bluuebunny/crossref_metadata_2025 huggingface dataset:
Estimating errors in fractional cloud cover obtained with infrared threshold methods
Authors: Chang Fu‐Lung , Coakley James A.
Published: February 2008

Differences between spatial coherence and infrared threshold derived cloud cover were used to estimate errors in cloud cover that arise through the application of thresholds to imagery data. The differences indicated that threshold errors could be predicted by assuming that the cloud cover at the scale of a typical satellite imagery pixel (4–8 km) is uniformly distributed between some small value δ (δ < 0.2) and 1 − δ. In this study, results were obtained for single‐layered cloud systems from four oceanic regions. Cloud cover was analyzed for both (60 km)2 and (250 km)2 regions. Three distinct infrared thresholds were used: (1) a “cloud‐free threshold” for which the threshold was set slightly below the radiance observed for cloud‐free pixels in the region; (2) an “overcast threshold” for which the threshold was set just above the radiance observed for pixels that were overcast in the region, and (3) a “midpoint threshold” for which the threshold was set midway between the radiances observed for cloud‐free and overcast pixels. For the cloud‐free threshold, cloud cover was overestimated; for the overcast threshold, cloud cover was underestimated, and for the midpoint threshold there was relatively little difference between the threshold and spatial coherence derived cloud cover. Mean differences in cloud cover were as large as 0.25 for (60 km)2 regions and 0.18 for (250 km)2 regions. Mean and rms differences reached maximum values when the regional cloud cover was 0.5. The fraction of 4‐ to 8‐km imager pixels that were neither cloud free nor overcast was approximately 0.5. Furthermore, when the regional cloud cover (60–250 km) was small, the cloud cover in partially covered imager pixels was also small; likewise, when the regional cloud cover was large, the cloud cover in partially covered imager pixels was also large. This connection between regional scale cloud cover and 4‐ to 8‐km pixel scale cloud cover suggests a link between large‐scale fields which govern the regional cloud cover and the small‐scale disturbances to the large‐scale fields, which must govern the pixel scale cloud fraction.
Interaction of katabatic flow with local thermal effects in a coastal region of Adelie Land, east Antarctica
Authors: Pettré Paul , Payan Christophe , Parish Thomas R.
Published: February 2008

Katabatic flows largely dominate the climate of the Adelie Land coastal region. A detailed climatological data analysis of Dumont d'Urville has been conducted. Results of this study support the idea that katabatic flow can be locally enhanced by the diurnal cycle of solar insolation and the temperature contrast between the continent and the ocean. The interaction between katabatic wind and local thermal effects is expressed in terms of scale analysis. Except for surface stress, all terms in the momentum equation for a katabatic flow in a coastal region of Antarctica can reach the same order of magnitude. The local circulation then is the result of a relatively tenuous force balance which can be disrupted even by a weak perturbation of any term. To estimate the effect of the temperature contrast between the ocean and the continent on the katabatic flow, two numerical experiments have been conducted. The simulations consider an ocean free of sea ice representative of the summer months, and another winter case with the ocean covered by thick sea ice. These simulations show that with the ocean free of sea ice, the katabatic flows extend only a limited distance over the open ocean during the day due to the local thermal effects. With the ocean covered by sea ice, the katabatic winds are not constrained and extend a considerable distance offshore.
Introduction to the special section on magma oceans
Authors: Agee Carl B.
Published: February 2008

One view of planetary evolution proposes that Earth, the Moon, and possibly other “terrestrial” bodies have experienced high‐temperature conditions during their formation. The high temperatures, sufficient to melt silicates, metals, and sulfides, possibly to mantle or core depths, result in a planet‐wide “magma ocean.” Not surprisingly, the nature of planetary differentiation is expected to be greatly influenced by the existence of an early magma ocean. For instance, a terrestrial body of a given bulk composition and size that was initially molten should solidify with a characteristic crust, mantle, and core.
Rates of oxidative weathering on the surface of Mars
Authors: Burns Roger G. , Fisher Duncan S.
Published: February 2008

The presence of sulfates and ferric‐bearing assemblages in the Martian regolith implies that oxidative weathering of iron‐ and sulfur‐bearing minerals has occurred through time on the surface of Mars. A model of acid weathering has been proposed for the iron‐rich basalts on Mars. In this model, aqueous oxidation of iron sulfides released SO42− and H+ ions that initiated the dissolution of basaltic ferromagnesian silicates and released Fe2+ ions. The Fe2+ ions eventually underwent ferrolysis reactions and produced insoluble hydrous ferric oxide phases. Measurements of the time‐dependence of acid weathering reactions have shown that pyrrhotite (Fe7S8) is rapidly converted to pyrite (FeS2) plus dissolved ferrous iron, the rate of pyrite formation decreasing with rising pH and lower temperatures. The rate of oxidation of aqueous Fe2+ ions derived from weathering of iron sulfides by dissolved atmospheric oxygen is known to be pH‐dependent; rates are fast above pH 4.5 at ambient temperatures on the Earth's surface and much slower in acidic groundwater. On Mars, oxidation rates of dissolved Fe2+ ions in equatorial melt‐waters in contact with the atmosphere (PO2 = 10−5 atm) are estimated to lie in the range 0.3–3.0 ppb Fe yr−1 over the pH range 2 to 6. These oxidation rates are more than 105 times slower than corresponding reactions near the freezing point of water on Earth. Oxidation of Fe2+ ions is estimated to be extremely slow in brine eutectic solutions that might be present on Mars and to be negligible in the frozen regolith. Such slow oxidation rates of aqueous Fe2+ ions in acidic groundwater (now permafrost) during the evolution of the Martian regolith would aid the stability, solubility and transport of iron in solution and other dissolved species over the surface of Mars.
Magma ocean formation due to giant impacts
Authors: Tonks W. Brian , Melosh H. Jay
Published: February 2008

Current understanding of the last stages of planetary accretion suggests that mass and energy accumulation are dominated by a few large impacts. An important thermal consequence of such impacts is melting and formation of a large melt pond. If the planet's isostatic adjustment time scale is short compared to the magma pond's cooling time scale, the melt may be extruded onto the surface and form a magma ocean of approximately uniform depth. Although a giant impact striking at 10–15 km s−1deposits enough energy to melt the entire planet, the distribution of that energy is important in determining the thermal outcome of the collision. We examine the thermal effects of giant impacts by estimating the melt volume generated by the initial shock wave and corresponding magma ocean depths. Additionally, we examine the effects of the planet's initial temperature on the generated melt volume. The Hugoniot curve plotted in pressure‐entropy space is used to determine the shock pressure required to completely melt the material. For room temperature dunite, this pressure is about 150 GPa and the partial melt region is narrow. For dunite initially at the solidus temperature, this pressure is about 115 GPa. The partial melt region extends throughout the planet. Once the melting pressure is known, an impact melting model based on the second Hugoniot equation, the linear shock‐particle velocity relationship, and the empirical particle velocity‐distance relationship is used to estimate the radial distance melting occurred from the impact site. Once the distance is found, the melt region's geometry determines the associated melt volume. Partial melt volume is also estimated. The melt fraction that is not excavated during crater formation is estimated and magma ocean depths resulting from both excavated and retained melt are calculated. The model is also used to estimate the fraction of a planet melted by the initial shock wave. Nominal conditions of the Moon‐forming giant impact (projectile/planet mass = 0.14, impact speed = 15 km s−1) generate melting of 30–65% of the planet depending on its initial temperature. Whole planet melting requires projectile/planet mass ratios of > 0.4 for a 15 km s−1impact if the planet was near its solidus before the impact. Isostatic relaxation may generate a significant volume of additional melting.
Mars atmospheric winds indicated by motion of the Viking landers during parachute descent
Authors: Seiff A.
Published: February 2008

Winds in the Martian atmosphere at altitudes from 1.5 to 3.5 km have been determined from parachute descent trajectories of the two Viking landers. Viking 2 reached equilibrium with nearly steady winds of ∼8 m/s to the southeast below 3.3 km at 1000 LT. Viking 1 winds at 1615 LT rotated clockwise with decreasing altitude but were generally to the northwest at ∼20 m/s. At 1.5 km, the Viking 1 wind direction was close to that measured by the landed anemometer at the same local time, while at the Viking 2 site, wind direction at 1.5 km was nearly opposite that near the surface. This is consistent with the fact that Viking 1 descended within a vigorously convective boundary layer, while Viking 2 at 1.5 km was above the boundary layer. Turbulent velocities in the Viking 1 boundary layer were ∼3 m/s. Mean upflow velocity was ∼1 m/s. The Viking 2 atmosphere was relatively quiescent, with orderly wind directional variation possibly suggesting the presence of waves. Comparison of the measured winds with a recent global circulation model showed little or no correspondence, probably an indication that the winds were locally controlled. The boundary layer, slope‐wind model of Haberle et al. (1993), with ground slope adjusted to give best fit to these and landed meteorology data, gave roughly the wind direction and the observed magnitude within a factor of ∼2, but with opposite rotation of the wind vector with altitude. The ground slopes deduced are consistent with terrain observed in approach to the Viking 1 landing, and do not conflict with the less definitive terrain data at the Viking 2 site. The high sensitivity of winds at altitudes up to several kilometers to terrain slopes as small as a few meters per kilometer would suggest that slope winds may be widely found in the lowest few kilometers of Mars atmosphere.
An analysis of the history of dust activity on Mars
Authors: Martin Leonard J. , Zurek Richard W.
Published: February 2008

A new comprehensive list of possible and probable dust activity has been compiled from various published lists and additional data. All previously listed events have been reviewed and evaluated. For uniformity and clarity, each event is classified using a new system that includes a well‐defined nomenclature. Maps showing the reported locations of individual major events, as well as a summary map of the smaller “local” events, have been compiled. Detailed commentaries describe the events and/or circumstances of their observation. The seasonal distribution of Martian dust events is diagrammed and discussed together with a seasonal and annual (Mars years) timeline that includes the frequency of photographic coverage. The new compilation shows that major dust storms have originated in many different regions across the planet, with some evidence of more activity in the southern hemisphere generally and in specific regions like Hellas. Regional dust storms have been observed in nearly all seasons, except for two relatively narrow periods which occur near times when the polar caps have reached their maximum/minimum extent. Regional dust storms tend to occur most frequently, and all planet‐encircling dust storms have been observed during the southern spring and summer seasons, although there is significant interannual variability.
Microcraters on Mars: Evidence for past climate variations
Authors: Vasavada Ashwin R. , Milavec Thomas J. , Paige David A.
Published: February 2008

Mars climate models predict hundredfold or greater variations in the mass of the Martian atmosphere due to large amplitude variations in Mars' obliquity through time. The production rates of impact craters on the Martian surface should be greatly affected by these atmospheric mass variations. We have constructed a simulation of the meteor bombardment of Mars which shows that during periods of the lowest theoretical atmospheric mass, the production rates of centimeter‐sized hypervelocity impact craters are increased significantly. These results imply that limited in situ observations of microcraters visible on Martian rock faces could validate major aspects of the astronomical theory for climate change on Mars.
Higher temperatures and lower oceanic pCO2: A climate enigma at the end of the Paleocene Epoch
Authors: Stott Lowell D.
Published: February 2008

One of the largest and most abrupt climatic warming events documented in the geologic record occurred at the end of the Paleocene epoch. Oceanic deep waters warmed to 10°C, and high‐latitude surface waters warmed from ∼10°C to ∼20°C within several thousand years. This coincided with weakened atmospheric circulation and the extinction of ∼50% of deep‐sea benthic foraminiferal species. It has been suggested that this warm excursion was forced by higher atmospheric pCO2 and greenhouse effects caused by a pulse of hydrothermal activity and/or volcanism. Stable isotopic evidence is presented from two widely separated locations that suggest this warming was associated with a drop in oceanic pCO2 rather than an increase. Oceanic pCO2 change across this event was estimated using a model of 13C fractionation in photosynthate organic carbon versus [CO2aq], with solubility constants for CO2 and stable isotopic paleotemperature estimates. To derive a well‐preserved record for surface ocean δ13C change the organic carbon bound within the calcite lattice of well‐preserved planktonic foraminifera was extracted for isotopic analysis. With allowance for uncertainty in the isotopic differences between phytoplankton and foraminiferal organic matter, the initial results indicate a drop in surface ocean pCO2 at high and low latitudes from 600–700 parts per million (ppm) to ∼200 ppm. Lower pCO2 persisted for at least 10,000 years. The duration of the pCO2 excursion was long enough for the ocean and atmosphere to have reached a new steady state condition. There is no evidence of increased organic carbon burial in the deep sea during this period. Two alternative explanations are presented to account for such a rapid drop in oceanic pCO2. One involves reduced upwelling induced by diminished wind stress as atmospheric circulation weakened in response to climate warming. This would have reduced the rate of metabolic CO2 recycling into the surface ocean. It will be necessary to obtain data from regions outside potential upwelling zones in order to evaluate this. The second involves a readjustment of carbonate equilibria in the ocean to higher [CO3=] in the surface ocean, particularly at high latitudes where surface waters warmed to approximately 20°C. Such a shift in carbonate equilibria would have lowered the ocean's capacity to take in CO2. If the initial results presented here do accurately reflect a change in the global ocean [CO2aq], the Paleocene/Eocene boundary event may provide clues about the ocean's physical and biological response to rapid, large‐scale perturbations in atmospheric pCO2 and to global warming.
Oxygen Isotopic Composition of Multiple Species of Planktonic Foraminifera: Recorders of the Modern Photic Zone Temperature Gradient
Authors: Ravelo A. C. , Fairbanks R. G.
Published: February 2008

Abundances of 12 species of planktonic foraminifera collected in two plankton tows from the east tropical Atlantic are compared to the chlorophyll content and the temperature of the sea water from which they were collected. As expected from previous work in the tropics, all dominant tropical species occur in greatest abundance within the photic zone. Many species occur in greatest abundances in the seasonal thermocline in association with the maximum chlorophyll concentration, while a few algal symbiont‐bearing species occur in greatest abundance in the mixed layer. The δ18O measurements of planktonic foraminifera shells from core top sediment samples confirm the vertical stratification within the photic zone that is suggested by the relationship between hydrography and abundances found in the plankton tows and found in the statistical study by Ravelo et al. [1990]. Comparison between the measured δ18O values of planktonic foraminifera with the predicted δ18O profiles of the overlying water column at three core locations indicate that species abundances in the sediment record the seasonally integrated conditions of the photic zone and suggests that the abundance of a species in the sediment depends on whether the preferred ecological conditions of that species may be found within the photic zone of the overlying water column sometime during the year. Species which calcify below the photic zone have only trace relative abundances. Finally, it appears that the total range of δ18O values of the dominant species approximates the predicted annual δ18O of calcite range in the upper 80 m of the water column.
Patterns of Ice‐Rafted Detritus in the Glacial North Atlantic (40–55°N)
Authors: Grousset F. E. , Labeyrie L. , Sinko J. A. , Cremer M. , Bond G. , Duprat J. , Cortijo E. , Huon S.
Published: February 2008

The observation by Heinrich (1988) that, during the last glacial period, much of the input of ice‐rafted detritus to the North Atlantic sediments may have occurred as a succession of catastrophic events, rekindled interest on the history of the northern ice sheets over the last glacial period. In this paper, we present a rapid method to study the distribution of these events (both in space and time) using whole core low‐field magnetic susceptibility. We report on approximately 20 cores covering the last 150 to 250 kyr. Well‐defined patterns of ice‐rafted detritus appear during periods of large continental ice‐sheet extent, although these are not always associated within their maxima. Most of the events may be traced across the North Atlantic Ocean. For the six most recent Heinrich layers (HL), two distinct patterns exist: HL1, HL2, HL4, HL5 are distributed along the northern boundary of the Glacial Polar Front, over most of the North Atlantic between ≈40° and 50°N; HL3 is more restricted to the central and eastern part of the northern Atlantic. The Nd‐Sr isotopic composition of the material constituting different Heinrich events indicates the different provenance of the two patterns: HL3 has a typical Scandinavia‐Arctic‐Icelandic “young crust” signature, and the others have a large component of northern Quebec and northern West Greenland “old crust” material. These isotopic results, obtained on core SU‐9008 from the North American basin, are in agreement with the study by Jantschik and Huon (1992), who used K‐Ar dating of silt‐ and clay‐size fractions of an eastern basin core (ME‐68‐89). These data confirm the large spatial scale of these events, and the enormous amount of ice‐rafted detritus they represent.
Radon transport from soil to air
Authors: Nazaroff William W.
Published: February 2008

Radon generated within the upper few meters of the Earth's crust by the radioactive decay of radium can migrate during its brief lifetime from soil into the atmosphere. This phenomenon leads to a human health concern as inhalation of the short‐lived decay products of radon causes irradiation of cells lining the respiratory tract. This paper reviews the factors that control the rate at which two radon isotopes, 222Rn and 220Rn, enter outdoor and indoor air from soil. The radium content of surface soils in the United States is usually in the range 10–100 Bq kg−1. The emanation coefficient, which refers to the fraction of radon generated in a material that enters the pore fluids, varies over a wide range with a typical value being 0.2. Radon in soil pores may be partitioned among three states: in the pore air, dissolved in the pore water, and sorbed to the soil grains. Except in the immediate vicinity of buildings, radon migrates through soil pores principally by molecular diffusion. Average reported flux densities from undisturbed soil into the atmosphere are 0.015–0.048 Bq m−2 s−1 for 222Rn and 1.6–1.7 Bq m−2 s−1 for 220Rn. Soil is the dominant source of radon in most buildings. Advective flow of soil gas across substructure penetrations is a key element in the transport process. The advective flow is driven by the weather (wind and indoor‐outdoor temperature differences) and by the operation of building systems, such as heating and air conditioning equipment. A typical radon entry rate into a single‐family dwelling of 10–15 kBq h−1 can be accounted for by weather‐induced pressure‐driven flow through moderately to highly permeable soils. The extent to which diffusion through soil pores contributes to radon entry into buildings is not known, but in buildings with elevated concentrations, diffusion is believed to be less important than advection.
Fluids in accretionary prisms
Authors: Moore J. Casey , Vrolijk Peter
Published: February 2008

Accretionary prisms are composed of initially saturated sediments caught in subduction zone tectonism. As sediments deform, fluid pressures rise and fluid is expelled, resembling a saturated sponge being tectonically squeezed. Fluid flow from the accretionary prism feeds surface biological cases, precipitates and dissolves minerals, and causes temperature and geochemical anomalies. Structural and metamorphic features are affected at all scales by fluid pressures or fluid flow in accretionary prisms. Accordingly, this dynamic tectonic environment provides an accessible model for fluid/rock interactions occurring at greater crustal depths. Porosity reduction and to a lesser degree mineral dehydration and the breakdown of sedimentary organic matter provide the fluids expelled from accretionary prisms. Mature hydrocarbons expulsed along prism faults indicate deep sources and many tens of kilometers of lateral transport of fluids. Many faults cutting accretionary prisms expel fluids fresher than seawater, presumably generated by dehydration of clay minerals at depth. Models of fluid flow from accretionary prisms use Darcy's law with matrix and fractures/faults being assigned different permeabilities. Fluid pressures in accretionary prisms are commonly high but range from hydrostatic to lithostatic. Matrix or intergranular permeability ranges from less than 10−20 m² to 10−13 m². Fracture permeability probably exceeds 10−12 m². A global estimate of fluid flux into accretionary prisms suggests they recycle the oceans every 500 m.y. Fluid flow out of accretionary prisms occurs by distributed flow through intergranular permeability and along zones of focused flow, typically faults. Focused fluid flow is 3 to 4 orders of magnitude faster than distributed flow, probably representing the mean differences in permeability along these respective expulsion paths. During the geological evolution of accretionary prisms, distributed flow through pore spaces decreases as a result of consolidation and cementation, whereas flow along fracture systems becomes dominant. Although thrust faults are most common in the compressional environment of accretionary prisms, normal and strike‐slip faults are efficient fluid drains, because they are easier to dilate. Observations from both modern and ancient prisms suggest episodic fluid flow which is probably coupled to episodic fault displacement and ultimately to the earthquake cycle.
Toward an optimum receiving array and pulse set for the Dynasonde
Authors: Pitteway M. L. V. , Wright J. W.
Published: February 2008

The accuracy and efficiency with which radio echo parameters may be estimated by a programmable ionosonde of high resolution depend upon software‐designed strategies of pulse set design and receiving antenna layout. All of the echo parameters, except amplitude and time of arrival (thus three components of echolocation, Doppler, polarization rotation, and an average phase angle) are determined by phase angle differences. The solution is conveniently expressed as a least squares estimation, provided that more than six independent phase measurements are available. Since the observed phases are necessarily obtained modulo 360°, from 12‐bit complex amplitude data, each parameter is subject to aliasing ambiguities which must be anticipated in each strategy, and minimized.
On magnetotelluric source effects caused by an auroral electrojet system
Authors: Pirjola Risto
Published: February 2008

A sophisticated theoretical model of the auroral electrojet current system is applied to estimate the source effect distortion in magnetotelluric apparent resistivity values at auroral latitudes. Clear differences from the correct Cagniard plane wave value can occur at periods larger than about 1 min. It is further indicated that changing values of the parameters included in the electrojet model may essentially affect the source effect distortion, which complicates an estimation of the distortion. Thus it is very difficult to extract information about the Earth's conductivity structure from magnetotelluric measurements influenced by electrojet currents. In order not to overestimate the source effects, models in which the electromagnetic field, which is produced by an electrojet system, is superposed on a background field are also discussed. As expected, the source effect distortion then becomes clearly smaller in the apparent resistivity, but it does not vanish.
Diffraction of nonaxisymmetric waves in cylindrically layered media by horizontal discontinuities
Authors: Liu Qing‐Huo , Chew Weng Cho
Published: February 2008

In this paper a numerically efficient algorithm is developed for solving the problem of nonaxisymmetric wave propagation in cylindrically layered media with horizontal discontinuities. For an off‐axis source in cylindrically layered media, because the nonaxisymmetry of the waves gives rise to the vectorial coupling between TE and TM waves, the modeling of the wave propagation becomes much more difficult than for a centered (axisymmetric) source. However, the numerical mode‐matching method proposed here calculates very efficiently the electromagnetic fields in cylindrically layered media with horizontal discontinuities. Several numerical examples are given to verify the numerical method and to illustrate the applications of this method in the calculation of the field generated by a magnetic dipole source.
Longitudinal propagation of low‐frequency waves in a switched magnetoplasma medium
Authors: Madala Sudhakar Rao V. , Kalluri Dikshitulu K.
Published: February 2008

The interaction of electromagnetic radiation with a time‐switched magnetoplasma is considered. Exact analysis, including ion motion, for longitudinal propagation is given. The original wave splits into four new waves whose frequencies are different from the incident wave frequency. Approximate dispersion relations are obtained in the Alfvén and hydromagnetic ranges. The energy distribution, power content, and frequency shifts in each of the four new waves are discussed in these low‐frequency regions. It is shown that the low‐frequency waves degenerate into dc wiggler magnetic fields for the limiting case of switching an isotropic plasma medium. Parameters and typical values for an experiment that will illustrate the generation of the new waves are given.
Performance analysis of a multifrequency radiometer for predicting atmospheric propagation parameters
Authors: Schiavon G. , Solimini D. , Westwater E. R.
Published: February 2008

This study concerns the predicted performance of multifrequency ground‐based radiometers in estimating atmospheric moisture and the corresponding attenuation and wet path delay on an Earth‐space path. The analysis of the performance is based on a numerical simulation using possible combinations of radiometric channels at 10 microwave frequencies below 100 GHz. We first discuss the accuracy of retrievals of both integrated atmospheric vapor and cloud liquid from noisy radiometric measurements carried out at two frequencies and investigate the improvement attainable by using more than two radiometric channels. Then we focus on the problem of predicting attenuation and wet path delay at several frequencies in the millimeter wave range for a vertical Earth‐space path from radiometric data. Examples of possible combinations of two and three frequencies are presented, ranked according to their capability, first in retrieving vapor and liquid, then in predicting attenuation and wet path delay for two different climatologies.
Thermal and barometric constraints on the intrusive and unroofing history of the Black Mountains: Implications for timing, initial dip, and kinematics of detachment faulting in the Death Valley Region, California
Authors: Holm Daniel K. , Snow J. Kent , Lux Daniel R.
Published: February 2008

Unroofing of the Black Mountains, Death Valley, California, has resulted in the exposure of 1.7 Ga crystalline basement, late Precambrian amphibolite facies metasedimentary rocks, and a Tertiary magmatic complex. The 40Ar/39Ar cooling ages, obtained from samples collected across the entire length of the range (>55 km), combined with geobarometric results from synextensional intrusions, provide time‐depth constraints on the Miocene intrusive history and extensional unroofing of the Black Mountains. Data from the southeastern Black Mountains and adjacent Greenwater Range suggest unroofing from shallow depths between 9 and 10 Ma. To the northwest in the crystalline core of the range, biotite plateau ages from ∼13 to 6.8 Ma from rocks making up the Death Valley turtlebacks indicate a midcrustal residence (with temperatures >300°C) prior to extensional unroofing. Biotite 40Ar/39Ar ages from both Precambrian basement and Tertiary plutons reveal a diachronous cooling pattern of decreasing ages toward the northwest, subparallel to the regional extension direction. Diachronous cooling was accompanied by dike intrusion which also decreases in age toward the northwest. The cooling age pattern and geobarometric constraints in crystalline rocks of the Black Mountains suggest denudation of 10–15 km along a northwest directed detachment system, consistent with regional reconstructions of Tertiary extension and with unroofing of a northwest deepening crustal section. Mica cooling ages that deviate from the northwest younging trend are consistent with northwestward transport of rocks initially at shallower crustal levels onto deeper levels along splays of the detachment. The well‐known Amargosa chaos and perhaps the Badwater turtleback are examples of this “splaying” process.

Considering the current distance of the structurally deepest samples away from moderately to steeply east tilted Tertiary strata in the southeastern Black Mountains, these data indicate an average initial dip of the detachment system of the order of 20°, similar to that determined for detachment faults in west central Arizona and southeastern California. Beginning with an initially listric geometry, a pattern of footwall unroofing accompanied by dike intrusion progresses northwestward. This pattern may be explained by a model where migration of footwall flexures occur below a scoop‐shaped hanging wall block. One consequence of this model is that gently dipping ductile fabrics developed in the middle crust steepen in the upper crust during unloading. This process resolves the low initial dips obtained here with mapping which suggests transport of the upper plate on moderately to steeply dipping surfaces in the middle and upper crust.
Paleomagnetism of Late Paleozoic rocks in the Tianshan, northwestern China
Authors: Nie Shangyou , Rowley David B. , Van der Voo Rob , Li Maosong
Published: February 2008

A paleomagnetic study of late Paleozoic rocks in two areas of northwestern China helps to constrain the timing of collision between Tarim and the Junggar part of Eurasia along Tianshan. A primary Late Permian direction (D/I = 198/−59, K=24, A95=12.6) is derived from seven sites (53 samples) from the Heavenly Lake (Tianzhi) section in northern Tianshan that has both normal and reversed polarities and passes a fold test at the 99% confidence level. This result gives a latitude of 39°N in the Late Permian for southern Junggar. Twenty‐two sites (144 samples) from the Devonian and Carboniferous rocks across Tianshan reveal postfolding remagnetizations some of which are interpreted as being acquired in the Permian due to the Tarim‐Eurasia collision. The Late Permian paleomagnetic pole from the Heavenly Lake section is statistically indistinguishable from three published Late Permian poles from Tarim indicating closure of the Tianshan ocean and suturing of Tarim and Junggar before that time. These paleomagnetic poles from northwestern China are, however, significantly different from those of stable Eurasia, suggesting substantial later relative motion that can be partly accounted for by the progressive closure of the Mongolo‐Okhotsk ocean and associated tectonic rotations. The absence of a discernable Permian ocean record west of the Khangay highland in central Mongolia requires that the rotations be accommodated within a diffusive plate boundary in the Eurasian continent. A Late Permian continental plate reconstruction is presented that takes into consideration these new paleomagnetic results and other geological constraints.
Pleistocene strike‐slip tectonics in the Lucanian Apennine (southern Italy)
Authors: Catalano Stefano , Monaco Carmelo , Tortorici Luigi , Tansi Carlo
Published: February 2008

Structural studies carried out in the Lucanian Apennines (Southern Italy) show that strike‐slip faulting was the principal mode of deformation of this area during middle‐upper Pleistocene time. W‐NW to E‐SE trending left strike‐slip fault systems dissect the entire Apennine mountain belt and affect the preexisting thrust geometry. Strike‐slip faults, activated by a roughly E‐W shortening, are characterized by different geometries representing the surface response to lateral motion occurring along deep‐seated structures. The occurrence of different structural patterns which characterize different segments of strike‐slip system is related to (1) the depth of a major decoupling surface which separates the upper tectonic multilayered horizon (Apennines thrust belt system) from the lower rigid horizon (Apulian belt) in which strike‐slip structures have originated and (2) the geometric relationships between the strike‐slip faults and the thrust belt pattern which characterize the upper horizon. The different segments of the strike‐slip system are interpreted as internal deformation developed within a crustal shear zone. This zone, which corresponds to the boundary between the Apulian block and the Apennine chain, is characterized by sinistral movement as a response to the northwesterly convergent motion of the African plate with respect to Europe.
Oceanic 13C/12C observations: A new window on ocean CO2 uptake
Authors: Tans Pieter P. , Berry Joseph A. , Keeling Ralph F.
Published: February 2008

Equations are developed describing the rate of change of carbon isotopic ratios in the atmosphere and oceans in terms of δ13C quantities. The equations enable one to perform calculations directly with δ and ϵ quantities commonly reported in the literature. The main cause of the change occurring today is the combustion of fossil fuel carbon with lower δ13C values. The course of this isotopic anomaly in atmosphere and oceans can provide new constraints on the carbon budgets of these reservoirs. Recently published δ13C isotopic data of total inorganic carbon in the oceans [Quay et al., 1992] appear to lead to incompatible results with respect to the uptake of fossil fuel CO2 by the oceans if two different approaches to the data are taken. Consideration of the air‐sea isotopic disequilibrium leads to an uptake estimate of only a few tenths of a gigaton C (Gt, for 1015 g) per year, whereas the apparent change in the ocean δ13C inventory leads to an estimate of more than 2 Gt C yr−1. Both results are very uncertain with presently available data. The isotopic ratio has the advantage that the signal‐to‐noise ratio for the measurement of the uptake of the isotopic signal by the oceans is better than for the uptake of total carbon, The drawback is that isotopic exchange with carbon reservoirs that are difficult to characterize introduces uncertainty into the isotopic budget. The accuracy requirements for the measurements are high, demanding careful standardization at all stages.
Tree growth in carbon dioxide enriched air and its implications for global carbon cycling and maximum levels of atmospheric CO2
Authors: Idso Sherwood B. , Kimball Bruce A.
Published: February 2008

In the longest carbon dioxide enrichment experiment ever conducted, well‐watered and adequately fertilized sour orange tree seedlings were planted directly into the ground at Phoenix, Arizona, in July 1987 and continuously exposed, from mid‐November of that year, to either ambient air or air enriched with an extra 300 ppmv of CO2in clear‐plastic‐wall open‐top enclosures. Only 18 months later, the CO2‐enriched trees had grown 2.8 times larger than the ambient‐treated trees; and they have maintained that productivity differential to the present day. This tremendous growth advantage is due to two major factors: a CO2‐induced increase in daytime net photosynthesis and a CO2‐induced reduction in nighttime dark respiration. Measurements of these physiological processes in another experiment have shown three Australlian tree species to respond similarly; while an independent study of the atmosphere's seasonal CO2cycle suggests that all earth's trees, in the mean, probably share this same response. A brief review of the plant science literature outlines how such a large growth response to atmospheric CO2enrichment might possibly be maintained in light of resource limitations existing in nature. Finally, it is noted that a CO2“fertilization effect” of this magnitude should substantially slow the rate at which anthropogenic carbon dioxide would otherwise accumulate in the atmosphere, possibly putting an acceptable upper limit on the level to which the CO2content of the air may ultimately rise.
A biogeochemical study of the coccolithophore, Emiliania huxleyi, in the North Atlantic
Authors: Holligan Patrick M. , Fernández Emilio , Aiken James , Balch William M. , Boyd Philip , Burkill Peter H. , Finch Miles , Groom Stephen B. , Malin Gillian , Muller Kerstin , Purdie Duncan A. , Robinson Carol , Trees Charles C. , Turner Suzanne M. , van der Wal Paul
Published: February 2008

The biogeochemical properties of an extensive bloom (∼250,000 km2) of the coccolithophore, Emiliania huxleyi, in the north east Atlantic Ocean were investigated in June 1991. Satellite (NOAA‐AVHRR) imagery showed that the bloom was centered initially at 60°–63°N by 13°–28°W and lasted approximately 3 weeks. Spatial variations in satellite‐measured reflectance were well correlated with surface measurements of the beam attenuation coefficient, levels of particulate inorganic carbon, and coccolith density. Rates of both photosynthesis and calcification were typically relatively low within the coccolithophore‐rich waters, suggesting the population was in a late stage of development at the time of the field observations. Levels of dimethyl sulphide (DMS) in surface waters were high compared to average ocean values, with the greatest concentrations in localized areas characterized by relatively high rates of photosynthesis, calcification, and grazing by microzooplankton. The estimated spatially averaged flux of DMS to the atmosphere was 1122 nmol m−2 h−1, somewhat greater than that determined for the same region in June‐July 1987. Coccolith production (1 × 106 tonnes calcite‐C) had a significant impact on the state of the CO2 system, causing relative increases of up to 50 μatm in surface pCO2 in association with alkalinity and water temperature changes. Gradients in pCO2 were as great as 100 μatm over horizontal distances of 20–40 km. The environmental implications of these findings are discussed in relation to the spatial and temporal distributions of E. huxleyi.
Influence of horizontal inhomogeneity in the ionosphere on the reflection of Alfvén waves
Authors: Zhu L. , Sojka J. J. , Schunk R. W. , Crain D. J.
Published: February 2008

A study of the reflection of Alfvén waves at a horizontally inhomogeneous ionosphere has been carried out. In this study, the Alfvén speed above the ionosphere is assumed to be uniform and the ionosphere is treated as a height‐integrated conducting slab. Analytical and numerical results indicate that the horizontal nonuniformity of the ionospheric conductivity can lead to a rotation of the reflected wave fields and cause field‐aligned currents that originate in the ionosphere. A strong conductivity nonuniformity in the direction perpendicular to the incident wave field, large Hall to Pedersen conductivity ratios, and low conductivity values lead to a large rotation of the reflected wave field in the range from a few to 40°. The implications of the theoretical results for some ionospheric phenomena are presented, including comments on the Harang discontinuity and Sun‐aligned arcs.
auroral electron transport using the Monte Carlo Method
Authors: Solomon Stanley C.
Published: February 2008

A new algorithm for calculation of energetic electron fluxes in the atmosphere is described. Results are compared with other methods and the implications for auroral spectroscopic analysis are discussed. Good agreement is obtained with the model of Strickland et al. [1976, 1989].
Local network observation of the Earth's free oscillations: Apparent centroid of the 1989 MacQuarie Ridge Earthquake
Authors: Hori Sadaki , Fukao Yoshio , Suda Naoki , Ishihara Yasushi , Shibutani Takuro , Hirahara Kazuro
Published: February 2008

A local broadband seismograph network in Honshu Island, Japan, recorded the free oscillations excited by the 1989 Macquarie Ridge earthquake, one of the largest strike‐slip events in the last decade. The initial amplitude pattern of the spheroidal modes varies from station to station in the network in spite of the small differences in epicentral distance and epicenter‐to‐station azimuth. Theoretical amplitude of each mode depends on the earthquake mechanism and distance. The most dramatic change occurs for a pure strike‐slip event near the distance of 90° where the initial amplitude of every odd order multiplet becomes exactly zero. This is the case for the Macquarie Ridge earthquake observed in Japan. From this sensitivity of the amplitude pattern to the epicentral distance, we can estimate the apparent centroid location by searching a minimum misfit between the observed and theoretical initial amplitudes. The apparent centroid, which is a projection of the real centroid onto the great circle path, is estimated to be 49 km from the epicenter in an azimuth of N19°W.
Phobos events as precursors of solar wind‐Dust interaction
Authors: Sauer Konrad , Baumgärtel Klaus , Motschmann Uwe
Published: February 2008

Significant magnetic field perturbations in the solar wind were observed during the Phobos‐2 elliptical orbits around Mars when the spacecraft crossed the Phobos orbit. As remarkable feature, these so‐called Phobos events were detected in all cases only on the upstream side of the Phobos orbit. A simple one‐dimensional fluid model is developed which shows that a thin charged dust cloud with an extension of no more than 100 km is able to produce phase‐standing, right‐hand polarized precursor waves with a spatial periodicity of about the proton skin length. This is the same type of upstream waves which is generated by oblique, subcritical shocks. The measured period of the magnetic variations (≈40 s) may be explained as Doppler shift owing to the spacecraft motion through the standing wave structure. The fluid results are confirmed by hybrid code simulations. In conclusion, we suggest the Phobos events to be precursor waves resulting from the interaction of the solar wind with charged dust rings along the Phobos orbit.
Fast Three dimensional driven reconnection
Authors: Strauss H. R.
Published: February 2008

Fast driven reconnection in a three dimensional axially bounded flux tube is studied in numerical simulations and in a simple analytic model. Numerical examples are given in which the reconnection time is a very weak function of resistivity η. The data is consistent with a reconnection time scaling as | log η |. A simple analytic model agrees with many features of the computational data.
Reconstruction of low‐dimensional magnetospheric dynamics by singular spectrum analysis
Authors: Sharma A. S. , Vassiliadis D. , Papadopoulos K.
Published: February 2008

The low dimensionality of magnetospheric activity indicated by previous phase space reconstructions using the AE and AL data suffer from the limitations of these techniques. In this paper the singular spectrum analysis is used to study the global magnetospheric dynamics using the AE data and it yields a correlation dimension ≃2.5, thus confirming the low dimensionality published earlier. Further, this technique shows that the global magnetospheric dynamics can be described by 3 variables whose dynamical features are obtained from the AE data.
Effect of competitive adsorption on polar stratospheric cloud reactions
Authors: Mozurkewich Michael
Published: February 2008

Existing laboratory data for reaction rates on ice and nitric acid trihydrate are interpreted in terms of a simple, speculative mechanism for these reactions. The mechanism assumes that the solid phase is either pure H2O or pure HNO3(H2O)3 and that the state of the surface depends largely on the gas phase composition. This dependence is described by Langmuir adsorption isotherms. The adsorption of a nonreactive species can affect the rate of reaction by inhibiting the adsorption of reactive species. In particular, differences in reaction rates observed on ice and HNO3(H2O)3 are attributed to the adsorption of gas phase HNO3 produced by the decomposition of HNO3(H2O)3. The interpretation of heterogeneous reaction rates requires detailed measurements of the rates as a function of gas phase composition.
Thermal expansion of mantle and core materials at very high pressures
Authors: Duffy Thomas S. , Ahrens Thomas J.
Published: February 2008

The thermal expansivities (α) of MgO and high‐pressure phases of CaO, CaMgSi2O6, and Fe at ultrahigh pressure are obtained by comparing existing shock compression and temperature measurements to 300 K compression curves constructed from ultrasonic elasticity and static compression data. For MgO, α can be represented by: α = ρoγoCV(ρo/ρ)0.5±0.5/KT where γ is the Grüneisen parameter, CV is the constant volume specific heat, KT is the isothermal bulk modulus, and ρ is the density. Using this expression, the thermal expansivity of MgO is 28‐32×10−6K−1 at the pressure of the top of the lower mantle and 10‐16×10−6K−1 at its base (at 2000 K). New data for α of ε‐Fe, together with an inner core temperature of 6750 K, constrain the density of the inner core to be 5±2% less than the density of ε‐Fe, implying the inner core contains a light element.