bluuebunny/crossref_metadata_2025 huggingface dataset:
Crustal structure in eastern Kazakh, U.S.S.R. from teleseismic receiver functions
Authors: Priestley Keith F. , Zandt George , Randall George E.
Published: February 2008

Broadband receiver functions determined from teleseismic P‐waveforms recorded at two seismic stations in eastern Kazakh, U.S.S.R., are inverted for the vertical velocity structure beneath the stations. The detailed broadband receiver functions are obtained by stacking source‐equalized radial components of teleseismic P‐waveforms. A time‐domain inversion of the radial receiver function is used to determine the structure assuming a crustal model parameterized by flat‐lying, homogeneous layers. The general features of the inversion results are: a complex shallow crust, velocities less than 6 km/s in the upper crust, a high velocity (6.9‐7.5 km/s) lower crust, and a Moho that varies between 47 and 57 km depth. These results compare favorably with a composite velocity model from Deep Seismic Sounding data, but show lower velocities in the upper crust, and higher velocities in the lower crust. The results indicate that the crust in this region is relatively uniform, however the nature and depth of the Moho changes significantly across the region. The receiver function inversion structure for the Kazakh sites is similar to a published receiver function structure for a site on the Canadian Shield.
Spectral discrimination of NTS explosions and earthquakes in the southwestern United States using high‐frequency regional data
Authors: Chael Eric P.
Published: February 2008

A high‐frequency seismic station has been operating since March, 1987, near Nelson, NV. Records of earthquakes at regional distances from the station show substantially more energy at frequencies above 10 Hz than records of nuclear tests of comparable magnitude on the Nevada Test Site. This contradicts the predictions made by investigators who have advocated high‐frequency monitoring for nuclear test detection and identification. Measuring the slopes of the Pg velocity spectra between 4 and 30 Hz successfully discriminates 11 NTS explosions from 36 earthquakes recorded in the first seven months of operation. The spectral differences may result from the respective source depths, with the earthquakes occurring deeper and in faster material than the explosions.
A clockwise rotation of southern Apulia?
Authors: Tozzi M. , Kissel C. , Funiciello R. , Laj C. , Parotto M.
Published: February 2008

New paleomagnetic results from 13 sites sampled in Eo‐Oligocene autochthonous formations in the extreme South of the Apulian platform in southeastern Italy are presented. They suggest that this region has undergone a clockwise rotation of about 25° since the Eo‐Oligocene. This rotation is opposite in sense to that obtained from the Cretaceous formations in the Gargano, which has generally been assumed to affect the entire foreland. These new data suggest that the Tertiary structural evolution of this region may be distinct from that of central peninsular Italy and related to that of northwestern Greece on the other side of the Southern Adriatic Sea.
Constraints on the neutral hydrogen corona at Uranus from its interaction with magnetospheric plasma
Authors: Herbert Floyd
Published: February 2008

Models of collisional reactions between the hot (several keV) protons and neutral atomic hydrogen corona observed at Uranus by Voyager 2 are compared with the observations in order to deduce constraints on the coronal density. An upper limit is found for nH(5RU) of several tens of H/cm³ on the sunward side of Uranus and several H/cm³ on the dark side. The possibility that the hot plasma population might arise from photoionization and electron impact ionization of coronal and interstellar medium hydrogen in the magnetotail, followed by pickup and energization while convecting toward Uranus, is examined and rejected.
Studies of the electrical charging of the tethered electron accelerator mother‐daughter pocket Maimik
Authors: Maehlum B. N. , Troim J. , Maynard N. C. , Denig W. F. , Friedrich M. , Torkar K. M.
Published: February 2008

The MAIMIK experiment was designed to study the charging of an electron‐beam emitting payload using a tethered mother‐daughter payload configuration. The particle accelerator on the daughter emitted short pulses of 8 keV energy electrons with a beam current which was varied in 6 steps from 20 to 800 mA. During the highest beam currents the accelerator payload was charged to potentials more than 50 per cent greater than the beam energy. It is speculated that a combination of a low background plasma density and a small payload may account for the apparently anomalous result.
Evidence for periodic reconnection at Uranus?
Authors: Richardson J. D. , Belcher J. W. , Selesnick R. S. , Zhang M. , Siscoe G. L. , Eviatar A.
Published: February 2008

The unique orientation of Uranus at the time of the Voyager 2 encounter results in a convection dominated magnetosphere. Plasma and magnetic field data from the tail magnetosheath are presented. Velocity decreases of 5‐10% seem to occur with a 17 hour period. At least four repetitions of this decrease are observed, in all cases when flow passes over the dayside polar cap. One possible interpretation of these features is that they are signatures of dayside reconnection. The cause of the velocity decreases would be drag on the reconnected flux tubes which are coupled via Birkeland currents to the ionosphere. The coupling efficiency for power transfer between the solar wind and Uranian magnetosphere implied by these decreases is consistent with previous determinations of this quantity.
ISEE 1 & 2 observations of the oscillating magnetopause
Authors: Song Pu , Elphic R. C. , Russell C. T.
Published: February 2008

Examination of multiple magnetopause crossings observed with the magnetometers on ISEE 1 and 2 has allowed us to determine the amplitude of the oscillation of surface waves on the magnetopause with periods greater than about 2 minutes and its dependence on latitude, local time and direction of the interplanetary magnetic field (IMF). The magnetopause is more oscillatory for southward IMF than for northward IMF. When the IMF is southward, the amplitude of the oscillation increases with increasing angle from the subsolar point, which suggests that reconnection‐related phenomena can generate surface waves on the magnetopause. When the IMF is northward, the oscillation does not grow with distance from the subsolar point, which is contrary to the expected growth of the Kelvin‐Helmholtz (K‐H) instability. A study of the spectrum of the solar wind dynamic pressure shows that solar wind pressure fluctuations may cause all of the observed boundary oscillations for northward IMF. Thus the K‐H instability plays at most a very minor role in causing the surface waves on the dayside magnetopause with periods longer than about 2 minutes.
Nonlinear 3‐D evolution of bounded kinetic Alfven waves due to shear flow and collisionless tearing instability
Authors: Seyler Charles E.
Published: February 2008

The three‐dimensional nonlinear simulation of the evolution of a kinetic Alfven wave is presented for simple boundary conditions that resemble those of a discrete auroral breakup arc. The model used is a variant of the reduced magnetohydrodynamic description that includes, in addition, the important dispersive effect of electron inertia. It is found that with a "generator" boundary condition corresponding to a current generator and a fully conducting "load" boundary, the wave evolves three dimensionally through a combination of shear flow and collisionless tearing mode instability.
ClO and O3 stratospheric profiles: Balloon microwave measurements
Authors: Waters J. W. , Stachnik R. A. , Hardy J. C. , Jarnot R. F.
Published: February 2008

Stratospheric ClO and O3 vertical profiles were measured at 32° N in May 1985 and October 1986. The ClO profiles and diurnal variation are in general agreement with theory, but have somewhat less midday ClO near 34 km. Measured 35‐45 km O3 is larger than theory and no stratospheric O3 diurnal variation was observed, as expected. HNO3 was detected, and an H2O2 upper limit obtained.
Geodetic evidence of the seismic potential at Parkfield, California
Authors: Sung Li‐yu , Jackson David D.
Published: February 2008

We use observed line length change rates and shallow fault slip rates at Parkfield, California to estimate the slip rate at depth on the San Andreas fault. One model featuring a nearly monotonic transition from creeping behavior on the northwest to locked behavior on the southeast fits the data acceptably well. An isolated asperity fits the data better, but not significantly. Evidence for the asperity comes from two lines connecting stations where mildly inconsistent data have been collected. Thus evidence for the asperity is marginal. Stored elastic energy southeast of Parkfield could produce an earthquake of magnitude up to 8.0 that would have displacement and rupture length similar to historic earthquakes of the same size. Smaller events are of course more likely, but the geodetic data do not favor a "characteristic" M=6 event.
500 mb winter variability over the Antarctic (Palmer) Peninsula
Authors: Nogues‐Paegle Julia , Stucki Susan C.
Published: February 2008

Winter time variability of heights over the Antarctic peninsula, Weddell Sea and Queen Maud Land are shown to have important contributions from correlations between the zonally averaged height field ([Z]) and longitudinally asymmetric motions. This is different from what it is observed at other longitudes, where the time variance can be explained in terms of variance of the zonally averaged fields plus the variance of deviations from zonal averages. It is shown that when [Z] is larger than its winter average a pattern with southerlies over the Weddell Sea at 500 mb and northerlies over eastern Antarctica develops south of 60°S. These southerlies are found displaced about 15° northward with episodes of meridional wind magnitudes over eastern Antarctica larger than 2 m/s. The equivalent barotropic structure of Southern Hemisphere tropospheric long waves justify extension of the 500 mb results presented here to higher levels. Recent measurements taken by the Airborne Antarctic Ozone Experiment in the upper troposphere and lower stratosphere (10 to 18 km above sea level) have detected the presence of ozone depleted air over the Antarctic Peninsula and Weddell Sea. It is conjectured here, that this may be partly due to the transport of ozone poor air from high‐latitudes into this region.
Geologic structure near the Cajon Pass Scientific Drill Hole
Authors: Ehlig Perry L.
Published: February 2008

The geologic structure near the Cajon Pass drill site is controversial. The Squaw Peak fault was previously interpreted as the edge of a thrust plate of large displacement. This may be incorrect based on the style of deformation and the presence of similar granodiorite on both sides of the fault. Alternatively, mid‐Miocene crustal extension on a west‐facing listric normal fault may have formed the basin in which the Cajon Formation was deposited. Post Miocene crustal shortening normal to the San Andreas fault may have folded the upper plate of this fault and thrust it northeastward. By this interpretation, steeply inclined beds at the drill site terminate on a fault ramp, and Squaw Peak is the corner of the initially stable block that was broken off and ramped upward.
Implications of zeolites and their zonation in the Cajon Pass Deep Drillhole
Authors: James Eric W. , Silver Leon T.
Published: February 2008

Zeolites occur in all cores and most cuttings samples of plutonic and gneissic rock from the Cajon Pass Deep Drillhole. Laumontite or stilbite replace plagioclase and fill fractures <1 mm to several cms in width. Zeolitic alteration is most intense in faulted and fractured zones. Zeolite species are zoned vertically. Laumontite occurs to a depth of 1885 m, stilbite from 1885 m to 2080 m and laumontite again to at least 2524 m. The transition from stilbite to laumontite at 2080 m fits both extrapolated equilibria and the CPDDH P‐T gradient but laumontite occurrences above 1885 m are metastable apparently reflecting rapid uplift. Radioactive accessory minerals from the wall rock surrounded by zeolites in some fractures exhibit red‐brown haloes. Halo intensity correlates to mineral radioactivity and may allow dating of mineraliztion. Observation in the CPDDH suggest a potential role for zeolites in determining chemical and physical properties such as pore water composition, seismic velocity, and gravity contrasts in faults of the San Andreas system.
The stress heat‐flow paradox and thermal results from Cajon Pass
Authors: Lachenbruch Arthur H. , Sass John H.
Published: February 2008

Conventional friction models predict a substantial thermal anomaly associated with active traces of strike‐slip faults, but no such anomaly is observed from over 100 heat‐flow determinations along 1,000 km of the San Andreas fault. The Cajon Pass well is being drilled to bring deep heat‐flow and stress data to bear on this paradox. Preliminary heat flows to 1.7 km in the neighboring Arkoma well indicated a positive anomaly of about 30% as would be expected if frictional resistance of the fault were 50 MPa or so, but the Pliocene and Pleistocene history of the Transverse Ranges, particularly high rates of uplift and erosion, could also explain the anomaly. Preliminary stress results from Cajon Pass and a new interpretation of regional data by Mark D. Zoback and colleagues suggests that the maximum compressive stress near the fault is almost normal to the trace, and hence the resolved shear stress is low and the fault, weak. Although this is consistent with long‐standing evidence from low heat flow, vexing questions remain regarding the physics of strike‐slip faulting. The heat‐flow data show large variability with depth, probably from three‐dimensional structure, and an overall decrease from over 90 mW/m² in the upper kilometer to less than 80 mW/m² in the lower 300 m with no evidence of advective heat transfer. Whether this decreasing trend is significant and whether it continues downward to the background value (∼70 mW/m² less the radiogenic heat from overlying rocks) as expected for a weak fault must be verified with data from greater depth.
Borehole electrical images in the basement of the Cajon Pass Scientific Drillhole, California; Fracture identification and tectonic implications
Authors: Pezard Philippe A. , Luthi Stefan M.
Published: February 2008

Borehole electrical images were recorded in the upper crystalline basement of the Cajon Pass scientific drillhole as part of an extensive program of downhole experiments. In spite of the large borehole size and the high resistivity of basement rocks, excellent images were obtained from 850 m to 1820 m. Such oriented electrical images resolve the texture of igneous rocks, and provide a means of identifying and mapping open or mineralized fractures. In order to study more precisely the response of the images to basement features, they were compared to sections where cores had been recovered. The images are in good agreement with the cores, thereby permitting their orientation. In all, over 800 fractures were mapped from 850 to 1820 m on the images. Whereas the foliations have generally low dips, the fractures are often steep. Most of the fractures strike NE‐SW to E‐W, in a direction orthogonal to the trace of the San Andreas Fault. This is consistent with the results of Zoback et al. [1987], hydraulic fracturing experiments at Cajon Pass [Zoback and Healy, this issue], and the analysis of borehole breakouts at Cajon Pass [Shamir et al., this issue]. The analysis of the electrical images suggests that the observed present‐day stress regime in the vicinity of the San Andreas Fault might have remained constant over the past few million years.
Electrical resistivity of Cajon Pass cores at elevated pressures
Authors: Hirsch L. M. , Wang C. ‐Y.
Published: February 2008

The electrical resistivity of rock cores recovered from the Cajon Pass hole ranged from 5 to 46 kΩ‐m, as determined at pressures to 200 MPa and frequencies of 10‐30,000 Hz. The resistivities of cores recovered from depths less than 1.6 km are about one‐order of magnitude greater than the in situ resistivity as measured by the deep Laterolog. However, at greater depths, the laboratory resistivities and those from the deep Laterolog are in fairly good agreement. The results suggest that at these depths the fractures, whether mineralized or fluid‐filled, are no longer well interconnected.
Geochemistry of water at Cajon Pass, California: Preliminary results
Authors: Kharaka Yousif K. , Ambats Gil , Evans William C. , White Art F.
Published: February 2008

Samples of water and associated gases were collected from the Cajon Pass well using downhole samplers, and from the pipe stands at the completion of drill stem tests. The fluids were recovered from fracture systems in granitic rocks from two uncased test intervals located at 1,829 to 1,905 m and 1,829 to 2,115 m. Results of chemical analysis indicate major differences in the composition of water from different fracture systems. Water from one fracture system in the first test interval has a salinity of 2,150 mg/L dissolved solids and is relatively high in Cl, Ca and Fe, but low in HCO3 and SO4; water salinity from a second fracture system is only 950 mg/L and is dominated by Na, HCO3 and SO4. Most of the water from the second interval likely originated from one fracture system; it is alkaline, low in HCO3, has a salinity of 1,150 mg/L, and is a NaSO4 type water characteristic of pore water in the granitic rocks of the area. The differences in water composition indicate different evolutionary paths and isolation of water within relatively proximal fracture systems.
Dissolved gases in the DOSECC Cajon Pass Well: First year results
Authors: Evans William C. , White L. D. , Kharaka Yousif K.
Published: February 2008

Fluid sampled from granitic rock near the 2 km depth in the DOSECC Cajon Pass well contained He, H2, CH4, C2H6, and C2H4 in concentrations much greater than in air‐saturated water. The dissolved helium, which ranged in concentration from 0.6 to 0.8 µmole/kg‐fluid, was almost entirely radiogenic (³He/4He = 0.06 Ra). The δ13C‐CH4 value (−36 per mil) and (C2H6 + C2H4)/CH4 ratios (0.02 ‐ 0.05) indicate that the dissolved methane (50‐55 µmoles/kg‐fluid) was produced by thermogenic breakdown of organic matter. Measured pCO2 values were very low, about 10−5 atm., and the carbon isotopes (δ13C = −18.9 per mil) point to an organic source such as plant root respiration for the dissolved carbonate species. No evidence of mantle volatiles was found despite proximity of the well to the San Andreas fault.
Paleomagnetism of sedimentary rocks from and near the DOSECC Cajon Pass Well, southern California
Authors: Liu Wei , Kirschvink Joseph L. , Weldon Ray J.
Published: February 2008

As part of a larger study of the geologic and tectonic history of the Cajon Pass area, we conducted paleomagnetic studies on sedimentary rocks recovered from the Cajon Pass DOSECC well, and adjacent surface exposures from unit 5 of the late Early to Middle Miocene Cajon Fm. A comparison of the magnetic polarity stratigraphy of the surface and the core sections suggests that they do not match well, which may imply that the rocks at depth have been deformed so that simple extrapolation from the surficial geology to depth is not possible. Although tectonic rotation cannot be inferred from the samples from the core, a clockwise rotation of 30 ± 8.9° was found in unit 5 of the Cajon Fm near the well site at the surface, which is consistent with the results from the same unit 2 km to the west. In contrast, the early Late to late Early Miocene Crowder Fm across the Squaw Peak fault and the youngest unit, unit 6, of the Cajon Fm at the northwestern end of the formation have not been rotated. The rotation of unit 5 near the Squaw Peak fault is thus probably local, caused by drag associated with the fault.
Vertebrate paleontologic investigation, DOSECC “Deep Hole” Project Cajon Pass, San Bernardino County, California
Authors: Reynolds Robert E. , Weldon Ray J.
Published: February 2008

The DOSECC well in Cajon Pass encounters two sedimentary units: the uppermost is Unit 5 of the Cajon (Punchbowl) Formation; the lower has not been identified. To help identify the lower unit, 325 fragments of fossil tooth and bone were separated from 600 kg of cuttings recovered from 430‐435 m in the well by washing, sizing, heavy liquid separation and hand sorting. The most diagnostic fossil is a rodent upper incisor with distinctive pinnate ridges. Such ridges are characteristic of those on upper incisors of Hemingfordian land mammal age squirrels of the tribe Sciurini. This date is consistent with local structural interpretations.
Ion equation of state in quasi‐parallel shocks: A simulation result
Authors: Mandt M. E. , Kan J. R.
Published: February 2008

Ion equation of state in the quasi‐parallel collisionless shock is deduced from simulation results. The simulations were performed for θbn = 10° β = 0.5 and MA in the range from 1.2 to 8, where MA is the Alfven Mach number, β is the upstream ratio of plasma pressure to magnetic pressure and θbn is the angle between the shock normal and the upstream magnetic field. The equation of state can be approximated by a power law with different exponents in the upstream and downstream sides of the shock transition region. The exponent in the upstream side of the transition region is much greater than the adiabatic value of 5/3 and increases with MA. The exponent in the downstream side of the transition region is slightly less than 5/3. The results show that ion heating in the quasi‐parallel shock is highly nonadiabatic with a large increase in entropy and in temperature ratio in the upstream side of the transition region, while the heating is highly isentropic with a large increase in temperature difference across the principal density jump in the downstream side of the transition region.
The effects of recording medium upon reversal records
Authors: Weeks R. J. , Fuller M. , Williams I.
Published: February 2008

The effects of magnetic recording by different rock types upon the appearance of paleomagnetic records of reversals have been simulated using a model of transition fields. Lava records were simulated using a Poisson process. The results are characterized by hangups and impulses which are not present in the reversal model, but resemble observed lava records of reversals. Sedimentary records simulated by smoothing produce predictable attenuation of features of the model, and, if a component of random noise is added, seem to match the appearance of many observed sedimentary records. These numerical experiments suggest that many features that might be interpreted as field behavior may generated by the recording process.
VHF radar measurements of the aspect sensitivity of the summer polar mesopause echoes over Andenes (69°N,16°E), Norway
Authors: Czechowsky Peter , Reid Iain M. , Rüster Rüdiger
Published: February 2008

The mobile SOUSY VHF (53.5 MHz) radar, located near Andenes on the island of Andoya in Northern Norway, has been used to measure the aspect sensitivity of the very strong radar returns obtained from near the summer polar mesopause. This so‐called Polar Mesopause Summer Echo (PMSE) exhibits substantial aspect sensitivity, with angular polar diagrams of the backscatter of 2‐10° half‐width for a two day average. During one three hour period, in which the power received in the antenna vertical beam was particularly intense, the grating lobes of the antenna polar diagram were utilized as additional beams, and the power returned at angles of 35 and 38° off‐zenith was obtained. These measurements provide an estimate of the ratio of the specular to the turbulent contributions to the backscatter.
Concerning the origin of enhanced sodium layers
Authors: Clemesha B. R. , Batista P. P. , Simonich D. M.
Published: February 2008

A mechanism is proposed for the formation of the thin layers of enhanced sodium concentration observed in the atmospheric sodium layer. The proposed mechanism involves the wind‐shear distortion of initially thick sodium clouds of limited horizontal extent, originally produced by the deposition of material of extraterrestrial origin. This mechanism explains almost all the observed characteristics of the enhanced layers, including their height of occurrence, small vertical extent, vertical motion, rapid growth and decay and highly variable duration.
Transmission of solar wind hydromagnetic energy into the terrestrial magnetosphere
Authors: Slawinski R. , Venkatesan D. , Wolfe A. , Lanzerotti L. J. , Maclennan C. G.
Published: February 2008

The relationships of hydromagnetic energy in the band ∼20‐50 mHz, as measured on the ground near a dayside magnetopause field line, to the magnitude of the interplanetary magnetic field (IMF) are examined. While previous investigations of high latitude hydromagnetic waves have focused on a few selected events, this letter reports the results of a statistical study of a large sample of data. Specifically, the present study examines previously reported linear relationships between the physical quantities. When a certain selection criterion is imposed, the distribution of signal frequencies ƒ as a function of IMF magnitude BT has two distinct branches for ƒ∼20‐50 mHz. One branch has ƒ independent of BT while the other has ƒ as a linear function of BT similar to the result of Gul'elmi [1974] from a study based upon lower latitude data and more qualitative, visual criteria. It is suggested that this second branch is probably produced by an upstream wave source, most likely the direct transmission of interplanetary ion cyclotron waves into the terrestrial magnetosphere. The branch independent of BT can have a variety of sources, including surface wave excitation on the magnetopause, waves produced by flux transfer events, and ionospheric processes.
On the possibility of beat excitation of whistler sidebands in the magnetosphere via ponderomotive force
Authors: Tripathi V. K. , Patel V. L.
Published: February 2008

We propose a new mechanism to explain the observed sidebands of whistler waves. The mechanism based on nonlinear interaction has potential application to active experiments in the magnetosphere. The process requires two whistler waves with nearly equal frequency ω1‐ω2 and forward and backward traveling components. They exert a parallel ponderomotive force on the electrons at the difference frequency (ω1‐ω2). The modulation of the plasma density by the nonlinear mixing of these two waves, in conjunction with the oscillatory electron velocity at ω1 and ω2 generates a nonlinear current. This nonlinear current drives the first‐order sidebands. In the presence of low frequency density modulation, the oscillatory velocities at the first‐order sidebands generate second‐order sidebands. The process continues to generate higher order sidebands. The sidebands up to seventh order have been observed in VLF experiment at Siple station. The mechanism is effective for the large amplitude waves.
A coupled thermosphere/ionosphere general circulation model
Authors: Roble R. G. , Ridley E. C. , Richmond A. D. , Dickinson R. E.
Published: February 2008

The NCAR thermospheric general circulation model (TGCM) is extended to include a self‐consistent aeronomic scheme of the thermosphere and ionosphere. The model now calculates total temperature, instead of perturbation temperature about some specified global mean, global distributions of N(²D), N(4S) and NO, and a global ionosphere with distributions of O+,NO+, O2+, N2+, N+, electron density, and ion temperature as well as the usual fields of winds, temperature and major composition. Mutual couplings between the thermospheric neutral gas and ionospheric plasma occur at each model time step and at each point of the geographic grid. Steady state results for this first Eulerian model of the ionosphere, are presented for solar minimum equinox conditions. The calculated thermosphere and ionosphere global structure agrees reasonably well with the structure of these regions obtained from empirical models. This suggests that the major physical and chemical processes that describe the large‐scale structure of the thermosphere and ionosphere have been identified and a self‐consistent aeronomic scheme, based on first principles, can be used to calculate thermospheric and ionospheric structure considering only external sources.
Ground‐based measurements of exospheric hydrogen density
Authors: Kerr R. B. , Tepley C. A.
Published: February 2008

A new observation technique, suggested by recent advance in exospheric theory, appears useful for timely measurement of exospheric atomic hydrogen density, [H]. Fabry‐Perot interferometer measurements of the geocoronal 6563 Å (Hα) emission in the plane of the solar azimuth are used to approximately isolate the singly scattered resonant fluorescent intensity of Hα (ISS) thereby simplifying the derivation of [H]. This initial use of the technique produces profiles of [H] from 400 to 10,000 km. The theoretical bulge of [H] in the early morning hours, previously escaping detection based on simple comparison of relative intensities, is now revealed with a magnitude exceeding the theoretical value. The measured ratio of [H] at 0430 local time to [H] at 2030 local time is 3.0−0.36+0.71 at 700 km, compared with a theoretical value of 1.72. At 2000 km we find no local time variation, in agreement with theory. Unlike nearly all previous studies, we find no arbitrary increase in the solar Lyman beta (Ly‐β) flux is necessary to reconcile derived ISS with current models of exospheric [H]. Deriving absolute [H] remains subject to large systematic uncertainties (on the order of 50%), but the new method substantially improves upon linear extrapolation of relative density variations from Hα intensity changes.
A thermal instability for the spread‐F echoes from HF‐heated ionosphere
Authors: Kuo S. P. , Djuth F. T.
Published: February 2008

A thermal instability is studied for the generation of large‐scale field‐aligned irregularities in the F‐region of the ionosphere. These irregularities are then explained to be the cause of the spread‐F traces in the ionograms recorded in the recent Arecibo heating experiments. The background plasma is assumed to have an elevated electron temperature and a localized heat source located near the HF reflection height. The elevated electron temperature is maintained by the heat source which is supplied by the HF heater. The dispersion relation of the instability is derived and analyzed for the threshold condition and the growth rate. The calculated growth time of the large‐scale irregularities is consistent with the Arecibo observations when measured electron‐to‐ion temperature ratios in the range between 2 and 3 are used in the analysis.
Sulfide in surface waters of the western Atlantic Ocean
Authors: Cutter Gregory A. , Krahforst Christian F.
Published: February 2008

Using newly developed techniques, some preliminary data on hydrogen sulfide in surface waters of the western Atlantic have been obtained. Concentrations of total sulfide range from <0.1 to 1.1 nmol/L, and vary on a diel basis. At these concentrations, sulfide may affect the cycling of several trace metals via the formation of stable complexes. Production of sulfide in oxygenated seawater may occur through the hydrolysis of carbonyl sulfide or by sulfate reduction within macroscopic particles in the water column. Removal mechanisms can include oxidation, complexation with particulate trace metals, and metal sulfide precipitation. However, the temporal and spatial distributions suggest a complex set of processes governing the behavior of sulfide in the surface ocean.
A finite element computation of seismic diffraction about the rise axis magma chamber
Authors: Burnett Mark S. , Orcutt John A. , Olson Allen H.
Published: February 2008

In a previous study, models of the crust and magma chamber at 12°50′N on the East Pacific Rise were derived with a two‐dimensional ray‐tracing analysis of rise‐normal refraction lines. The best model featured a 4 km wide axial magma chamber, but the data contained diffraction effects that were not modeled by geometric ray theory. This raised questions as to whether this model would reproduce the waveform data and whether diffraction might be obscuring a much larger magma chamber. We have tested the model with a finite element calculation of synthetic seismograms. This method incorporates full wave effects, including diffraction. The synthetics accurately reproduce the data and exhibit diffraction phenomena similar to those in the data. The previous travel time analysis was largely successful and was only slightly compromised by diffraction. Diffraction in rise‐normal refraction experiments is, therefore, not obscuring a large, low velocity magma chamber.
Dayside auroral activity and magnetic flux transfer from the solar wind
Authors: Lockwood M. , Sandholt P. E. , Cowley S. W. H.
Published: February 2008

Combined observations by meridian‐scanning photometers and the EISCAT radar show that the "midday‐auroral breakup" phenomenon is associated with major increases in ionospheric flow. A sequence of nine events is observed in the early afternoon MLT sector during a period when the IMF is strongly southward with a large positive By component. Each auroral structure is seen at both 630 and 557.7nm and initially moves westward, accompanied by an increase in potential of 30‐60kV across the north‐south dimension of the EISCAT field‐of‐view. After a few minutes the arc (or arc fragment) moves into the polar cap and fades, and the velocities observed by the radar swing from westward toward northward. We conclude that dayside auroral breakup is closely associated with momentum transfer across the magnetopause which occurs in a series of events 5‐15 minutes apart. The largest of the observed events has dimensions of about 300km (in the direction of westward motion) by 700km, is bounded on its poleward edge by a 5kR arc and is associated with a potential of at least 80kV.
Phase transformations in diopside CaMgSi2O6 at pressures Up to 25 GPa
Authors: Irifune Tetsuo , Susaki Jun‐ichi , Yagi Takehiko , Sawamoto Hiroshi
Published: February 2008

Phase transformations in diopside have been studied at pressures up to 25 GPa and at temperatures of 1100 and 1500 °C by a multiple anvil apparatus. The following phase assemblages are found to be stable at given pressures; diopside (15 and 18 GPa), Mg2SiO4 spinel + stishovite + CaSiO3 perovskite (19 and 20 GPa), MgSiO3 ilmenite + CaSiO3 perovskite (22 GPa), and MgSiO3 perovskite + CaSiO3 perovskite (24.5 GPa). Electron microprobe analysis reveals that the solubility of the MgSiO3 molecule in CaSiO3 cubic perovskite is limited to between 2–5%. The solubility of the CaSiO3 molecule in MgSiO3 orthorhombic perovskite is more restricted, being of the order of 2% or less. These results are contradictory to earlier work in which diopside is reported to transform into a cubic perovskite structure of the same composition above 22–23 GPa.
Can random reconnection on the magnetopause produce the low latitude boundary layer?
Authors: Nishida Atsuhiro
Published: February 2008

We consider consequences of the reconnection that occurs randomly on the dayside magnetopause. Open field lines produced by such reconnection events often intersect with each other, and they do not necessarily show some of the features that would be expected from the reconnection if this mutual interaction were absent. Some of the randomly produced open field lines would re‐reconnect and result in closed field lines. The solar wind plasma streams into the magnetosphere along these field lines as long as they are open, however, and stays there after the field lines become closed again. We propose that this is the mechanism of the plasma supply into the low‐latitude boundary layer. We will show that many of the observed signatures of the LLBL are consistent with this model.
Upper stratosphere polar jet instability in the Southern Hemisphere
Authors: Miles T. , Grose W. L.
Published: February 2008

Synoptic‐scale zonal eddies (longitudinal disturbances) confined to polar latitudes in the southern hemisphere (SH) upper stratosphere have been observed in Fourier analyses of temperature measurements from the Limb Infrared Monitor of the Stratosphere (LIMS) experiment during April‐May 1979. Eddy activity at 60°S, 1 mb is characterized by a Fourier zonal wavenumber 5 (wavelength ∼ 4,000 km) disturbance of amplitude 2‐3 K which exhibits intermittent eastward propagation, substantial meridional phase tilt, and little vertical phase tilt. These wave properties, along with evidence of pronounced latitudinal variations in the upper stratosphere zonal wind distribution, suggest that the synoptic‐scale modes may arise from a latitudinal wind shear (barotropic) instability of the SH polar jet stream. This analysis apparently represents the first identification of polar upper stratosphere synoptic‐scale disturbances from satellite‐based information, heretofore only seen in rocketsonde measurements in northern hemisphere (NH) polar regions and also predicted by linear model studies. The ability to discern these disturbances in satellite temperature data sets offers an opportunity for future studies of the interhemispheric and interannual variability of synoptic‐scale eddy activity in the stratosphere. However, an unambiguous determination of dominant wavelength and phase speed in such studies will be precluded by the fact that satellite data always will suffer from a certain degree of aliasing if disturbances exist with scales unresolved by the asynoptic satellite sampling.
Simulation of the 14‐month chandler wobble in a global climate model
Authors: Hameed Sultan , Currie Robert G.
Published: February 2008

The agent that generates and maintains the 14‐month Chandler wobble of the solid earth about its rotation axis has remained unresolved for a century with first the atmosphere, later earthquakes, and more recently the earth's fluid core proposed as candidates. Here we report that surface air pressure calculated in a coupled ocean‐atmosphere general circulation model (GCM) displays a 14.7 month signal, whose amplitude is similar to that found by Maksimov (1960) in station data; we identify it as the atmospheric Chandler wobble. This result indicates that changes in atmospheric mass distribution excite and maintain the wobble of the solid earth, and that neither earthquakes nor the fluid core are significant contributors. Another result is that in the GCM the amplitude of the wobble at high latitudes is a substantial fraction of the annual cycle, and thus is an important factor in climate formation as Maksimov (1960) suggested.
Measuring complex spectra of long‐period surface waves for earthquake source analysis
Authors: Zhang Jiajun , Lay Thorne
Published: February 2008

Long‐period surface waves from large earthquakes can provide reliable estimates of the source depth, rupture duration, seismic moment, and fault orientation. This requires accurate surface wave phase and amplitude spectra and precise propagation corrections. Standard procedures for estimating spectra of traveling waves in source analyses are inaccurate for periods exceeding 300 s, so the longer periods are usually analyzed by free oscillation analysis if at all. We apply a multiple filter analysis to extract complex spectra for periods up to 500 s suitable for traveling wave spectral inversions. This will allow improved constraints on the rupture process of large earthquakes to be obtained by inversion methods using a single formalism.
Acetonitrile in the air over Europe
Authors: Hamm S. , Helas G. , Warneck P.
Published: February 2008

A gas chromatographic technique was developed to measure acetonitrile mixing ratios in air samples collected during three aircraft flights over Europe. Uniform mixing ratios were observed in the troposphere independent of altitude, with an average of 144±26 pptv for the first two flights, and 194±7 pptv for the third.
The effect of lateral viscosity variations on surface observables
Authors: Koch Dorothy M. , Ribe Neil M.
Published: February 2008

We investigate the effect of lateral viscosity variations on surface observables by considering an idealized model problem: the motion of a deformable fluid sphere of radius a, density ρs and viscosity ηs at a depth d beneath the surface of a fluid half‐space with density ρf and viscosity ηf. We derive a semi‐analytical solution for the flow in bipolar spherical coordinates, from which we calculate the surface velocity divergence, the surface topography, and the geoid anomaly above the sphere. Lateral viscosity variations have a large (≥ 50%) effect on these surface observables when the load is relatively “hard” (γ = ηs/ηf > 1) and shallow (λ = d/a < 1.5), but a small (< 15%) effect when the load is “soft” (γ ≪ 1) or deep (λ≥ 2.5). The geoid anomaly produced by a soft upwelling plume differs only slightly (∼ 13%) from that produced by an isoviscous (γ = 1) plume. The viscosity contrasts (γ ≫ 1) associated with subducted slabs have a larger effect on the geoid. Geoid models which include such viscosity contrasts may therefore require a greater viscosity increase with depth than existing models which assume isoviscous slabs.
Stratospheric ozone measurements with a tunable diode laser heterodyne spectrometer
Authors: Okano S. , Taguchi M. , Fukunishi H.
Published: February 2008

The vertical mixing ratio profiles of stratospheric ozone have been obtained through an inversion of the ozone absorption spectra in the 9µm band measured by a tunable diode laser heterodyne spectrometer with a spectral resolution of 80 MHz (0.0027 cm−1). The observations were made on June 22, 1988, and on August 22, 1988, at Sendai (38°15′N, 140°50′E), Japan. The values of the signal‐to‐noise ratio of the observed spectra are 190 for the data of June 22, 1988, and 300 for the data of August 22, 1988. The accuracy of the mixing ratio and the vertical resolution is examined. The results are compared with data obtained by Dobson spectrophotometers and an ozonesonde.
The universal time variation of geomagnetic activity
Authors: Russell C. T.
Published: February 2008

Geomagnetic activity exhibits both annual and daily variations. We examine these variations in the Am index which was designed to provide an accurate measure of the Universal Time variation of geomagnetic activity. The dayside reconnection process can quantitatively account for the observed variation in both indices. Control of these variations by the angle of the flow relative to the dipole axis is weaker than control by reconnection.
EISCAT observations of strong ion outflows from the F‐region ionosphere during auroral activity: Preliminary results
Authors: Wahlund J‐E. , Opgenoorth H. J.
Published: February 2008

Observations of large outward field‐aligned flows of the bulk ion population in the F region during auroral activity are presented. These ion outflows are most commonly observed within auroral arcs, and are not well correlated with diffuse aurora. The ions (mainly O+) may reach field‐aligned outward velocities of more than 500 m/s and the calculated ion fluxes usually reach 1013 m−2 s−1. Strong electron temperature enhancements in the F region are observed in connection with almost all ion outflow events. However, high electron temperatures are not always an indicator for these strong ion outflow events. Our measurements have been carried out at the EISCAT incoherent scatter facility near Tromsø, Norway. The exact mechanism causing the ion outflow is not yet understood, but several possible mechanisms are briefly discussed.
Formation of polar cap arcs
Authors: Chiu Y. T.
Published: February 2008

It is shown that polar cap arcs of typical electron energy ≤ 1 keV can be produced by the downward acceleration of polar rain electrons by parallel potential drops on open field lines. The formation of these arcs is the result of current response to meso‐scale velocity shear structures in the ionospheric convection that is not matched at the magnetosphere. The theory predicts the formation of a pair of meso‐scale field‐aligned currents (one upward and one downward) for each ionospheric shear structure. The theory does not require a bifurcated magnetic configuration for each polar cap arc; hence, it can account for the frequently encountered multiple polar cap arcs without cutting up the magnetosphere into a large number of open and closed magnetic field regions.
Identification of relict phases in a once‐molten Allende Inclusion
Authors: Kuehner Scott M. , Davis Andrew M. , Grossman Lawrence
Published: February 2008

Fassaite rims around spinel grains that are enclosed entirely by normally zoned cores of melilite crystals are interpreted as relict grains which predate the melting of Allende Type B1 refractory inclusions. Nonrelict, subliquidus fassaite did not begin crystallizing from melts of these compositions until the onset of precipitation of the reversely zoned melilite mantles around the same melilite crystal cores. Relict fassaite is fractionated and highly enriched in REE and other refractory lithophiles compared to subliquidus fassaite in the same inclusion. Mass balance suggests that the relict fassaite represents only 3% of the original premelt amount of fassaite, and that melilite and at least one other phase were additional condensate precursors of these inclusions.
A basic limitation of the split window method for SST retrievals when applied to a wide range of water vapor conditions
Authors: Hagan Denise E.
Published: February 2008

The split window method for retrieving sea surface temperatures (SST) from satellite‐based observations is evaluated from radiative transfer calculations, and shown to have an inherent limitation that arises from a linear assumption in the correction scheme. This general limitation leads to significant errors (of several degrees in some cases) in the retrieved SST; the theoretical basis for the error is examined.
Comparison of near‐coincident crustal refraction and extended vibroseis reflection data: Peace River Region, Canada
Authors: Zelt C. A. , Ellis R. M.
Published: February 2008

A 10‐km‐long uncorrelated Vibroseis data set was processed to test the feasibility of using industry reflection data for deep crustal imaging in the Peace River region and elsewhere in the Western Canada Sedimentary Basin. These results were compared with a crustal refraction interpretation of a line ∼10 km to the north. The Vibroseis data were extended from a conventional 3 s to 14 s two‐way travel time using the self‐truncating‐sweep method. The reflection section contains a prominent eastward‐dipping event at ∼9.4 s (29 km depth) which corresponds to the zero‐offset two‐way travel time of an intracrustal boundary in the refraction model. This may represent the Riel discontinuity imaged at similar depths in southern Alberta. A series of near‐vertical incidence reflections over 1–1.5 s terminating at 13 s corresponds well with the refraction Moho at 12.8 s (41 km depth). This suggests that locally, the crust‐mantle boundary is a complex, possibly layered transition zone of 3–5 km thickness.
Grain‐size dependence of the magnetic behavior of pyrrhotite during its low‐temperature transition at 34 K
Authors: Dekkers M. J. , Mattéi J.‐L. , Fillion G. , Rochette P.
Published: February 2008

The grain‐size dependent behavior of pyrrhotite during a magnetic LT‐transition at 34 K is suitable for granulometric purposes. Cycling down to liquid Helium temperature suppresses soft MD Jrs more than hard SD Jrs, so that it may be effective in removing soft secondary NRM components. The domain structure of large pyrrhotite grains changes from MD at room temperature to SD or PSD below the LT‐transition.