Revision of United States standard atmosphere 90 to 700 kilometers
Authors: Champion Kenneth S. W. , Minzner Raymond A.
Published: February 2008

A 1962 revision of the United States standard atmosphere was recently announced. The high‐altitude part of the previous standard was based upon a small number of relatively inaccurate pressure and density data available in 1955. High‐altitude atmospheric data obtained with IGY rockets and satellites demonstrated the inadequacies of the standard and provided the basis for a major revision above 20‐km altitude. The large amount of satellite‐drag density data and rocket‐derived pressure data required the use of model‐generation processes involving both pressure‐temperature altitude relationships and density‐temperature altitude relationships. A high‐altitude model (90–700 km) was developed by using the process of linearly segmented temperature functions, starting from reference values and working upward, matching observed pressure‐altitude and density‐altitude profiles. This technique of model generation permitted continuity with an independently developed low‐altitude model (20–90 km). The imposed requirement that the high‐altitude part of the new standard be defined in terms of molecular‐scale temperature functions that are linear with respect to geometric, rather than geopotential, altitude, introduced considerable complexity to the defining equations. With molecular‐scale temperature as the principal defining property, it was necessary to establish a molecular‐weight function as a secondary defining property in order to compute kinetic temperatures and other atmospheric properties not directly related to molecular‐scale temperature. The assumption that diffusive equilibrium dominates the atmosphere above 120‐km altitude, coupled with numerous assumptions concerning photodissociation and recombination rates of known atmospheric molecules, served as the basis for the computation of number density of the various species and, hence, mean molecular weight as a function of altitude. The definitions of this revised atmospheric model were adopted by the Committee on Extension to the United States standard atmosphere on March 15, 1962, and thereby this model became the basis for the 90‐ to 700‐km region of the revised United States standard atmosphere.
Atmospheric tides and associated magnetic effects
Authors: Fejer J. A.
Published: February 2008

The dynamical theory of atmospheric tides and its relation to observations on the ground and in the upper atmosphere are reviewed briefly. The lunar tidal oscillations of atmospheric pressure observed on the ground are thought to be almost entirely due to gravitational forces, whereas the solar tidal oscillations are believed to be mainly caused by solar heating. Previous theories of resonant, gravitational excitation of the solar tidal oscillations are not consistent with models of the upper atmosphere obtained from rocket measurements. Tidal oscillations at ionospheric heights are inadequately known experimentally and are inadequately explained by present theories, which neglect viscous losses and the ionized nature of the upper atmosphere and whose linear approximations break down at ionospheric height. The dynamo theory attributes the quiet‐day variations of the geomagnetic field to tidal oscillations at ionospheric height. The theory has been used either to derive the magnetic variations from an assumed tidal wind system or to derive the tidal wind system from the observed magnetic variations. The results of both types of calculations lend broad support to the dynamo theory, although neither approach is free of arbitrary assumptions. The additional daily magnetic variations observed during magnetically disturbed days are particularly intense in the auroral zone. These variations are believed to be caused by some form of interaction of the solar wind with the geomagnetic field, but the nature of the interaction is not yet known with certainty. Various proposed theories of these daily disturbance variations are described, and one is discussed in detail. This theory predicts that the generating mechanism responsible for the daily disturbance variations is present, in reduced strength, even on magnetically quiet days. Observations tend to confirm this conclusion.
Physical processes in the D region of the ionosphere
Authors: Reid George C.
Published: February 2008

This paper summarizes our present knowledge of the physical processes likely to be of major importance in determining the characteristics of the D region of the ionosphere. The basic processes are divided into three categories: (1) primary ionizing mechanisms; (2) interactions involving free electrons, ions, and the neutral gas; (3) mechanical and electrodynamic mechanisms that lead to redistribution of ionization. The information currently available in each of these categories is discussed, and major gaps in our knowledge are indicated.
Application of the theory of eigenfunctions to the calculations of surface wave velocities
Authors: Keilis‐Borok V. I. , Neigauz M. G. , Shkadinskaya G. V.
Published: February 2008

Surface wave phase velocities for an inhomogeneous medium are usually given as eigenvalues of the wave equation. This is a differential equation (Love waves) or pair of differential equations (Rayleigh waves) of the second order. By means of a change of variable the problem is reducible to finding the zeros of a first‐order differential equation or pair of differential equations of first order. The solution can be obtained in any order of surface waves, and the eigenfunctions can be obtained as well by means of this transformation. The solution is thus amenable to computation.
A model for planetary igneous differentiation
Authors: McConnell Robert K. , McClaine Leslie A. , Lee D. William , Aronson James R. , Allen Ronald V.
Published: February 2008

Numerical models for igneous activity on any planet must be based on thermal properties and melting relationships for realistic multicomponent systems. A consistent model for the composition of the earth's mantle may be obtained by considering a mixture of basalt and dunite, as postulated by Ringwood and others, if the uranium, thorium, and potassium concentrations of the basalt are similar to that of basalts dredged from the deep ocean floors. Present evidence does not indicate that the bulk composition of the moon is appreciably different from that of the earth's mantle.

On the basis of a review of existing phase equilibria and high pressure studies, we predict melting behavior as a function of pressure and temperature for a composition equivalent to 1 part basalt and 3 parts dunite. The specific heat and fusion properties of the important minerals in this system are reviewed. The implications of these data for an understanding of magma generation are discussed.

A review of the factors influencing the thermal conductivity of rocks indicates that when considering the details of heat conduction under conditions likely to be encountered within the earth's upper mantle and the moon, a model invoking constant phonon conductivity and temperature independent photon mean free path may be unrealistic. A more likely, but still oversimplified, model has a phonon conductivity inversely proportional to temperature, and, unless scattering dominates, a photon mean free path directly proportional to temperature over the range of interest. Pressure should not significantly affect the thermal conductivity within the upper mantle, except by changing the stable mineral assemblage.

When the more important aspects of the melting relationships and thermal properties of the model composition are selected and used to extend thermal history calculations of the moon to include the effects of differentiation through igneous activity, the calculations indicate that a brief period of intense volcanic activity is likely to have occurred at a time which is primarily a function of the moon's temperature at the time of its formation and the concentration of radioactive heat sources. If the temperature of the moon at the time of its formation were 0°C and the uranium content were 0.05 ppm, with Th/U and K/U in the ratio 3.7 and 104, respectively, melting would have begun about 1.5 × 109 years after formation, the intensity being largely controlled by the thermal conductivity. At lower U, Th, and K contents, the onset of volcanism would have been delayed or suppressed completely, depending on the conductivity. Properly selected samples of the moon's surface rocks should thus make it possible to determine its initial temperature. The total thickness of extrusive and intrusive igneous rocks is shown to be critically dependent on the efficiency of radiative heat transfer in removing heat from the interior.
International Symposium on the Physics of the Magnetosphere
Authors: Williams Donald J. , Mead Gilbert D.
Published: February 2008

This volume contains all of the fifteen invited review papers presented at the International Symposium on the Physics of the Magnetosphere, held in the U. S. Department of State, Washington, D. C., September 3–13, 1968. The contributed papers presented at the Symposium are not included; they are appearing in other appropriate journals. By arrangement with the Inter‐Union Commission on Solar‐Terrestrial Physics (IUCSTP), the Symposium was sponsored by the Committee on Space Research (COSPAR), the International Association of Geomagnetism and Aeronomy of the International Union of Geodesy and Geophysics (IUGG‐IAGA), the International Scientific Radio Union (URSI), the International Union of Pure and Applied Physics (IUPAP), and the International Astronomical Union (IAU). It was held by the U. S. National Academy of Sciences and the NASA Goddard Space Flight Center. The Symposium was attended by 325 scientists representing 18 different countries.
An experimental evaluation of single domain theories
Authors: Dunlop David J. , West Gordon F.
Published: February 2008

The Néel theory of magnetization relaxation has been systematically and quantitatively tested for six samples containing synthetic and natural single domain grains. The results of a wide range of experiments involving time, temperature, and direct and alternating magnetic fields were compared with theoretical results predicted by using the Néel theory and the experimental grain size‐coercivity distribution of each sample. Good agreement was found for many experiments involving small field remanences, where grain interaction effects are negligible. Most of the discordant results could be explained by using either the Preisach theory or an extended form of the Néel theory, which takes account of interactions. The two methods are shown to be equivalent, but the Néel theory is more useful in analyzing thermal processes that are intractable by the Preisach method. The similarity of the behavior of synthetic and natural samples suggests that monodomain material is important in many rocks, but experiments on a wide variety of rock types are needed for verification.
The terrestrial influx of small meteoric particles
Authors: Soberman Robert K.
Published: February 2008

The available data on the terrestrial influx of small meteoric particles (mass < 1 gram) are surveyed. Whereas, in the past, flux determinations differed by factors of as much as 100 million, it is shown that recent experimental data are far more consistent, variations being limited to a factor of 10 for particles of mass greater than 10−10 gram. The sensors from which the data are obtained are discussed, with particular emphasis on those used in situ, and inherent uncertainties in the results are pointed out. A best estimate of the cumulative mass distribution influx is given on the basis of the most recent data available. This estimate uses the NASA Meteoroid Environment Model, 1969. Uncertainty limits due to differing experimental results and interpretations are placed upon this flux model. For masses larger than about 10−10 gram, the uncertainty is less than 1 order of magnitude; whereas for smaller particles the uncertainty may still be as large as 4 or 5 orders of magnitude. The present best estimate of the mean density of the small meteoric particles is 0.5 g/cm³, but there are indications that several classes of meteoroids exist with densities ranging from 0.3 to 1.2 g/cm³.
Structure of the magnetopause
Authors: Willis D. M.
Published: February 2008

This paper reviews present understanding of the internal structure of the thin boundary layer, termed the magnetopause, that separates the distorted geomagnetic field in the magnetosphere from the flow of solar plasma in the magnetosheath. The fundamental theoretical concepts of the subject are introduced by considering the structure of the boundary layer that exists when a cold, unmagnetized stream of ions and electrons impinges normally on a vacuum magnetic field. This idealized model indicates how the earth's magnetic field is confined by the impact pressure of the solar wind, the geomagnetic field being terminated by induced shielding currents flowing in the magnetopause. The various idealizations and approximations in this model, such as the assumption of a cold solar plasma and the neglect of the interplanetary magnetic field, are examined critically. The presence of thermal plasma in the magnetosphere modifies the structure of the boundary layer so that the ions penetrate substantially deeper (∼100 km) than the electrons into the geomagnetic field. Complications then arise if the solar plasma has a component of velocity parallel to the confined field, as occurs in the downstream magnetopause that bounds the geomagnetic tail. This additional component of velocity generates electric currents parallel to the magnetic field that may destroy the small‐scale equilibrium of the magnetopause and result in a tangential drag on the geomagnetic cavity. The available experimental information on the magnetopause structure is summarized and related to the theoretical investigations. Although the observations confirm some of the theoretical predictions, much of the detailed theory remains speculative at the present time.
polar magnetic substorms
Authors: Rostoker Gordon
Published: February 2008

The mechanisms by which substorms are generated are still a subject of considerable controversy. A brief review of the historical development of some of the concepts of substorm generation, and the relative merits of these concepts, are discussed against the background of the large number of observational data now available. Polar magnetic substorms are generated through the intensification of the ionospheric current in a localized region of the westward electrojet. At this time field‐aligned currents flow, linking the ionospheric electrojet and magnetospheric current systems near the inner edge of the plasma sheet. It is now apparent that the north‐south component of the interplanetary magnetic field regulates the flow of energy from the interplanetary medium into the magnetosphere. The magnetotail acts as a temporary storage reservoir for this energy, which is eventually released in substorms. Convection is the physical mechanism that dominates in the distribution of energy in the nightside magnetosphere. The over‐all picture presented suggests that substorms are a drastic mechanism by which energy stored in the nightside magnetosphere is dissipated.
Electric fields and plasma convection in the plasmasphere
Authors: Mozer F. S.
Published: February 2008

A review is given of present theoretical and experimental information on quasi‐static electric fields in and near the plasmasphere with the aim of discussing plasma flow within the plasmasphere, dynamo electric fields, and the penetration of electric fields of magnetospheric origin to low latitudes. Data are presented that suggest that the mean temporal variation of electric fields at all latitudes is diurnal, that dynamo electric fields are more important near L = 3 and are less important near and beyond L = 4 than are fields of magnetospheric origin, and that magnetospheric fields with periods that are a reasonable fraction of one day efficiently penetrate the plasmapause.
Petrologic and geophysical significance of mantle xenoliths in basalts
Authors: MacGregor Ian D.
Published: February 2008

Data on the nature of the earth's upper mantle are derived from a combination of direct and indirect techniques. Indirect techniques, which include investigations of the seismic, thermal, electrical, and magnetic structures, monitor bulk properties of extensive regions of the upper mantle. The indirect measurements lead to estimates of the vertical and lateral structures in terms of the acoustic velocities, density, and thermal and electrical properties of the mantle. In contrast, certain geologic processes bring mantle samples directly to the surface. At these locations mantle rocks can be examined in fine detail and serve as a storehouse of descriptive data to calibrate the estimates of lateral and vertical structures given by the indirect geophysical methods. Geologic examples where mantle rocks have been brought through the crust to the surface include two major types of occurrences. The first group consists of large massifs of mafic and ultramafic rocks such as the ophiolites, alpine peridotites, and high‐temperature peridotites. They are brought to the surface by diapiric uprise of mantle material or tectonic forces resulting in the faulting or thrusting of mantle material into crustal environments. The second group includes inclusions of mantle material transported to the surface by host magmas that have their origin in the mantle. The alkalic magmas such as alkaline‐olivine basalts, mugiarites, nephelinites, and kimberlites are most commonly the host magmas. The mantle inclusions are predominantly accidental and represent direct samples torn from the walls of the conduits channeling the magma to the surface. In this sense they represent reverse churn drill holes into the mantle and offer the most direct technique for getting a single profile at a single locality. This report focuses on the progress made in studies concerned with mantle inclusions, particularly insofar as they contribute to knowledge of the physical structure of the mantle.
Paleomagnetic records of polarity transitions, excursions, and secular variation
Authors: Cox Allan , Hillhouse Jack , Fuller Michael
Published: February 2008

In this report we review the past few years research on polarity transitions, short polarity events, excursions of the field, and secular variation. The common element linking these phenomena is that they occur very quickly, so quickly in fact that it is difficult to find rocks which have recorded them completely enough and accurately enough to provide useful magnetic records. Yet an increasing number of paleomagnetists have undertaken research on young rocks, especially on sediments, in the hope of learning more about the fine structure of the earth's field. In part the motivation for this research has been to identify and date unusual swings of the field so that these can be used for purposes of detailed stratigraphic correlation.
Precipitation research
Authors: Peck Eugene L.
Published: February 2008

Major flood events during the past 4 yr in the United States have focused attention on the need for additional research relating to the measurement and estimation of areal distribution of precipitation. The characteristics of the precipitation associated with the storms that produced the major floods varied widely. Major flooding occurred over a large area of the lower Mississippi River Basin from the series of storms which produced a very wet spring in 1973. Unprecedented flooding occurred in northeastern United States following the movement of hurricane Agnes into the area in June 1972 [De Angelis and Hodge, 1972]. A very localized storm near Rapid City, South Dakota, produced approximately 370 mm of rain in 3 hours in June 1972, resulting in devastating flash flooding.
Erosion and sedimentation
Authors: Nordin Carl F.
Published: February 2008

Several significant trends in research on erosion and sedimentation have emerged during the past few years. Physical models, though still important tools for the hydraulician, are giving way to mathematical models. Greater emphasis is being placed on environmental concerns, and interdisciplinary and multidisciplinary research have brought fresh perspectives to some very old problems. Estuaries, coasts, and near‐shore regions finally are receiving the attention commensurate with their importance as great natural resources. The roles of sediments as pollutants and as conveyors and sinks of persistent pollutants; such as pesticides, herbicides, and trace metals have been identified, and a highly specialized science of the interrelation of sediments and water quality is developing.