bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling the February 1990 polar stratospheric cloud event and its potential impact on the northern hemisphere ozone content
Authors: Lefèvre F. , Riishojgaard L. P. , Cariolle D. , Simon P.
Published: February 2008

Balloon‐borne and ground‐based instruments indicated in early February 1990 that a major type II polar stratospheric cloud event occurred above Scandinavia at temperatures as low as −90°C at 30 hPa. We first report in this paper the TOVS/HIRS2 measurements during this period, which show that the polar stratospheric cloud had an area at least equivalent to similar events observed from this instrument during the formation of the Antarctic ozone hole. Then, in order to assess the amount of air chemically processed by this type II PSC, short integrations have been carried out at high resolution (1.5°) with the “Emeraude” GCM, initialized from the ECMWF analysis of February 4, 1990. The temperature and PSC forecasts are described and compared with the analysis and satellite observations, hi particular, the horizontal and vertical extent of the cloud, given by the model after 2 days of simulation, is found to be in good agreement with the remote and in situ measurements. An idealized tracer giving the time spent inside the type II PSC has also been introduced in the simulation. It is shown that about 60% of the vortex air at 470 K has passed through the PSC after 3 1/2 days of integration. Emphasis is put on a localized area situated downstream from the PSC and believed to be the most chemically perturbed air mass: the air parcels of this region have spent, after 3 days of integration, more than 50 hours at temperatures below the frost point and about 16 hours in sunlight. Since the largest discrepancy between the total ozone forecast and TOMS data is found in the same area, we discuss the possibility of a considerable chemical ozone destruction subsequent to the type II PSC formation. This localized destruction could reflect the high degree of chlorine activation and denitrification expected to occur immediately downstream of water‐ice PSCs.
Correlations between solar activity and the atmosphere: An unphysical explanation
Authors: Salby Murry L. , Shea Dennis J.
Published: February 2008

A wide array of atmospheric properties has recently been shown to be correlated to solar activity. The disparate behavior characterizing those properties makes their relationship to solar activity difficult to explain with a unified physical argument. Statistical considerations related to sampling and the length of records available to correlate atmospheric behavior against solar activity are able to explain several of the essential features of solar‐atmospheric correlations. Stratifying wintertime data according to the phase of the quasi‐biennial oscillation (QBO) leaves undersampled most of the variability in the polar stratosphere operating on quasi‐biennial time scales. Aliasing of low frequencies by that undersampled variability introduces spurious covariance that appears to be responsible for the dramatic increase in correlation when data are stratified according to the QBO. Correlations with unstratified data are not explained by aliasing from undersampled behavior. However, uncertainties in their interpretation and reliability leave these quantities open to question as well. The relatively short lengths of atmospheric records limit the ability of cross covariance properties to discriminate to solar activity and hence to distinguish such from other forms of interannual variability. Likewise, the discrete nature of the cross spectrum with solar activity admits only a few statistical degrees of freedom, which limits the reliability with which correlations can be determined. In fact, when the distribution of cross‐spectral power is taken into account, none of the correlations considered is significant. Coherence and correlation with sea level pressure both decrease with increasing record length and fall beneath the 90% level of statistical significance when records are extended back to the turn of the 20th century. The physical significance of such properties is considered in statistics generated from artificial solar variability, which demonstrate that behavior like that observed is not unique to the solar period. Over a wide range of period, false solar variability leads to correlations and coherences that are as high or higher than those produced by actual solar variability. A steady increase in these properties with false solar period suggests that time scales typical of solar activity are not represented in the limited atmospheric records adequately enough to permit a reliable calculation of covariance statistics.
Pyroxene spectroscopy revisited: Spectral‐compositional correlations and relationship to geothermometry
Authors: Cloutis Edward A. , Gaffey Michael J.
Published: February 2008

Pyroxene reflectance and transmittance spectra have been examined in a search for systematic relationships between spectral features and compositional variations and to assess the applicability of reflectance Spectroscopy to pyroxene geothermometry. Orthopyroxenes containing up to ∼11 % Wollastonite show a positive correlation between Fe2+ content and wavelength positions of the major absorption bands. Aluminum‐rich orthopyroxenes display absorption bands at lower than expected wavelengths. Spectral‐compositional relationships are more complex for clinopyroxenes, showing both positive and negative correlations between band positions and major cation abundances. These relationships are further complicated by the presence of significant amounts of other transition series elements such as Ti and Cr and by the presence of exsolved phases and compositional zonations. Even small‐scale exsolutions (<1 μm wide) seem to be sufficient to significantly alter spectral properties. Contours of the wavelength positions of band minima projected onto the pyroxene tetralateral generally exhibit concave downward shapes. The orientations of the contours relative to pyroxene geotherms are such as to effectively preclude the use of Spectroscopy to significantly constrain the temperatures of formation of pyroxenes.
A Simple Two‐Layered Model for Shoaling of the Eastern Mediterranean Pycnocline Due to Glacio‐Eustatic Sea Level Lowering
Authors: Rohling Eelco J.
Published: February 2008

A simple two‐layered model is developed to assess the depth of the permanent pycnocline in the eastern Mediterranean during glacial times. Shoaling of this pycnocline, from its present depth below the euphotic layer to a depth within that layer at glacial times, has been inferred from the planktonic foraminiferal record (Rohling and Gieskes, 1989). In this paper, a two‐layered model is applied to study the origin of the glacial shoaling of the permanent pycnocline. The model suggests that shoaling is due to glacial sea level lowering. Using literature‐based glacial salinity and inflow reduction values, the model yields an estimated depth of about 80 m for the glacial pycnocline. This estimate represents an upper depth limit, since the model discards possible differences in the basin's heat loss between glacial and interglacial times.
A 220,000‐Year Climatic Record for the East Equatorial Atlantic Ocean and Equatorial Africa: Evidence from Diatoms and Opal Phytoliths in the Zaire (Congo) Deep‐Sea Fan
Authors: Jansen J. H. F. , Van Iperen J. M.
Published: February 2008

Accumulation rates of microfossil associations are independent of each other and, in addition to percentages, give indispensable information about the significance of micropaleontological data. Marine diatoms reveal that coastal upwelling in the Zaire fan region was strong during glacial stages and weaker during interglacial stages. Oceanic upwelling was intense in stages 6 and 2 and at the stage 5d–5c transition but not in stage 4. The Benguela Current did not penetrate into the Gulf of Guinea during the last 220,000 years. The PhFD index, based on the contribution of freshwater diatoms and phytoliths, is a measure of aridity in equatorial Africa. The production in the low‐salinity river plume was high in the most humid periods on land and low when the continent was arid. On the long term, nutrient supply of the Zaire River to the ocean was probably larger in humid than in arid periods. Periods of strong seasonal variability in river fluxes and coastal upwelling coincide with arid intervals, except in the very humid interval with strong seasonal contrasts 35,000–20,000 years B.P.
Linear and nonlinear couplings between orbital forcing and the marine δ18O record during the Late Neocene
Authors: Hagelberg Teresa , Pisias Nick , Elgar Steve
Published: February 2008

Previous investigations of the response of Plio‐Pleistocene climatic records to long‐term, orbitally induced changes in radiation have considered a linear response of climate. While the second‐order statistics of power spectra and cross spectra provide necessary information on linear processes, insight into the nonlinear characteristics of Pliocene and Pleistocene climate is not provided by these statistical quantities. Second‐order statistics do not contain the phase information necessary to investigate nonlinear, phase‐coupled processes. Such information is provided by higher‐order statistical quantities. In particular, bispectral analysis indicates that nonlinear couplings are present in the climatic (radiative) forcing at the Milankovitch frequencies. Through a linear transfer, this forcing produces similar nonlinear couplings in deep‐sea sedimentary oxygen isotope records (ODP site 677 and DSDP site 607) from 1.0 to 0 Ma during the late Neogene. This analysis suggests that during the late Pleistocene, the dominance of the 100,000 year cycle in the climate record is consistent with a linear, resonant response to eccentricity forcing. In the period from 2.6 to 1.0 Ma, a change in the nature of the climatic response to orbital forcing is indicated, as phase couplings present in the isotopic time series are not similar to the phase couplings present in the insolation forcing. Third‐order moments (skewness and asymmetry) are used to quantify the shape of the climatic response. From 2.6 Ma to present, an increase in the asymmetry (sawtoothness) of the oxygen isotopic records is accompanied by a corresponding decrease in the skewness (peakedness) of the records. This indicates an evolution in the nature of the phase coupling within the climate system. These results may provide important constraints useful in development of models of paleoclimate.
Biogenic opal in Southern Ocean sediments over the last 450,000 years: Implications for surface water chemistry and circulation
Authors: Charles Christopher D. , Froelich Philip N. , Zibello Michael A. , Mortlock Richard A. , Morley Joseph J.
Published: February 2008

We present records of biogenic opal percentage and burial rate in 12 piston cores from the Atlantic and Indian sectors of the Southern Ocean. These records provide a detailed, quantitative description of changing patterns of opal deposition over the last 450 kyr. The striking regional coherence of these records suggests that dissolution in the deep sea and sediment pore waters does not obscure the surface productivity signal, and therefore these opal time series can be used in combination with other surface water tracers to make inferences about the chemistry and circulation of the Southern Ocean under different global climate conditions. Three broad depositional patterns can be distinguished. Northernmost records (39°–42°S latitude) are characterized by enhanced opal burial during glacial periods and strong 41 kyr periodicity. Records from cores just north of the present Antarctic Polar Front (46°–49°S) show even larger increases in opal burial rate during glacial intervals, but have variance concentrated in the 100 and 23 kyr bands. Southernmost records (51°–55°S) are completely out of phase with those to the north, with greatly reduced opal burial rates during glacial periods. Taken as a whole, the opal records show no evidence for the increased total Antarctic productivity predicted by recent geochemical models of atmospheric CO2 variability. The areal expansion of Southern Ocean sea ice over the present zone of high siliceous productivity provides one plausible explanation for the glacial‐interglacial opal patterns. The excess silica not taken up in this zone during glacial periods would contribute to greater nutrient availability and thus higher productivity in the subantarctic region. However, local circulation changes may act to modify this basic signal, possibly accounting for the observed differences in the opal variance spectra.
The global beryllium 10 cycle
Authors: McHargue L. R. , Damon P. E.
Published: February 2008

The cosmogenic radionuclide 10Be has generated much interest because of its potential as a tracer in the environment and applications to geology, archaeology, glaciology, and oceanography. Nevertheless, for 10Be to be useful as a tool in the Earth sciences its geochemical cycle as outlined below needs to be understood more fully. Beryllium 10 (t1/2 = 1.5 × 106 years) is mainly produced in the atmosphere by spallation of oxygen and nitrogen induced by secondary neutrons formed by cosmic ray interactions with the atmosphere, but some is produced in situ on the surface of the Earth. Deposition of 10Be onto the surface of the Earth depends primarily on precipitation. Deposited 10Be is made up of several components, primarily 10Be produced in the stratosphere and in the troposphere and 10Be recycled from dust and soil particles, and secondarily 10Be recycled from the ocean as hygroscopic nuclei and from cosmic dust. Even though paleoprecipitation dominated 10Be deposition at any one location in the past, cosmic ray flux and major changes in the Earth's magnetic field also influenced 10Be deposition. The 10Be deposited on land will either be fixed in soils or be carried away in overland flow through the fluvial system, or locked in ice. Most of the beryllium is transported in the sediment load and that which stays in solution shows a strong pH dependence and is highly mobile in organic‐rich continental waters. Beryllium 10 from sediments and river water is quickly deposited in the nearshore sediment along the coastlines along with a small amount of 10Be that is released and dispersed to the deep sea. In the open sea, most of the beryllium is in solution and the rest resides on particulate matter, much of which is of biogenic origin. Beryllium 10 that is added to the sea may be scavenged by such particles, but as they settle out into deeper waters the organic matter may oxidize and calcareous organisms may slowly dissolve, releasing 10Be back into solution, though fecal pellets may carry much of the 10Be to the seafloor. Slow‐growing manganese nodules absorb some 10Be directly from the surrounding water, but pelagic and slope sediments act as the ultimate sinks for 10Be as the residence time for 10Be in the sediments approaches that of the mean life of 10Be, 2.18 × 106 years. Nevertheless, a small portion of 10Be is subducted or accreted at the world's trenches, and it has been used as a tracer for the study of island‐arc volcanism.
The emergence of concurrent high‐resolution physical and bio‐optical measurements in the upper ocean and their applications
Authors: Dickey Tommy D.
Published: February 2008

Time and space scales of processes relevant to the upper ocean ecosystem span more than 9 orders of magnitude, consequently adequate sampling of the oceanic environment is a major challenge. However, new capabilities for studying upper ocean physical and bio‐optical processes have developed rapidly within the past decade with the advancement of sensor technology and data acquisition and storage capabilities. Several oceanic measurement systems have been designed recently to enable the collection of physical and bio‐optical data concurrently. Problems concerning variability in primary production by phytoplankton, upper ocean heating, small‐scale physical mixing and advection, the dispersion of oceanic discharges, and global scale climate change related to the carbon cycle can now benefit from in situ concurrent physical and bio‐optical data sets. The ocean sampling platforms utilized for deployment of these systems have included ships, the stable platform Research Platform FLIP, moorings and drifters. Examples of recent data sets obtained from these platforms are presented, and the merits of each of these sampling modes are described. In addition, the needs for complementary in situ and remotely sensed (for example, from satellites) data sets for both analytical and modeling efforts are summarized. Several research applications of the new technology are highlighted.
State of balance of the cryosphere
Authors: van der Veen C. J.
Published: February 2008

The current state of balance of the terrestrial ice sheets and glaciers is poorly known. What little data are available suggest that, worldwide, mountain glaciers have receded since about the mid‐nineteenth century, with occasional interruptions of the retreat. The interior part of the Greenland ice sheet appears to be thickening or in near equilibrium, but this ice sheet may be thinning in the coastal areas. Estimates of the mass balance of the Antarctic ice sheet suggest that it is positive, although the error limits allow for a slightly negative balance. There is an urgent need to greatly improve the current estimates and to monitor the ice sheets continuously for changes in volume and extent. A program based on satellite observation techniques, in cooperation with ground‐based surveys repeated over long time periods (many years or decades), appears to be most opportune to achieve this.
Mesospheric clouds and the physics of the mesopause region
Authors: Thomas Gary E.
Published: February 2008

During the last decade, new satellite observations of polar mesospheric clouds and ground‐based radar and lidar sounding of the high‐latitude summertime mesosphere have stimulated new interest in this highly unusual atmospheric region. Computer simulations indicate that the ice condensation model for mesospheric cloud formation is correct in broad outline. This review contains a brief historical account of early mesospheric cloud studies with an emphasis on the two main theories: cosmic dust and ice condensation models. Current topics are described, including wave‐cloud interactions, the dynamics and momentum budget of the high‐latitude polar mesosphere, new satellite observations, polar mesospheric summer radar echoes, heterogeneous chemistry, and implications of apparent secular changes in cloud brightness for global change of the atmosphere as a whole. There are major uncertainties in our theoretical understanding of the ice formation process, particularly in how the ice particles are nucleated. Future progress will require new research efforts in three separate directions: observations (ground based, rocket, and satellite), laboratory experiments, and theoretical modeling.
Mitigation against extreme windstorms
Authors: Golden Joseph H. , Snow John T.
Published: February 2008

This paper treats various manifestations of atmospheric wind in relation to the effects these have on human safety and comfort. We concentrate on more recent advances in our knowledge of the geophysical structure and behavior of extreme windstorms. Particular attention is given to severe thunderstorms and their attendant mesoscale offspring, tornadoes and downbursts, as well as the extratropical and tropical cyclones. It appears that the highest credible wind speed estimates in any of these windstorms so far are for tornadoes, about 135 m s−1; these have been derived from photogrammetric analyses of eyewitness photography and remote sensing from in situ and portable Doppler radars. On the other hand, it is found from extensive aerial and ground poststorm damage surveys that the vast majority of all tornadoes have peak wind speeds no higher than those measured by sparse surface networks and reconnaissance aircraft in mature hurricanes. New in situ and remote sensing (Doppler radars) weather observing networks currently being deployed across the United States and other countries, combined with greater public awareness, may significantly alter our current assessment of the climatology of extreme windstorms in these areas. Advances in the field of wind engineering are shown to afford cost‐effective techniques for mitigating against extreme windstorms, including tornadoes. However, the rather unique sociopolitical framework of building codes and practices in the United States presently hinders effective technology transfer and mitigation practice. Important implications of these findings accrue to forecasts and warnings of forest fires and airborne dispersal (loss of containment) of toxic materials, including nuclear processing by‐products.
Multispectral satellite data in the context of land surface heat balance
Authors: Choudhury Bhaskar J.
Published: February 2008

Any realistic study of the Earth's climate must consider thermal interaction between the atmosphere and the land surface. During the past few years, several highly sophisticated models have been developed to describe exchanges of radiation, heat, and momentum between the land surface and the atmosphere at mesoscales and global scales. These models need to be supplemented by high‐quality global measurements at varying spatial and temporal scales of physical and biological states of the land surface. Global data sets are needed for surface parameters used to describe the processes and also to initialize and validate the time evolution of surface characteristics predicted by the model. Observations in different spectral bands by instruments on board satellites can provide spatially representative values for some of the fluxes and radiative characteristics of the surface, from which the parameters needed for heat balance modeling have to be derived. Development of these data sets presents considerable difficulty because the relations between radiative and physical characteristics are generally nonlinear and nonunique; the radiative characteristic in any spectral band is generally determined by several physical characteristics. Relationships between different spectral observations can be used to develop hypotheses concerning the relative importance of different land surface parameters determining these observations, which would have to be confirmed by field observations. Satellite observations for visible, near‐infrared, infrared, and microwave bands to estimate the fluxes at the surface (radiative, soil, sensible, and latent heat) and surface characteristics (albedo, surface temperature, vegetation parameters, and soil moisture) are presented. Interannual variations of some of these satellite observations are discussed in relation to land surface change. A better understanding needs to be developed regarding the interpretation of infrared temperature observations as they relate to the temperature determined by the heat balance equation. Further study is needed to explore more effective use of remotely sensed data for vegetation in heat balance modeling.
On the location of causative atmospherics of very low latitude whistlers and their magnetospheric propagation mechanism
Authors: Hayakawa M. , Shimakura S. , Moriizumi M. , Ohta K.
Published: February 2008

The purpose of this paper is to locate the causative atmospherics of very low latitude whistlers whose ionospheric exit regions have previously been determined at geomagnetic latitudes, 10°–13°, in order to aid our understanding of the magnetospheric propagation mechanism of very low latitude whistlers. It is found that the causative atmospherics of very low latitude whistlers are very widely distributed in a range from 500 to ∼2500 km from the conjugate point of whistler ionospheric exit region previously determined. This fact lends further support to our previous implication that magnetospheric preferred paths supporting field‐aligned propagation are extremely rare in occurrence and that there has existed a preferred and stable magnetospheric path in a very restricted location on the day of high whistler activity.
Efficient analysis of planar scattering problems with multiple excitations using equivalent incident currents
Authors: Kastner Raphael
Published: February 2008

Large planar scatterers can be analyzed either by a direct moment method scheme, leading to block Toeplitz matrices for certain geometries, or via iterative techniques. In any case the physical optics component of the solution is readily known, hence the burden of its computation should be eliminated. An inherent separation between the physical optics and the remaining “fringe current” components is achieved by the use of the equivalent current representation of the incident fields. This representation has been beneficial in the recently introduced “add‐on” scheme, as well as other methods based on modular computations. In this work it is used to provide an extra degree of efficiency to the analysis of electromagnetic scattering problems from planar structures with many incident fields. The approach extends the capability of a recently introduced method whereby a class of incident electric fields is represented by a set of basis functions. Here the equivalent incident current is expanded into a set of basis functions restricted to a limited aperture region only, facilitating the computation of the fringe current only. The response to any incident field is synthesized subsequently from the responses to these excitations. This results in a stable scheme which can efficiently treat large problems with many excitations.
A unified perturbation expansion for surface scattering
Authors: Rodríguez Ernesto , Kim Yunjin
Published: February 2008

Starting with the extinction theorem, we present a perturbation expansion which, to first and second orders, converges over a wider domain than the small perturbation expansion and the momentum transfer expansion. We show that, in the appropriate limits, both of these theories, as well as the two‐scale expansion, are recovered. There is no adjustable parameter, such as a spectral split, in the theory. We apply this theory to random rough surfaces and derive analytic expressions for the coherent field and the bistatic cross section. Finally, we present a numerical test of the theory against method of moments results for Gaussian random rough surfaces with a power law spectrum. These results show that the expansion is remarkably accurate over a large range of surface heights and slopes for both horizontal and vertical polarization.
Ground‐based observations of atmospheric radiation at 5, 10, 21, 35, and 94 GHz
Authors: Mätzler Christian
Published: February 2008

Atmospheric observations made with ground‐based, multifrequency radiometers (f = 4.9, 10.4, 21, 35, and 94 GHz) for the original purpose of microwave signature research for remote sensing of snowpacks, sea ice, and vegetation were analyzed. The tipping‐curve method was used both for radiometric calibration and for the determination of the zenith opacities. The data were grouped into three regions with different locations and different altitudes (10, 570, and 2550 m) above sea level. Key parameters are air temperature and atmospheric zenith opacities at each frequency. The large number of different (nonprecipitating) conditions provide statistical properties of atmospheric attenuation. Especially high correlation was found between the opacities at 35 and 94 GHz. For cloudless subsets of the data these opacities are also highly correlated with the ones at 21 GHz. Estimation of the total atmospheric contents of water vapor V and cloud liquid water L was made from the opacities at 21, 35, and 94 GHz. Whereas V is clearly correlated with the surface air temperature, large L values are clustered around temperatures near 0°C. Comparison with radiosonde measurements indicates a standard deviation in V of 0.22 cm and a bias of −0.11 cm. Consistency tests of liquid water estimates show a standard deviation of 0.03 mm.
Crustal structure and the mechanism of extension in the northern Red Sea: Constraints from gravity anomalies
Authors: Cochran James R. , Gaulier Jean‐Michel , Le Pichon Xavier
Published: February 2008

Gravity data from detailed marine surveys were used to investigate the density structure of the crust and upper mantle beneath the northern Red Sea, a continental rift considered by many to be in the process of establishing a mid‐ocean ridge type spreading center. A gravity and bathymetry profile across the sea near 27°N was analyzed in detail. Model constraints include single‐channel and multichannel seismic reflection lines coincident with the gravity profile, which provide detailed information on sedimentary layers, a series of ESP seismic experiments centered nearly on the gravity line which constrain the sediment and crustal thickness, and a series of 58 closely spaced heat flow measurements nearly coincident with the gravity line which closely constrain the mantle thermal structure and thus density variations within the mantle. The calculated gravity anomalies based on the known crustal and mantle structure fail to match the observed data. Specifically, the model anomalies become steadily more negative from the margins toward the center of the sea with the result that the calculated gravity is approximately 25 mGal more negative near the axis relative to the marginal areas than are the observed anomalies. Two possible solutions were investigated. One is to introduce a lower crustal layer resulting from crustal underplating within what was originally considered to be the upper mantle beneath the marginal areas. The other is to introduce an area of slightly denser crust resulting from intrusion of new mafic crustal material within the axial depression. Both solutions can reproduce the observed gravity anomalies within the Red Sea. However, the complete set of geophysical data, and in particular the heat flow in the Red Sea and gravity and seismic refraction data on land, suggests that the most satisfactory model is that the crust of the axial depression is denser than that of the marginal areas. This implies that crustal extension in the northern Red Sea is presently occurring in large part by intrusion of new mafic material.
Tectonics of Mid‐Tertiary Extension along a transect through west central Arizona
Authors: Spencer Jon E. , Reynolds Stephen J.
Published: February 2008

Large‐magnitude Miocene extension in west central Arizona occurred primarily along three imbricate, northeast dipping normal faults. The structurally highest of these faults, the gently dipping Buckskin‐Rawhide detachment fault, accommodated approximately 66 km of crustal extension, whereas the two structurally lower faults accommodated a total of about 20 km extension. Due to this large‐magnitude extension, an area at the Earth's surface that was 10 to 20 km wide is now over a 100 km wide, and crystalline rocks with mid‐Tertiary mylonitic fabrics, uncovered by detachment faulting, are exposed over roughly 2000 km² in the Harcuvar metamorphic core complex. Most of the upper plate of the Buckskin‐Rawhide detachment fault was largely undeformed by internal extension; only the thin, tapered end of the upper plate was highly extended. During extension the lower plate must have flexed to conform to the listric underside of the upper plate and to have flattened to its present subhorizontal form as it was uncovered. Grooves on the underside of the upper plate were apparently imposed on the pliable lower plate as it was denuded, forming extension‐parallel folds in the lower plate. Low flexural strength characterized the lower plate during denudation, and a highly mobile, low‐viscosity deeper crust must have effectively decoupled the upper crust from the mantle lithosphere.
Late Cenozoic kinematics of the Calabrian Arc, southern Italy
Authors: Knott Steven D. , Turco Eugenio
Published: February 2008

Based on structural analysis, seismicity, and paleomagnetic data a model is presented for the late Cenozoic kinematics of the southern Italian mountain belt. The model predicts that late Cenozoic deformation of the internal part of the belt involved extension and lateral bending of the mantle and lower crust and that in the upper crust faulting was accompanied by semirigid block rotation. In the external part of the belt thrusting dominated. In the north where the arc joins up with the southern Apennines regional shear was dominantly left lateral and distributed between left‐slip along WNW trending cross faults, a component of right‐slip on north to NNE trending extensional faults, and counterclockwise rotation of upper crustal blocks, including the basin fill and north to NNE trending basin margin faults. In the southern part of the arc, overall right lateral shear was accommodated by right‐slip on WNW trending cross faults, a component of left‐slip on NE trending extensional faults, and clockwise rotation of upper crustal blocks, basins, and NE trending faults. These styles of deformation were probably confined to the upper plate of the Tyrrhenian subduction system. They are considered to have been active from the beginning of extension in the Tyrrhenian Basin (circa 11 Ma) and are still active today (based on recent seismicity).
A possible southeastern extension of the Midcontinent Rift System located in Ohio
Authors: Dickas Albert B. , Mudrey M. G. , Ojakangas Richard W. , Shrake Douglas L.
Published: February 2008

In 1988 a stratigraphic test core drilled in southwestern Ohio penetrated a previously unknown structure and sedimentologic unit. Core analyses disclosed a sequence of lithic arenite and siltstone of probable pre‐Phanerozoic age, deposited within an alluvial‐fluvial environment. A seismic reflection profile across the core site shows a sequence of strong, horizontal Paleozoic reflectors unconformably overlying eastward dipping, layered units of poor reflectivity. Beyond the core hole total depth, a regime of excellent reflectors is seen. The pre‐Mount Simon (Upper Cambrian) sedimentary sequence encountered has been defined as the type section of the Middle Run Formation. Point counter analyses of typical Middle Run Formation samples indicate that this sequence is similar in composition to middle Proterozoic units associated with the Midcontinent Rift System in the Lake Superior region. The newly discovered structure in Ohio is also similar to half‐graben structures composing the Lake Superior Basin portion of the Midcontinent rift. On the basis of similarities in lithology, stratigraphy, structure, and proximity to regional gravity anomalies, the Middle Run Formation and its apparent half‐graben basin is proposed as evidence for the probable extension of the Midcontinent Rift System southward, from its normally accepted termination in southeastern Michigan, into southwestern Ohio.
Deep seismic profile of the Amazonian Craton (northern Brazil)
Authors: de Matos Renato M. D. , Brown Larry D.
Published: February 2008

Deep seismic profiling of the Amazonian craton (northern Brazil) reveals previously unknown deep structural features buried beneath a thin, relatively flat Phanerozoic sedimentary cover (Amazon basin). The seismic signature of the Precambrian crust is characterized by a transparent shallow basement down to 8–9 km followed by a highly reflective middle and lower crust. Middle and lower crustal events are dominated by abundant dipping, asymmetric arcuate reflections and diffractions, the shallowest of which occur beneath a structural arch (Jutaí arch). Although wide angle refraction data are unavailable, a decrease in the number of coherent reflections at about 15 s two‐way travel time (45 km) and small drops in amplitude and increases in average frequency are interpreted to mark the Moho. The deep Amazonian seismic line is located near the westernmost boundary of the Amazonian craton, imaging the Rondonian province, one of the youngest geochronological provinces of the craton (middle Proterozoic). To the south, the Rondonian basement crops out, revealing schists, gneisses, granulites, and important volumes of anorogenic granites. The prominent, laterally extensive arcuate reflections observed within the middle and lower crust may be related to this anorogenic magmatic activity, perhaps corresponding to layered intrusive complexes. On the other hand, intrusion of mantle derived material during an early Paleozoic rifting, as well as the Mesozoic episodes of mafic intrusion may also have contributed to this seismic signature. Similar seismic signatures found in eastern Australia and on COCORP profiles of the central U.S. craton suggest that such cratonic terranes may have undergone similar tectonic evolution. In the upper crust, probable fault plane reflections associated with ENE‐WSW reverse faults of Jurassic‐Early Cretaceous age may sole into the top of the reflective zone, suggesting that the lower limit of the transparent upper crust may represent a rheological boundary.
Emissions of light nonmethane hydrocarbons from the Atlantic into the atmosphere
Authors: Plass‐Dülmer C. , Khedim A. , Koppmann R. , Johnen F. J. , Rudolph J. , Kuosa H.
Published: February 2008

During two Atlantic cruises of the German research vessel Polarstern, 1988 and 1989, the concentrations of light nonmethane hydrocarbons (NMHC) in seawater were measured. On the basis of a simple budget analysis, the oceanic mixed layer represents a NMHC reservoir with an internal production and a major loss by emission into the atmosphere. As a consequence, the concentrations of NMHC depend on the rates of ocean‐atmosphere exchange: high exchange rates reduce the concentrations and vice versa. With the prevailing transfer velocities the emission rates were calculated according to ocean‐atmosphere exchange models. The regional averages of the alkene emission rates vary by 1 order of magnitude. For ethene the maximum value was 5×108 molecules cm−2 s−1. The emissions of the various alkanes were generally below 1×108 molecules cm−2s−1. The total C2‐C4 hydrocarbon emissions during both cruises average 6×108 molecules cm−2 s−1, 70 % of which are alkene emissions, with ethene alone contributing 42 % to the total. No indications for enhanced emissions of NMHC at high phytoplankton concentrations or in the proximity to coastlines were observed. Thus we regard the emissions as representative for the mid‐Atlantic and the season of the investigations, August to October. The calculated emission rates of the shortlived alkenes are validated by comparison with atmospheric measurements of NMHC. The emission rates are substantially lower than the majority of reported oceanic emission estimates by up to about 2 orders of magnitude.
Detecting the aerial fertilization effect of atmospheric CO2 enrichment in tree‐ring chronologies
Authors: Graybill Donald A. , Idso Sherwood B.
Published: February 2008

The growth‐promoting effects of the historical increase in the air's CO2 content are not yet evident in tree‐ring records where yearly biomass additions are apportioned among all plant parts. When almost all new biomass goes into cambial enlargement, however, a growth increase of 60% or more is observed over the past two centuries. As a result, calibration of tree‐ring records of this nature with instrumental climate records may not be feasible because of such growth changes. However, climate signals prior to about the mid‐19th century may yet be discovered by calibrating such tree‐ring series with independently derived proxy climate records for those times.
A regional estimate of convective transport of CO from biomass burning
Authors: Pickering Kenneth E. , Scala John R. , Thompson Anne M. , Tao Wei‐Kuo , Simpson Joanne
Published: February 2008

We present a regional‐scale estimate of the fraction of biomass burning emissions that are transported to the free troposphere by deep convection. The focus is on CO and the study region is a part of Brazil that underwent intensive deforestation in the 1980's. The method of calculation is stepwise, scaling up from a prototype convective event, the dynamics of which are well‐characterized, to the vertical mass flux of carbon monoxide over the region. Satellite‐derived observations of the area extent of pollution from biomass burning and convective cloud cover are used in the scaling.

Given uncertainties in CO emissions from biomass burning and the representativeness of the protoype event, it is estimated that 10–40 percent of CO emissions from the burning region may be rapidly transported to the free troposphere over the burning region. These relatively fresh emissions will produce O3 efficiently in the free troposphere where O3 has a longer lifetime than in the boundary layer.
Electron microscope studies of aerosol layers with likely Kuwaiti origins over Laramie, Wyoming during spring 1991
Authors: Sheridan Patrick J. , Schnell Russell C. , Hofmann David J. , Harris Joyce M. , Deshler Terry
Published: February 2008

Upper tropospheric aerosols observed in spring 1991 over Laramie, Wyoming, were sampled using balloon‐borne cascade impactors. Three impactor samples were collected; two were in upper tropospheric aerosol layers and one was collected at the same altitude in cleaner, “background” upper tropospheric air. Optical particle counters measured concentrations of particles with radii ≥ 0.15 μm in the layers which were increased 5–10 times over what is normally observed at these altitudes. Electron microscope analyses showed acidic and neutralized sulfate particles to be the dominant aerosol constituents in these layers, although carbonaceous soot aggregates and crustal dust particles were also found. The morphology and elemental composition of these particles closely resembled particles collected in the large mixed smoke plume of the Kuwaiti oil fires. Meteorological analyses showed favorable transport conditions from the Middle East to the continental U.S. when layers were present over Wyoming, and less than ideal conditions when the layers were absent. Based on these microanalytical results and the corroborating meteorological and air trajectory analyses, the most likely source of these aerosol layers is the oil fires in Kuwait.
The contribution of ion‐cyclotron waves to electron heating and SAR‐arc excitation near the storm‐time plasmapause
Authors: Thorne Richard M. , Horne Richard B.
Published: February 2008

The excitation of SAR arcs requires the transfer of energy from the energetic storm‐time ring current ions to tonal electrons located just inside the plasmapause. A recent observational study has indicated that Coulomb scattering with energetic O+ can at times provide sufficient electron hearing to maintain the energy dissipated in SAR arcs, but the question of how this energy is transported to the ionosphere remains unresolved. We demonstrate here that ion‐cyclotron waves can play an important role in both the energy transfer to plasmaspheric electrons and the subsequent downward heat conduction to SAR arc altitudes. Specifically such waves can experience enhanced path integrated amplification along the steep plasmapause density gradient; the later tends to keep the wave normal angle small on several successive bounces across the equator, thus allowing repeated cyclotron‐resonant amplification leading to a total gain of up to 20 e‐foldings. Subsequently, when the wave propagation vector becomes highly oblique, absorption occurs during Landau resonance with thermal plasmaspheric electrons. This increases the electron temperature in the direction parallel to the ambient field and leads directly to heat conduction into the ionosphere.
Determination of E region effective recombination coefficient using impulsive precipitation events
Authors: Nygrén T. , Kaila K. U. , Huuskonen A. , Turunen T.
Published: February 2008

A set of sudden increases followed by slow decay has been observed in E region electron density on December 17, 1990 using the EISCAT UHF‐radar. Simultaneous photometer observations indicate that the density enhancements are caused by impulsive particle precipitation with short duration (4 ± 1 s). Effective recombination coefficient profiles in the E region are calculated from decaying electron densities using the continuity equation, and the results are compared with previous observations. It is pointed out that short‐lived particle precipitation affects the ion composition in the E region and therefore the effective recombination coefficient in this situation is different from the steady‐state value.
Local thermodynamic equilibrium of carbon dioxide in the upper atmosphere
Authors: Rodgers C. D. , Taylor F. W. , Muggeridge A. H. , López‐Puertas M. , López‐Valverde M. A.
Published: February 2008

The rotational and vibrational temperatures of the v2 and 2v2 modes of carbon dioxide in the upper atmosphere have been derived from transmission spectra measured by the ATMOS instrument on Spacelab 3 over the height range 60–110 km. The rotational and vibrational temperature profiles are found to be nearly identical, which leads to the conclusion that the CO2 (v2) level is in local thermodynamic equilibrium (LTE) within the experimental errors up to 95 km, and very nearly so to at least 110 km. The CO2 (2v2) level is found to be close to LTE up to at least the upper height limit of its retrieval, i.e., 93 km. The interpretation of those measurements using a non‐LTE model [López‐Puertas et al., 1986] supports a fast rate for the deactivation of CO2(v2) by atomic oxygen, similar to that derived by Sharma and Wintersteiner [1990]. This provides independent confirmation, from a qualitatively different type of measurement, of the conclusion of those authors that the radiative cooling of the upper atmospheres of the Earth is around an order of magnitude greater than our 1986 model predicted. It also has implications for thermospheric cooling on the other terrestrial planets, as well as expanding the possibilities for future remote sensing of the temperature of the upper mesosphere and lower thermosphere, since the upper limit which can be sounded is higher than previously believed.
Combined use of 50 MHz and 915 MHz wind profilers in the estimation of raindrop size distributions
Authors: Currier P. E. , Avery S. K. , Balsley B. B. , Gage K. S. , Ecklund W. L.
Published: February 2008

To estimate raindrop size distributions aloft, we fit a theoretical Doppler spectrum of a model drop size distribution to observed Doppler power spectra measured by a 915 MHz profiler, while using concurrent information supplied by a 50 MHz profiler to correct for vertical winds. While several assumptions have been made in deriving the theoretical Doppler spectrum, model derived rainfall rates compare favorably with locally measured rainfall rates obtained from rain gauge estimates.
Multiple‐SCS technique for measuring anisotropy in the mantle
Authors: Vinnik Lev P. , Farra Véronique
Published: February 2008

We describe a technique for measuring shear wave splitting in the mantle of the oceans and poorly instrumented continental regions. The idea of the method is to analyse evolution of the form of the particle motion in the long‐period multiple ScS and sScS phases as a function of the order of reflection. The differential motion is inverted into the parameters of azimuthal anisotropy. The technique is applied to the digital recordings of events from the Tonga‐Kermadek seismic zone at station AFI. It is found that the fast direction of anisotropy in the mantle beneath the Pacific plate is close to the present day absolute‐velocity direction of the plate.
Progress in the determination of the gravitational coefficient of the Earth
Authors: Ries J. C. , Eanes R. J. , Shum C. K. , Watkins M. M.
Published: February 2008

In most of the recent determinations of the geocentric gravitational coefficient (GM) of the Earth, the laser ranging data to the Lageos satellite have had the greatest influence on the solution. These data, however, have generally been processed with a small but significant error in one of the range corrections. In a new determination of GM using the corrected center‐of‐mass offset, a value of 398600.4415 km3/sec2 (including the mass of the atmosphere) has been obtained, with an estimated uncertainty (1 σ) of 0.0008 km3/sec2.