bluuebunny/crossref_metadata_2025 huggingface dataset:
The scientific objectives of the ATLAS‐1 shuttle mission
Authors: Torr Marsha R.
Published: February 2008

During the 9‐day ATLAS‐1 mission (March 24 – April 2, 1992), a significant database was acquired on the temperature, pressure, and composition of the atmospheric regions between approximately 15 km and 300 km, together with measurements of the total solar irradiance and the solar spectral irradiance between 1200 Å and 3.2 μm. Six remote sensing atmospheric instruments covered a scope in altitude and species that has not been addressed before from a single mission. The atmospheric composition dataset should serve as an important reference for the determination of future global change in these regions. Both the solar and atmospheric instruments made observations that were coordinated with those made from other spacecraft, such as the UARS, the NOAA, and the ERB satellites. The objective of these correlative measurements was both to complement the measurements made by the other payloads and also to update the calibration of the instruments on the long‐duration orbiting vehicles with recent, highly accurate calibrations. Experiments were conducted in space plasma physics. Most important of these was the generation of artificial auroras by firing a beam of energetic electrons into the atmosphere. The induced auroras were observed with a photometric imaging camera. In addition, measurements were made of the precipitation of energetic neutrals from the ring current. ATLAS‐1 also carried an UV instrument to gather wide field observations of astronomical sources. A subset of these instruments is planned to fly once a year for the duration of a solar cycle. Both the ATLAS‐1 mission and the ongoing series represent an important element of the Mission to Planet Earth and the Global Change Program. The papers in this special issue give a summary of the results obtained in the first 4 months following the mission.
Evolution of seafloor spreading rate based on 40Ar degassing history
Authors: Tajika Eiichi , Matsui Takafumi
Published: February 2008

A new degassing model of 40Ar coupled with thermal evolution of the mantle is constructed to constrain the temporal variation of seafloor spreading rate. In this model, we take into account the effects of elemental partition and solubility during melt generation and bubble formation, and changes in both seafloor spreading rate and melt generation depth in the mantle. It is suggested that the seafloor spreading rate would have been almost the same as that of today over the history of the Earth in order to explain the present amount of 40Ar in the atmosphere. This result may also imply the mild degassing history of volatiles from the mantle.
Seismic transmission survey: Application to real data from microearthquakes
Authors: Katsumata Kei
Published: February 2008

Two discontinuities have been discovered which are closely related to the Philippine Sea (PHS) plate that subducts beneath the Kanto district in Central Honshu, Japan. A seismic transmission survey method is used to image discontinuities in the Earth from mode converted transmission (MCT) waves, and this method is applied to aftershocks of an event which occurred beneath the southern Tokyo Bay at a depth of 100 km. As a result, two predominant interfaces at depths of 24 km and 35 km appear in the section of P→SV MCT waves. This example demonstrates that the seismic transmission survey method proposed by Katsumata (1992) should be very useful in studying fine structure in the Earth. Moreover, it indicates that even microearthquakes can be used as sources for seismic surveys.
Intercomparison of total ozone data from Nimbus 7 TOMS, the Brewer UV Spectrophotometer and SAOZ UV‐Visible Spectrophotometer at High Latitudes Observatory, Sodankylä
Authors: Kyrö Esko
Published: February 2008

The use of visible spectroscopy makes it possible to measure stratospheric constituents when Solar Zenith Angle (SZA) is as large as 93°. This fact allows the daily measurements of ozone and other species throughout the year at and beyond the latitudes of the polar circle. Because the visible spectroscopy is a new technique in ozone monitoring, it is useful to compare it with the classical uv spectroscopy. At Sodankylä the widely‐used SAOZ uv/visible spectrophotometer (Système d'Analyse et d'Observations Zénithales) and the modem uv spectrophotometer Brewer have been measuring side by side since early 1990. This paper reports the first long‐term intercomparison between the daily total ozone values measured by the SAOZ and the Brewer covering the period from February 1990 to June 1991. As a reference the intercomparison between the Brewer and TOMS (Total Ozone Mapping Spectrometer) instruments from May 1988 to December 1991 is also reported.
Local time occurrence frequency of energetic ions in the Earth's magnetosheath
Authors: Fuselier S. A. , Hill P. , Baumjohann W. , Gosling J. T.
Published: February 2008

The occurrence frequency of energetic ions in the energy range from 8 to 40 keV/e as a function of local time in the magnetosheath is presented. Energetic ions are observed in the magnetosheath with a minimum probability of 25% for all local times. The occurrence frequency for the energetic ions is higher on the dawnside than on the duskside but shows a relative maximum post‐noon in the local time range from 12 to 15 hours. The post‐noon relative maximum is attributed to a magnetospheric source for the energetic ions while the dawn‐dusk asymmetry is attributed to a quasi‐parallel bow shock source.
Measurements of the evolution of the Mt. Pinatubo aerosol cloud by ISAMS
Authors: Lambert A. , Grainger R. G. , Remedios J. J. , Rodgers C. D. , Corney M. , Taylor F. W.
Published: February 2008

Measurements by the Improved Stratospheric and Mesospheric Sounder (ISAMS) on the Upper Atmosphere Research Satellite (UARS) are being used to study the spatial and temporal evolution of the volcanic stratospheric aerosol from Mt. Pinatubo. The maximum opacity of the aerosol cloud moved from a position south of the Equator at an altitude of about 26 km in early October 1991, became located over the Equator by mid‐January 1992, and descended in altitude to about 21 km by July 1992. Dispersal of the cloud was more rapid in the Southern Hemisphere and penetration to the southern polar region occurred earlier than transport to the corresponding northern polar area. The area weighted global mean stratospheric optical thickness between 15 km and 35 km at 12.1 μm remained at about 5.5×10−3 from November 1991 through to April 1992. The estimated aerosol mass loading is 19–26 megatonnes for this period and by the end of July 1992 it had declined to 15–21 megatonnes.
Turbulent flow microstructures observed by sonar
Authors: Lhermitte R. , Lemmin U.
Published: February 2008

This note presents observations of sound wave backscattering in a turbulent water flow, conducted with a frequency scanning Doppler sonar working in a 0.5 to 5 MHz frequency band. The observed sound wave backscattering is attributed to temperature microstructures created by water turbulence. The backscattering intensity decreases systematically as a function of sonar frequency above 1 MHz and falls below detectability for sonar frequencies higher than a given value function of water turbulence intensity. This backscattering cutoff relates to the high wavenumber end, kB, of the turbulent temperature spectrum. This kB estimate is found in excellent agreement with its theoretical calculation based on independent measurement of turbulence dissipation rate made using the Doppler observed velocity variance.
A new type of ion injection event observed by Viking
Authors: Yamauchi M. , Woch J. , Lundin R. , Shapshak M. , Elphinstone R.
Published: February 2008

A new type of low energy (< 200 eV) plasma injection event is found near local noon several degrees equatorward of the cusp. Its V‐shaped energy‐pitch angle pattern is very similar to that of impulsive or transient magnetosheath plasma injection events reported in the past. Thus, the source region of these injected particles is not a persistent one and that it is likely of magnetosheath origin. However, there are three facts which distinguish this newly found phenomenon from the other impulsive or transient magnetosheath plasma injection events associated with solar wind pressure pulse or southward/fluctuating interplanetary magnetic field conditions. First, the magnetic field and the electric field observations do not show such a strong electromagnetic coupling between the ionosphere and the source region. Second, a high energy (> 300 eV) population is absent, making the ion energy‐time dispersion very weak. Third, this event does not seem to be related to either any solar wind density increase or southward/disturbed interplanetary magnetic field conditions. These observations suggest that this is a more stagnant phenomenon, and we propose to call this a “Stagnant Plasma Injection” event.
Porosity and consolidation limits of sediments and Gassmann's Elastic‐Wave Equation
Authors: Nolen‐Hoeksema Richard C.
Published: February 2008

The elastic framework properties of sediments relate to porosity. Porosity relates to the state of consolidation of sediments. The full range of quasi‐static, elastic moduli vs porosity behavior can be incorporated into Gassmann's [1951] equations. I review the Atterberg [1911] limits to establish a basis for discussing the precompaction porosity, ф0, which corresponds approximately to the Atterberg plastic limit. This porosity is about 0.36–0.40 for sands and sandstones. The ratio of the dry‐frame moduli to the effective mineral moduli is (1−ф/ф0). I incorporate this ratio into Gassmann's equations, which operate from 0 ≤ ф ≤ ф0, when sediments have a solid elastic frame. For ф s> ф0, when sediments no longer have a solid elastic frame, Gassmann's equations reduce to Reuss' [1929] isostress average for the solid‐fluid mixture.
Airborne measurement of absolute sea‐surface heights
Authors: Brozena John M. , Peters Mary F. , Forsberg Rene
Published: February 2008

Topographic profiles may be measured from an aircraft by differencing precise radar or laser altitudes with ellipsoidal heights obtained by means of kinematic interferometric‐mode GPS. Over the ocean, the difference between the two altitudes is the geoid height plus dynamic oceanographic effects such as tides, currents, eddies, etc. Aircraft might provide, on a local scale, altimetry measurements similar to those from GEOSAT and ERS‐1. Such airborne measurements could be applied to the determination of a local high‐resolution geoid or for oceanographic studies.

Several long over‐water altimetry profiles were obtained during the 1991 field campaign of the Greenland Aerogeophysics Project (GAP91). Kinematic interferometric GPS between multiple short or zero‐baseline airborne receivers and several sets of stationary GPS receivers on the ground provided precise three‐dimensional positioning for airborne gravity, magnetic and topographic profiling sensor systems mounted aboard a P‐3 Orion aircraft. The logistics of surveying a large region (long GPS baselines and poor satellite coverage) limit the accuracy of the GPS positioning, but the geoid signal is clearly visible in the over‐water profiles. In spite of GPS baseline lengths of up to 1000 km, differences between modeled geoid heights and measured sea‐surface heights ranged from about 1–2 meters r.m.s. Although the differences are primarily due to errors in the GPS positions, some portion is due to errors in the model geoid, uncompensated tides, sea‐ice contamination of the radar data and other errors in the radar. We believe that this represents the first airborne measurement of absolute sea‐surface heights.
Volcanic aerosol layers observed by lidar at South Pole, September 1991–June 1992
Authors: Cacciani Marco , Di Girolamo Paolo , di Sarra Alcide , Fiocco Giorgio , Fuà Daniele
Published: February 2008

During 1991 the terrestrial stratosphere went through a substantially increased aerosol load, due mainly to the eruptions of Mt. Pinatubo in the Philippines, and, to a lesser extent, to those of Mt. Hudson in Chile. This paper reports lidar observations of the stratospheric aerosols at South Pole. Two layers were present at different altitudes during the austral summer, but only the higher one persisted in the stratosphere until the onset of the polar stratospheric cloud (PSC) phenomenon. Data have been analyzed in terms of the integrated backscattering coefficient and the aerosol mass content has been estimated.
Growth of aerosols in Titan's atmosphere and related time scales: A stochastic approach
Authors: Rannou P. , Cabane M. , Chassefière E.
Published: February 2008

The evolution of Titan's aerosols is studied from their production altitude down to the ground using a stochastic approach. A background aerosol distribution is assumed, obtained from previous Eulerian modelling, and the evolution of a “tagged” particle, released near the formation altitude, is followed by simulating in a random way its growth through coagulation with particles of the background distribution. The two distinct growth stages, proposed by Cabane et al. (1992) to explain the formation of monomers and subsequent aggregates, are confirmed. The first stage may be divided into two parts. Firstly, within ≈1 terrestrial day, particles grow mainly through collisions with larger particles. They reach their size of monomer (rm ≈0.09 µm) through typically one to five such collisions. Secondly, within a few terrestrial days to ≈1 terrestrial month, particles evolve mainly by collisions with continuously created small particles and acquire their compact spherical structure. In the second stage, whose duration is ≈30 terrestrial years, or one Titan's seasonal cycle, particles grow by cluster‐cluster aggregation during their fall through the atmosphere and reach, at low stratospheric levels, a typical radius of 0.4–0.5 µm.
Ammonium to sulphate ratio in aerosol and snow of Greenland and Antarctic regions
Authors: Silvente Eric , Legrand Michel
Published: February 2008

NH4+ to SO4−− ratio of aerosols and snows are investigated in Greenland. Data suggest that the atmospheric NH4+ and SO4−− signals are well preserved in snow and that previous discrepancies sometimes observed between the composition of the air and that of the snow were probably due to NH4+ artifacts. This study leads to the conclusion that NH3 is not able to neutralize the acidity of the high latitude atmosphere in particular in the Southern Hemisphere.
Constraints on lithospheric thermal structure for the Indian Ocean from depth and heat flow data
Authors: Shoberg Tom , Stein Carol A. , Stein Seth
Published: February 2008

Models for the thermal evolution of oceanic lithosphere are primarily constrained by variations in seafloor depth and heat flow with age. These models have been largely based on data from the Pacific and Atlantic Ocean basins. We construct seafloor age relations for the Indian Ocean which we combine with bathymetric, sediment isopach and heat flow data to derive curves for depth and heat flow versus age. Comparison of these curves with predictions from three thermal models shows that they are better fit by the shallower depths and higher heat flow for the GDH1 model, which is characterized by a thinner and hotter lithosphere than previous models.
Possible effects of anthropogenically‐increased CO2 on the dynamics of climate: Implications for ice age cycles
Authors: Saltzman Barry , Maasch Kirk A. , Verbitsky Mikhail Ya.
Published: February 2008

A dynamical model, developed to account for the observed major variations of global ice mass and atmospheric CO2 during the late Cenozoic, is used to provide a quantitative demonstration of the possibility that the anthropogenically‐forced increase of atmospheric CO2, if maintained over a long period of time (perhaps by tectonic forcing), could displace the climatic system from an unstable regime of oscillating ice ages into a more stable regime representative of the pre‐Pleistocene. This stable regime is characterized by orbitally‐forced oscillations that are of much weaker amplitude than prevailed during the Pleistocene.
Nucleophilic substitution rates and solubilities for methyl halides in seawater
Authors: Elliott Scott , Rowland F. Sherwood
Published: February 2008

Ozone depletion potentials indicate that methyl bromide is among halogen containing gases which may be scheduled for international level regulation. The oceanic component of its global budget is currently unquantifiable because of a lack of surface seawater measurements. Given values for internal removal and for solubility, marine mixed layer modelling can set bounds for air‐sea transfer. Rate constants have been measured in seawater, 0.5m NaCl and distilled water for attack on methyl bromide by the chief oceanic nucleophiles chloride ion and H2O, over much of the oceanographic temperature range (0°C to 22°C). Henry's Law constants have been determined for the same conditions. All results are consistent with classical aqueous phase research adjusted for ionic strength effects. The lifetime of methyl bromide with respect to chemical decay in seawater is three weeks at average surface temperatures, and a factor of ten larger and smaller at the extremes. Its dimensionless solubility ranges from 0.1 to 0.3. Analogous experiments are reported for the other natural methyl halides, CH3Cl and CH3I.
MLS observations of stratospheric waves in temperature and O3 during the 1992 southern winter
Authors: Fishbein E. F. , Elson L. S. , Froidevaux L. , Manney G. L. , Read W. G. , Waters J. W. , Zurek R. W.
Published: February 2008

The Microwave Limb Sounder observed waves in stratospheric temperature and O3 during the 1992 southern winter. Wave 1 intensifies three times from mid August through mid September, when a 9 day eastward traveling wave becomes in phase with the stationary wave 1. During the periods of wave intensification, minor sudden warmings and increased zonal mean O3 are observed. The waves have a westward phase tilt which results in an intensified baroclinic zone when the waves are in phase. Waves in T and O3 are positively correlated near 5–10 hPa, implying transport by planetary waves; this is supported by larger O3 wave amplitudes than expected from photochemistry alone.
By fluctuations in the magnetosheath and azimuthal flow velocity transients in the dayside ionosphere
Authors: Newell Patrick T. , Sibeck David G.
Published: February 2008

Most researchers agree that ionospheric convection is controlled by the magnetosheath By and Bz components and by sheath flows. However transient changes in ionospheric flows are nonetheless generally attributed to transient changes in the merging rate. In particular, bursts in the azimuthal flow velocity and associated auroral transients are often associated with Flux Transfer Events (FTEs). We propose a simple but apparently overlooked alternative: ionospheric flow transients are directly driven by changes — abrupt but not necessarily transient — in the magnetosheath flows and fields. For example, an increase in the sheath By component drives faster flows eastward or westward; while a decrease in the magnitude of By leads to a transient propagating largely poleward. It would not be surprising if changing magnetosheath conditions led to changes in merging behavior; but we emphasize that azimuthal flow velocity changes in the ionosphere do not intrinsically imply any change in the merging rate. Changing the merging rate simply alters the number of field lines which are executing the same sequence of motions. In our model, auroral transients are caused by the velocity shears associated with changing convection patterns imposed on the ionosphere by an altered set of magnetosheath conditions. We point out also that many observational difficulties are resolved if merging occurs continuously, and sheath transients directly drive ionospheric transients. For example, auroral transients frequently convect through the pre‐existing optical cusp; whereas if there has been no change in the sheath parameters any new merging should not move relative to the equally open cusp field lines. It is because of the variability in the sheath parameters that variability in ionospheric convection is imposed. The sources of such sheath field variability include intrinsic IMF variations; variations created at the bowshock; and compression of the sheath field by a variable plasma pressure.
Observations of the plasma flow in comet P/Swift‐Tuttle
Authors: Brown Michael E. , Johns Christopher M. , Spinrad Hyron
Published: February 2008

We present direct ground based observations of the plasma flow sunward and tailward of the nucleus of comet P/Swift‐Tuttle. The observations are long‐slit high resolution spectra of the H2O+ emission centered at 6199Å with a velocity resolution of about 7 km s−1 (FWHM) and a spatial resolution of about 104 km at the comet. Emission is visible from just inside the predicted position of the cometopause on the sunward side of the nucleus out to 5×105 km on the tailward side. The deceleration of the solar plasma on the sunward side is clearly observed as is the acceleration of cometary ions into the tail. These observations show the effectiveness of ground based methods for the systematic study of cometary plasmas and point to the need for a better theoretical understanding of their acceleration mechanisms.
Source parameters of the 1957 Aleutian Earthquake from tsunami waveforms
Authors: Johnson Jean M. , Satake Kenji
Published: February 2008

We studied the source parameters of the 1957 Aleutian earthquake using tsunami waveform data recorded on tide gauges around the Pacific Ocean. Using a finite‐difference computation, this tsunami can be numerically simulated. The tsunami records were inverted for the slip distribution on the rupture area. Results show that slip was concentrated in the western half of the aftershock zone with a maximum displacement of 7m. The moment computed from the slip distribution is 88×1020 Nm, giving the 1957 earthquake a moment magnitude of Mw=8.6. The waveform inversion confirms that no slip occurred in the Unalaska Island area, making this area a possible seismic gap with a potential to rupture in a great earthquake and generate a Pacific‐wide tsunami.
Paleomagnetic and rock magnetic investigations of the Changxing Permian‐Triassic section, Zhejiang Province, China
Authors: Dobson Jon Paul , Heller Friedrich , Li Zheng‐Xiang , Mauritsch Hermann
Published: February 2008

Paleomagnetic and rock magnetic experiments on the Triassic Yinkeng Formation and the Permian Changxing Formation sampled from the Permian‐Triassic type section, Changxing County, reveal that a high temperature primary direction is isolated in dolomitic samples from the Early Triassic but the Late Permian limestones samples appear to be remagnetized during the Jurassic. A Permian‐Triassic pole previously reported for the Changxing Formation from this section (Lin et al., 1985) is not in agreement with results from this study or other poles for that time interval reported for the Yangtze Block and may be remagnetized.
Sudden impulses at low latitudes: Transient response
Authors: Russell C. T. , Ginskey M.
Published: February 2008

When the magnetosphere is compressed by a sudden change in the solar wind dynamic pressure, the horizontal component of the Earth's magnetic field is increased at low latitudes. Often there is an overshoot associated with this increase in the field, but not always. The overshoot does not appear to be due to induced currents in the interior of the Earth or in the ionosphere. Rather, its magnitude appears to be controlled by both the strength of the ring current, and by local time. We speculate that the overshoot in the horizontal component is due to an overshoot in the compression of the magnetosphere and that when the ring current is strong the compressional wave is damped and the magnetosphere is not set into oscillation by the compressional wave.
Geometry of the Benioff Zone and state of stress in the overriding plate in central Mexico
Authors: Singh Shri Krishna , Pardo Mario
Published: February 2008

Analysis of depths and focal mechanisms of 16 small earthquakes in Central Mexico, along with previous data, shows that (a) the subducted Cocos plate becomes subhorizontal between 110 and 275 km from the trench reaching a depth of about 50 km, and (b) the bottom part of the overriding continental plate is in tensional stress regime. Neotectonic structures in Central Mexico and stress orientations (estimated from borehole elongations, cinder cone alignments, and fault‐slip analysis) in the Trans Mexican Volcanic Belt, which lies in the northeastern portion of the area under study, also indicate the same stress regime. Absolute motion of the North American plate in the region has a component normal to the trench of 20 mm/yr which, if true, would result in compressional stress in the upper plate if the trench position is fixed in an absolute frame of reference. If we allow for seaward retreat of the trench then the tensional stress in the overriding plate and the observed geometry of the Benioff zone can be explained. This, however, implies that seaward retreat of a trench is possible even for a young (∼15 m.y. old) subducting slab. Alternatively, tectonic erosion of the leading edge of the continent, which has been proposed to explain truncated igneous and metamorphic continental terrane, could give rise to the tensional stress but would not explain the geometry of the Benioff zone.
Time variations of solar UV irradiance as measured by the Solstice (UARS) instrument
Authors: London Julius , Rottman Gary J. , Woods Thomas N. , Wu Fei
Published: February 2008

An analysis is presented of solar ultraviolet irradiance measurements made by the SOLSTICE spectrometers on the Upper Atmosphere Research Satellite (UARS). Reported observations cover the wavelength interval 119–420 nm, and the analysis discussed here is for the time period 26 Nov 1991 to 31 Dec 1992, during which time solar activity decreased in intensity. At the time of peak activity, the average 27‐day variation had a relative amplitude of ∼8% at Ly‐α, tailing off to about 0.6% at 260 nm. It is shown that over the spectral interval 119–260 nm, the relative 27‐day harmonic was about a factor of two larger during the strongly disturbed as compared with the moderately disturbed period.
2‐D migration velocity estimation using a genetic algorithm
Authors: Jervis Michael , Stoffa Paul L. , Sen Mrinal K.
Published: February 2008

We address the problem of velocity estimation in heterogeneous media using a combination of nonlinear inversion and migration velocity analysis. In velocity estimation, the travel time information in seismic reflection data are nonlinearly related to the velocity perturbations in the subsurface. By taking a functional of seismic traces, the migrated data themselves, we define a misfit criterion which greatly reduces the oscillatory nature of the objective function. Migration is inherently a smoothing process; it collapses diffractions, focuses reflected energy and suppresses random noise. We use the lateral consistency of reflectors after migration as a measure of model misfit. If we compare one migrated shot record with an adjacent record, the misfit will be only slightly affected by large velocity variations even though reflectors may show large errors in depth positioning. The closer the spacing between shot records the smaller the variations in misfit; hence the smoother the objective function.

We search for global minima of the objective function thus defined, using a genetic algorithm (GA) and a linearized inversion scheme. We illustrate the techniques and results from the algorithms by applying them to a realistic scale synthetic data set. As expected, the success of a linearized scheme depends strongly on the starting model while GA does not depend on the choice of the initial population of models. GA is computationally intensive but our choice of spline parameterization reduces the number of model parameters significantly and makes the algorithm computationally tractable for real earth problems.
The heterogeneous interaction of NO2 with amorphous carbon
Authors: Tabor Kevin , Gutzwiller Lukas , Rossi Michel J.
Published: February 2008

From uptake measurements of NO2 on solid amorphous carbon in the mTorr pressure range and at ambient temperature an accommodation coefficient for NO2 of (4.8±0.6)·10−2 has been measured. These experiments reveal a complex chemical mechanism. The only major product observed is NO whose yield corresponds to about 60% of the NO2 adsorbed on the surface. Thermal desorption of a carbon sample that has been exposed to NO2 yields CO and CO2 along with some NO3 and/or N2O5. H2O does not interact measurably at ambient temperature with the type of carbon used in the present study.
MLS observations of lower stratospheric ClO and O3 in the 1992 southern hemisphere winter
Authors: Waters J. W. , Froidevaux L. , Manney G. L. , Read W. G. , Elson L. S.
Published: February 2008

UARS MLS measurements of ClO in the 1992 southern hemisphere winter are described. Lower stratospheric ClO abundances greater than 1 ppbv were observed in the vortex beginning 1 June. The enhanced ClO reached largest areal extent in mid‐August, then retreated poleward. ClO abundances at 22 hPa decreased in early September while those at 46 hPa remained high. O3 decrease within the vortex was observed by mid‐August, and was coincident with the enhanced ClO.
Correction to “Changes in the Earth's rotation by tectonic movements”
Authors: Vermeersen L. L. A. , Vlaar N. J.
Published: February 2008

Present‐day true polar wander and the secular non‐tidal acceleration of the earth are usually attributed to post‐glacial rebound. In the models which relate this rebound to changes in rotation, the mantle is assumed to relax passively to the melted ice‐loads. The lithosphere is usually modeled as a highly viscous upper layer in these models, having viscosities which exceed mantle viscosities by several orders of magnitude.

We propose that lithospheric processes unrelated to post‐glacial rebound and taking place under non‐isostatic conditions are also able to induce non‐negligible influences on the earth's rotation. Examples of such processes are mountain building and erosion, foundering flexure of oceanic basins and lithospheric snapbacking resulting from detachment of subducting slabs. Lithospheric and crustal rheologies and intraplate‐stresses are the dominant factors in these mechanisms, contrary to the mantle rheologies which are assumed to dominate the process of post‐glacial rebound.
Variations in oceanic crustal structure and implications for the fine‐scale magnetic anomaly signal
Authors: Tivey Maurice A. , Johnson H. Paul
Published: February 2008

Marine magnetic anomalies are traditionally modelled using a constant thickness source layer, usually defined as the extrusive lavas associated with seismic layer 2A. Recent seismic studies reveal that the thickness of layer 2A can vary by more than a factor of two, an observation which has important implications for the magnetic anomaly source layer. We model deep‐tow magnetometer data from the Endeavour Segment of the Northern Juan de Fuca Ridge, in combination with nearby seismic data and find a positive correlation between the thickness of the seismically‐defined layer 2A and the magnetic anomaly source layer. This suggests that short‐wavelength magnetic anomalies observed within individual magnetic polarity units can arise from variations in the thickness of the extrusives, rather than geomagnetic field variations or secondary magnetization.
Ozonesonde measurements at Hilo, Hawaii following the eruption of Pinatubo
Authors: Hofmann D. J. , Oltmans S. J. , Harris J. M. , Komhyr W. D. , Lathrop J. A. , DeFoor T. , Kuniyuki D.
Published: February 2008

Ozonesonde measurements at Hilo, Hawaii (20°N), after the eruption of Pinatubo in June 1991, are compared to measurements made there from 1985 to 1990 in order to investigate possible volcanic effects. The general nature of the ozone anomalies in 1991–92 can be summarized as lower than normal ozone below about 25 km and higher than normal ozone above. The net result was that total ozone was somewhat lower than average and, during late 1992, was as low as recorded in 1982, following the eruption of El Chichón. Elevated temperatures in the region of the volcanic aerosol layer and upward motion of the aerosol layer were observed at Hilo following the eruption. Although the nature of the perturbed ozone profile may be the result of enhanced upward motion associated with volcanic aerosol particle heating, and the coupling of quasi‐biennial oscillation effects, the persistent nature of the perturbation, still present more than a year after the eruption, is not easily explained.
A new magnetic pumping accelerator of charged particles in Jupiter's magnetosphere
Authors: Mu Jian‐lin
Published: February 2008

This paper proposes an acceleration mechanism to explain the observations of energetic particles in the inner magnetosphere of Jupiter. In the inner magnetosphere particles are convected towards and away from the Io plasma torus by the centrifugally driven interchange mode or by the longitudinal asymmetry of the magnetosphere and the Io plasma torus. They experience a varying (space‐dependent in Jupiter's frame of reference) magnetic field and are subject to pitch‐angle scattering by wave‐particle interactions. Thus, an e‐fold magnetic pumping acceleration is expected in the system. The calculations show that the accelerator can generate up to one MeV energy particles in about 10–15 times the characteristic convection time.
Near‐surface deformation in the New Madrid Seismic zone as imaged by high resolution SH‐wave seismic methods
Authors: Woolery Edward W. , Street Ron L. , Wang Zhenming , Harris James B.
Published: February 2008

Over 1.5 kilometers of high‐resolution, SH‐wave refraction and reflection profiles have been performed in the Madrid Bend area of northwestern Tennessee, approximately 8 km north of Tiptonville, Tennessee, to establish the existence of neo‐tectonic, near‐surface deformation. The specific area was chosen because of the access it provided to the Tiptonville dome (a Holocene flexure) and the trend of contemporary seismicity within the New Madrid seismic zone (NMSZ). We believed the highest likelihood of near‐surface deformation to be over these features. Partially reversed refraction/reflection walk‐away tests and common depth point (CDP) seismic profiling, using the non‐traditional SH‐wave method, have traced antiformal flexure and numerous faults into the late Eocene and Holocene sediments of the Tiptonville dome province of the Lake County uplift (LCU). Vertical displacements exhibited across the faults range from approximately 3 to 30 m. These structures have been interpreted to be neo‐tectonic features associated with tensional stresses across the Tiptonville dome.
Interpretation of NOx/NOy observations from AASE‐II using a model of chemistry along trajectories
Authors: Kawa S. R. , Fahey D. W. , Wilson J. C. , Schoeberl M. R. , Douglass A. R. , Stolarski R. S. , Woodbridge E. L. , Jonsson H. , Lait L. R. , Newman P. A. , Proffitt M. H. , Anderson D. E. , Loewenstein M. , Chan K. R. , Webster C. R. , May R. D. , Kelly K. K.
Published: February 2008

In situ measurements of NO and NOy are used to derive the ratio NOx/NOy along the flight track of the NASA ER‐2 aircraft. Data are presented for two flights at mid‐latitudes in October 1991 during the Airborne Arctic Stratospheric Expedition‐II (AASE‐II). Aerosol particle surface area was concurrently measured. The observations are compared with a photochemical model integrated along back trajectories from the aircraft flight track. Comparison of observations with the model run along trajectories and at a fixed position clearly and quantitatively demonstrates the importance of an air parcel's dynamic history in interpretation of local chemical observations. Comparison of the data with model runs under different assumptions regarding heterogeneous chemistry further reinforces the case for occurrence of the reaction of N2O5 + H2O on sulfate aerosol surfaces in the atmosphere. Finally, comparisons for which relative changes in the model and the data are not consistent caution that our ability to resolve all the observations is not yet complete.
Rate constant for the reaction of OH with CH3CCl2F (HCFC‐141b) determined by relative rate measurements with CH4 and CH3CCl3
Authors: Huder Karin , DeMore William B.
Published: February 2008

Determination of accurate rate constants for OH abstraction is of great importance for the calculation of lifetimes for HCFCs and their impact on the atmosphere. For HCFC‐141b there has been some disagreement in the literature for absolute measurements of this rate constant. In the present work rate constant ratios for HCFC‐141b were measured at atmospheric pressure in the temperature range of 298–358K, with CH4 and CH3CCl3 as reference gases. Ozone was photolyzed at 254 nm in the presence of water vapor to produce OH radicals. Relative depletions of 141b and the reference gases were measured by FTIR. Arrhenius expressions for 141b were derived from each reference gas and found to be in good agreement with each other. The combined expression for HCFC‐141b which we recommend is 1.4×10−12 exp(−1630/T) with k at 298 K being 5.9×10−15 cm³/molec‐s. This value is in excellent agreement with the JPL 92–20 recommendation.
Seismicity and tremor in a submarine hydrothermal field: the northern Juan De Fuca Ridge
Authors: McClain J. S. , Begnaud M. L. , Wright M. A. , Fondrk J. , Von Damm G. K.
Published: February 2008

We have made the first multi‐year deployments of a small number of ocean bottom seismometers on a mid‐ocean ridge. We located our instruments in and around a vigorous hydrothermal vent field on the Endeavour Segment of the Juan de Fuca Ridge. The deployments have revealed a consistent pattern of activity comprising several types of events. Most abundant are swarms of extremely small microearthquakes that we suggest are associated with cracking of the oceanic crust. We also observe local tectonic earthquakes that occur about four times per day. Preliminary hypocentral locations place these tectonic events away from the ridge axis and outside the hydrothermal field. The seismicity on the Endeavour Segment is remarkably different from the southern Juan de Fuca Ridge where little, if any, tectonic activity is occurring. We speculate that the Endeavour and southern Juan de Fuca Ridge are in two different phases of their long‐term evolution. The latter has only rare activity that is only beginning to focus hydrothermal circulation along faults. In contrast, the Endeavour Segment is in an active tectonic phase; and the faults have had time to develop robust hydrothermal circulation, resulting in large hydrothermal vent deposits.
Quantifying the distribution and transport of pelagic sediments on young abyssal hills
Authors: Webb Helen F. , Jordan Thomas H.
Published: February 2008

The post‐depositional transport of pelagic sediments on rough seafloor is approximated as a nonlinear diffusive process. The topographic slope distribution of the sediment‐water interface depends primarily on the apparent sediment diffusivity κ, the average sediment load L, and the root‐mean‐square height of the abyssal‐hill basement H. These parameters have been determined for the ARSRP corridor on the west flank of the Mid‐Atlantic Ridge by fitting theoretical models to the slope distribution observed from center‐beam Hydrosweep data. The average value of the apparent diffusivity is

. H varies between 188 and 285 m, with a mean of 230 ± 7 m. L is estimated to be as thin as 10 m on 5‐Ma crust near the ridge crest, thickening to values greater than 50 m at 10‐15 Ma and then decreasing to less than 30 m on 25‐Ma crust in the western portion of the corridor. The decrease in sediment load with age may be associated with a shallower carbonate compensation depth prior to the late Miocene.
Broadband bearing‐time records of three‐component seismic array data and their application to the study of local earthquake coda
Authors: Wagner Gregory S. , Owens Thomas J.
Published: February 2008

High‐frequency three‐component array data are used to study thePandScoda produced by local earthquakes. The data are displayed as broadband bearing‐time records which allow us to examine a complete time history of the propagation directions and arrival times of direct and scattered phases crossing the array. This visualization technique is used to examine the wavefield on two scale lengths using two sub‐arrays of sensors. Results suggest thatPcoda is dominated byPenergy propagating sub‐parallel to the diectParrival. TheScoda propagates in all directions and appears to be composed predominantly ofSand/or surface wave energy. Significantly moreScoda appears on the smaller scale length sub‐array relative to the larger scale array suggesting that much of theScoda remains coherent for only very short distances.
Overlapping rift‐zone segments and the evolution of the South Iceland Seismic Zone
Authors: Gudmundsson Agust , Brynjolfsson Sigurdur
Published: February 2008

The South Iceland seismic zone is a 20–60 km‐wide (north‐south) and up to 70 km‐long zone of north and north‐northeast trending Holocene arrays of en echelon tension fractures. These fracture arrays are related to dextral strike‐slip faults buried by Holocene lava flows. In this zone, major destructive earthquake sequences occur at intervals of 45–112 years, the largest events reaching magnitude 7 (Ms). We propose that this seismic zone is located between overlapping rift‐zone segments (spreading centers), where the eastern segment has been propagating to the south during the past 3 Ma. We made a finite element study of this configuration with the segments modeled as mode I cracks loaded in tension. The results suggest that the South Iceland seismic zone in general, and the north and north‐northeast trending dextral faults in particular, develop in response to the shear stresses generated between the rift‐zone segments.
Simultaneous observations of subauroral electron temperature enhancements and electromagnetic ion cyclotron waves
Authors: Erlandson R. E. , Aggson T. L. , Hogey W. R. , Slavin J. A.
Published: February 2008

Observational results from an investigation of low frequency (0.5–4.0 Hz) electromagnetic ion cyclotron waves and subauroral electron temperature enhancements recorded from the DE‐2 satellite are presented. Four different wave events were analyzed, all recorded at magnetic latitudes from 57–60°, magnetic local times from 8–14 hours, and altitudes from 600–900 km. The peak wave amplitudes during the events ranged from 8–70 nT and 5–30 mV/m in the magnetic and electric field, respectively. Electron temperature (Te) enhancements at the time of the waves were observed in 3 of 4 events. A linear relationship between the wave magnetic field spectral density and Te enhancements was found for these events. The Te enhancements were also correlated with an enhanced flux of low energy electrons. During one event (82104) an enhanced flux of electrons were observed at energies up to 50eV and at nearly all pitch angles, although the flux was largest in the precipitating and upflowing directions. It is suggested that the waves are responsible for heating the low energy electrons which precipitate to the ionosphere and produce the observed Te enhancements. The upflowing electron population appears to be heated at ionospheric altitudes, below the DE‐2 satellite. The precipitating electrons may also be heated at ionospheric altitudes through Landau damping, although the observations do not rule out electron heating near the equator.
Generation of waves in the Venus mantle by the ion acoustic beam instability
Authors: Huba J. D.
Published: February 2008

The ion acoustic beam instability is suggested as a mechanism to produce wave turbulence observed in the Venus mantle at frequencies 100 Hz and 730 Hz. The plasma is assumed to consist of a stationary, cold O+ ion plasma and a flowing, shocked solar wind plasma. The O+ ions appear as a beam relative to the flowing ionosheath plasma which provides the free energy to drive the instability. The plasma is driven unstable by inverse electron Landau damping of an ion acoustic wave associated with the cold, ionospheric O+ ions. The instability can directly generate the observed 100 Hz waves in the Venus mantle, as well as the observed 730 Hz waves through the Doppler shift of the frequency caused by the satellite motion.
Coherence lengths of upstream ULF waves: Dual ISEE observations
Authors: Le G. , Russell C. T. , Orlowski D. S.
Published: February 2008

Waves are generated in front of planetary bow shocks by a variety of plasma instabilities and they occur over a wide range of frequencies and wavelengths. In the strongly Doppler shifting environment of solar wind, multiple spacecraft observations are needed to determine unambiguously the wave properties such as frequency, phase velocity, and wavelength. The separations of the spacecraft required for these studies are restricted because the waves have finite coherence lengths. The multiple spacecraft must be located within a coherence length of each other in order that they are studying the same wave. In this study, we have used high time resolution simultaneous magnetic field data from the dual ISEE spacecraft to study the coherence lengths of upstream ULF waves. We examine the cross‐correlation between ISEE 1 and 2 observations for different spacecraft separations and determine the coherence lengths for upstream 30‐second waves, 3‐second waves and one‐Hz waves. We find that the observed coherence lengths are consistent with those estimated from the bandwidth of the spectral peak, and that these lengths vary markedly from less than 100 km to over 1 RE. In order to study all these wave phenomena, a multiple spacecraft mission such as the upcoming ESA Cluster mission would need to be capable of assuming a wide variety of possible separations.
Thermal convection in lava lakes
Authors: Davaille Anne , Jaupart Claude
Published: February 2008

In magma reservoirs, large temperature contrasts imply large variations of viscosity. We determine the characteristics of thermal convection in the laboratory for viscosity ratios of up to 106. In a fluid layer cooled from the top, convection develops below a stagnant lid. Plumes generate temperature fluctuations whose magnitude, θmax, is proportional to the temperature contrast across the unstable region, ΔTe. Scaling analysis and experimental data show that both temperature scales depend solely on the local function describing the variation of viscosity µ at temperatures close to that of the layer interior, Tm, and are equal to: In the Makaopuhi lava lake (Hawaii), temperature fluctuations were recorded below the growing crust. For the viscosity function of the Makaopuhi magma, their magnitude is predicted to be 18°C, in agreement with the observations.
A new formalism for inferring mantle viscosity based on estimates of post glacial decay Times: Application to RSL variations in N.E. Hudson Bay
Authors: Mitrovica J. X. , Peltier W. R.
Published: February 2008

We outline a new parameterization which, when applied to RSL curves for sites within previously glaciated regions, yields a data set which is insensitive to details of the ice loading history over the region. The parameterization recognizes the exponential‐like form of the RSL histories in such regions, and it provides a set of estimates for the characteristic decay time of that form. These estimates permit robust inferences of mantle viscosity below previously glaciated regions which are relatively unbiased by assumptions regarding the details of the surface ice cover. We apply the new parameterization to a small set of oft‐studied RSL curves in N.E. Hudson Bay. Using forward and inverse analyses of the decay time estimates we derive constraints on the radial profile of mantle viscosity below the region, and assess a set of previously proposed models for the viscosity profile below the area.