bluuebunny/crossref_metadata_2025 huggingface dataset:
Telemetry interference incorrectly interpreted as evidence for lightning and present‐day volcanism at Venus
Authors: Taylor Harry A. , Cloutier Paul A.
Published: February 2008

Spike‐like responses to interruptions in the data recorded by the Orbiter Electric Field Detector (OEFD) on the Pioneer Venus Orbiter (PVO) have been incorrectly identified as broadband whistler noise and then interpreted as evidence of lightning and volcanism by Singh and Russell [1986; 1987]. We show that these spikes are non‐physical artifacts of the processing of interruptions in telemetry data and are readily distinguished from other non‐artificial noise appearing in the measurements. We independently analyze the spikes and the non‐artificial noise to show that key portions of the results of Singh and Russell are compromised by the inclusion of the artificial data. This conclusion is certified by the fact that (a) the distribution of the spikes‐only data matches the distribution of noise presented by Singh and Russell, while (b) the number and distribution of all non‐spike noise is quite incompatible with their results. This finding is consistent with our prior research, and leads us to reiterate that the PVO electric field data set used by Singh and Russell provides no basis for inferring the presence of either lightning or present‐day volcanism at Venus.
Heterogeneous reactions of N2O5 with H2O and HCl on ice surfaces: Implications for Antarctic ozone depletion
Authors: Leu Ming‐Taun
Published: February 2008

Laboratory studies of heterogeneous reactions of N2O5 with H2O and HCl on ice surfaces have been performed in a fast flow reactor. A differentially pumped quadrupole mass spectrometer with an electron impact ionizer was used as a detector for the trace gas analysis. The reaction probability (or the heterogeneous reaction rate) of N2O5 on water ice was measured to be 0.028 (±0.011) at 195 K, while nitric acid was the sole product in the condensed phase. This reaction may effectively provide a sink for odd nitrogen species during the polar winter. In the presence of HCl with mole fractions between 0.015 and 0.04 in ice, the measured reaction probability of N2O5 was enhanced by about a factor of 2 at 195 K while nitryl chloride (ClNO2) or chlorine nitrite (ClONO) was found to be the major product in the gas phase. The quoted error bar represents the statistical error only. ClNO2 or ClONO can be readily photolyzed in the austral spring to form active chlorine which removes stratospheric ozone through several catalytic cycles. Another reaction product was nitric acid which remained in the solid phase. Since the polar stratospheric clouds are thought to consist of ice particles or possibly mixtures of HCl‐ice on the surface, the large reaction probabilities measured in this work suggest that these reactions should be a major factor in producing the observed springtime ozone depletion in the Antarctic stratosphere. Finally, a new ozone destruction mechanism based on surface recombination of ClO radicals is also proposed.
The Cajon Pass Scientific Drilling Experiment: Overview of phase 1
Authors: Zoback Mark D. , Silver Leon T. , Henyey Thomas , Thatcher Wayne
Published: February 2008

The Cajon Pass Scientific Drilling Project is a broad, interdisciplinary experiment involving over two dozen principal scientists. Phase I of drilling, coring and downhole experimentation began Dec. 8, 1986 and ended April 2, 1987 with the hole at a depth of 2115 m, 82 m of core recovered and a wide range of downhole experiments successfully completed. In this paper we briefly outline the scientific motivation for the project and provide an overview of the scientific program. We also indicate some of the varied research areas in the earth sciences where data obtained in this experiment will provide unique and important insight into active in situ processes, regional geologic structure, and rock and fluid composition and origin.
Geologic setting and lithologic column of the Cajon Pass Deep Drillhole
Authors: Silver Leon T. , James Eric W.
Published: February 2008

The Cajon Pass Deep Drillhole penetrates a late Tertiary basin developed on crystalline basement in the SW Mojave Desert, 4 km from the San Andreas fault. Cores, continuous cuttings and geophysical logs from phase I show great diversity in rock types, structure, and alteration. The hole encountered Cajon formation arkoses; granodiorite/tonalite; unusual megacrystic granite and augen gneiss; granitic and pelitic gneisses with quartzite; quartzofeldspathic orthogneiss cut by sheets of hornblende gabbro; and interlayered mafic and quartzofeldspathic orthogneisses with rare calcsilicate intervals. Foliation and compositional layering have low dips throughout the column and layered gneisses contain 10‐cm‐scale recumbent folds. Faults and alteration zones bound several rock units with low apparent dips. Basement cores are typically cut by steep fractures, <1 mm wide, that contain zeolites±calcite or chlorite‐epidote. Fractures and faults decrease in abundance with depth.
Rheological control of Wadati‐Benioff zone seismicity
Authors: Brodholt John , Stein Seth
Published: February 2008

Intermediate and deep focus earthquakes in Wadati‐Benioff zones are thought to occur in the cold interiors of downgoing slabs which are significantly stronger than the warmer mantle. Given that earthquakes in oceanic lithosphere appear restricted by an isotherm, and hence a given value of lithospheric strength, we investigate whether a similar formulation is useful for subducting plates. Strength in downgoing slabs should be affected by both pressure and temperature, an effect previously treated using a depth‐dependent limiting temperature for seismicity [Wortel, 1982]. We find this limiting temperature implies that a possible limiting strength increases strongly with depth, unless either the temperatures were too low or the activation volume too large. Comparison of the analytic model used by Wortel with numerical thermal models appears to exclude the first possibility. We explore the second possibility by using the numerical thermal model to compute strength contours for flow law constants reported from laboratory experiments, and find that the expected pressure strengthening is large enough that the slab should have considerable strength well below the deepest seismicity. We conclude that if laboratory results are applicable to these conditions, either a strongly depth‐dependent limiting strength exists or factors in addition to strength control the distribution of subduction zone earthquakes.
Circulation from a joint gravity field solution determination of the general ocean
Authors: Tapley B. D. , Nerem R. S. , Shum C. K. , Ries J. C. , Yuan D. N.
Published: February 2008

With the development of satellite altimetry, it is possible to infer the geostrophic velocity of the surface ocean currents, if the geoid and the position of the satellite are known accurately. Errors in current geoid models and orbit computations, both due primarily to errors in the Earth's gravity field model, have limited the use of altimeter data for this purpose. The objective of this investigation is to demonstrate that altimeter data can be used in a joint solution to simultaneously estimate the quasi‐stationary sea surface topography, ζ, and the model for the gravity field. Satellite tracking data from twelve satellites were used along with Seasat altimeter data for the solution. The estimated model of ζ compares well at long wavelengths with the hydrographic model of ζ. Covariance analysis indicates that the geoid is separable from ζ up to degree 9, at which point geoid error is comparable to the signal of ζ.
Observations of sodium in the tenuous lunar atmosphere
Authors: Tyler Ann L. , Kozlowski Richard W. H. , Hunten Donald M.
Published: February 2008

Spectra showing the sodium D lines above the Moon's bright limb (subsolar point) were obtained at first and last quarters, May 27 and June 7, 1988. The number density at the surface is 57 ± 20 atoms cm−3 and the scale height is 79 ± 8 km, compatible with the temperature of the surface. Comparison with the Mercurian density of 2.6×104 atoms cm−3 reveals an enigma. Despite the apparent general similarity of the surfaces, the sodium densities are in a ratio of ∼ 400. The difference may be attributed to differences in source or loss mechanisms or to some fundamental compositional difference between the two planets. The possibility that the source is rapid diffusion of sodium through Mercury's crust and regolith is discussed as well as recent observational evidence that Mercury's regolith is of intermediate rock type and may be more sodium‐rich than the Moon's.
Source of bursty radio emissions from Uranus
Authors: Buti B. , Lakhina G. S.
Published: February 2008

The distribution of energetic electrons on the auroral field lines in the magnetosphere of Uranus can develop large anisotropies and a large loss cone. These, in turn, can lead to large‐amplitude whistler waves and upper‐hybrid waves. Nonlinear currents caused by interaction between these waves can produce radio emissions that are in good agreement with the bursty Uranian kilometric radiation observed by Voyager 2.
An event of distinct ion polar rain
Authors: Newell Patrick T. , Meng Ching ‐I.
Published: February 2008

Although the comparatively featureless polarcap precipitation phenomenon of the electron polar rain has been known and studied since the work of Winningham and Heikkila [1974], to date there has been almost no work concerning ion polar rain, apparently because of its low intensity. This report documents a clear instance of ions at magnetosheath energy levels, precipitating in the manner characteristic of polar rain at flux levels of ⪍ 109 eV/cm² ‐s‐ sr—a flux about 10 times larger than that reported in the only previously published discussion of ion polar rain [Hardy et al., 1986]. A Maxwellian distribution with a temperature of 230 eV and a density of 0.02/cm³ fits the ion polar rain reasonably well. The comparatively high intensity permits verification that the strong dayside‐nightside gradient expected and observed in electron polar rain also occurs in the ion polar rain, and that the sign of the dawn‐dusk gradient was appropriate for the IMF By component at the time. A fairly typical (somewhat intense) electron polar rain accompanied the ion polar‐cap precipitation, displaying the same gradients as the ions.
Groundwater flow records indicating earthquake occurrence and induced Earth's free oscillations
Authors: Kawabe Iwao , Ohno Ichiro , Nadano Shinji
Published: February 2008

Significant changes in groundwater flow were observed immediately before and after an earthquake with M=6.6 occurred on March 18, 1987, in southwest Japan. The groundwater flow from a deep borehole well 226‐km northeast of the epicenter had begun to increase slightly 15 minutes before the earthquake. Just after the shock, the flow rate increased rapidly and exponentially approached a constant, but there were still oscillatory fluctuations even 5 hours later. The fluctuations correspond to 0S2 and 0S3 spheroidal modes of free oscillations of the earth. The non‐oscillatory transient flow must be the response to the residual field and/or to some non‐recoverable deformation of the groundwater reservoir resulting from strong ground motions due to seismic waves caused by the earthquake. Fault model calculations, however, indicate that the residual strain effect on the transient flow change is unimportant. The preseismic flow increase indicates a change in regional stress field preceding the earthquake. The present observations illustrate that groundwater responds systematically to minute crustal deformations just before and after an earthquake.
Fluid percolation through single fractures
Authors: Pyrak‐Nolte Laura J. , Cook Neville G. W. , Nolte David D.
Published: February 2008

Large deviations from "cubic‐law" dependence of laminar fluid flow through fractures on the apparent mechanical aperture of a fracture can be explained by assuming: 1) cubic‐law dependence of flow on the actual local aperture at the microscopic level; 2) conservation of rock volume when deforming the fracture; and 3) macroscopic flow properties are dominated by the critical neck (the smallest aperture along the path of highest aperture through the fracture).
VHF radar measurements of momentum flux in the summer polar mesosphere over Andenes (69°N,16°E), Norway
Authors: Reid Iain M. , Rüster Rüdiger , Czechowsky Peter , Schmidt Gerhardt
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 upward flux of horizontal momentum per unit mass
associated with gravity waves and turbulence near the summer polar mesopause. Here we describe the experiment and present some preliminary results. When averaged over a period of about three hours, magnitudes of
are found to reach a maximum value of 66 m² s−2 near the peak of the so‐called Polar Mesopause Summer Echo (PMSE). The PMSE itself appears to exhibit substantial aspect sensitivity.
Ozone reduction in the 1980's: A model simulation of anthropogenic and solar perturbations
Authors: Brasseur Guy , Hitchman Matthew H. , Simon Paul C. , De Rudder Anne
Published: February 2008

An interpretation of global ozone changes deduced from satellite data obtained since 1979 is presented, based on two‐dimensional model simulations. The study shows that a depletion in total ozone of the order of 2 percent and a reduction in ozone density near 40 km of 7 to 12 percent over the 1979–1986 period are consistent with the observed increase in trace gas densities (chlorofluorocarbons, methane, nitrous oxide, carbon dioxide) and the simultaneous decrease in solar activity during this period. The model also suggests that ozone variations of solar and anthropogenic origins between 1979 and 1986 were of similar magnitude but that the ozone response to trace gas emissions increases substantially with latitude while the solar signal in ozone is present lower in the atmosphere and is nearly independent of latitude.
The 1987 Antarctic Ozone Hole: A new record low
Authors: Krueger Arlin J. , Schoeberl Mark R. , Stolarski Richard S. , Sechrist Frank S.
Published: February 2008

In 1987 the Antarctic springtime total ozone as measured by TOMS was substantially lower than in any previous year. Polar ozone levels began decreasing significantly after a mesoscale transient minimum developed over the Weddell Sea on September 5–7. The total ozone over most of the Antarctic continent decreased to less than 200 DU on September 19, and a region where total ozone was less than 125 DU developed on September 30. The lowest level observed was 109 DU on October 5 near the South Pole, a value 29 DU less than the 1985 previous record low. Compared with previous years the 1987 October zonal mean total ozone is substantially lower poleward of 60°S. Antarctic total ozone in 1987 also showed the greatest rate of ozone decrease as well as the longest persistence of the ozone hole.
Multifractal analysis of resolution dependence in satellite imagery
Authors: Gabriel P. , Lovejoy S. , Schertzer D. , Austin G. L.
Published: February 2008

Augmenting a satellite's resolution reveals increasingly detailed structures that are found to occupy a decreasing fraction of the image, while simultaneously brightening to compensate. By systematically degrading the resolution of visible and infra red satellite cloud and surface data as well as radar rain data we define resolution‐independent co‐dimension functions that describe the spatial distribution of image features as well as the resolution dependence of the intensities themselves. The scale invariant functions so obtained fit into theoretically predicted universality classes. These multifractal techniques have implications for our ability to meaningfully estimate cloud brightness fraction, total cloud amount, as well as other remotely sensed quantities. A preliminary account of this work can be found in Gabriel et al., (1988a). See also Gabriel (1988).
Deuterium concentration and growth rate of Antarctic first‐year sea ice
Authors: Souchez Roland , Tison Jean‐Louis , Jouzel Jean
Published: February 2008

Deuterium concentration in congelation sea ice is dependent on the freezing rate. The growth rate can be determined using a box diffusion model where the initial sea water δD value is kept constant in the course of freezing outside a boundary layer developed close to the ice interface. For the boundary layer thickness estimated from Na concentration measurements, the model gives results in accordance with previous studies of sea ice growth rates.
Zinc partitioning in Mediterranean rainwater
Authors: Losno Rémi , Bergametti Gilles , Buat‐Ménard Patrick
Published: February 2008

Eleven rainwater samples were collected in the Western Mediterranean region in clean conditions in order to study the partitioning of zinc between soluble and insoluble forms. The pH of the rainwater sampled ranges between 4 and 7; the high values of pH resulting from the neutralization of acidic species by the calcium carbonate present in desertic dusts. The soluble zinc ranged between 15 and 99% of the total zinc; the higher percentage are observed for the lower pH, and the lower percentage for the higher pH. This variable solubility can be explained by an adsorption‐desorption equilibrium which is highly sensitive to the value of pH in rainwater.
A wandering Gondawanaland's impact on summer temperatures
Authors: Ledley Tamara Shapiro
Published: February 2008

The effect of the position of Gondawanaland on summer temperatures is examined with a coupled energy balance climate‐sea ice model that includes the ice‐albedo feedback. These temperatures are important in determining when ice‐free conditions can exist near the south pole. Results show that when the land mass is centered on the south pole summer temperatures are warmer than when the pole is located at the continental edge; however, this warming is moderated by the ice‐albedo feedback. In addition, results indicate that paleogeography influences the magnitude of moisture transport toward the pole, affecting the initiation of glaciation.
How well can we resolve the deep seismic slab with seismic tomography?
Authors: Zhou Hua‐wei
Published: February 2008

The three‐dimensional P and S velocity tomographic images around the Wadati‐Benioff zone under the island arcs of the northwest Pacific are analyzed. Estimations of resolution and error show that the fast seismic anomalies associated with the subduction zones are generally real and resolvable. The anomalies are slab‐like in most parts of the upper mantle, and become folded and broadened with depth. Near the bottom of the upper mantle, fingering of the slabs, including segmenting and shallow angle spreading, is indicated. The fingering under Japan and the Izu‐Bonin trench has a tendency to flatten to sub‐horizontal, while possible downward spreading is seen under parts of the Kuril trench.
No evidence of a new magmatic gas contribution to the Solfatara volcanic gases, during the Bradyseismic crisis at Campi Flegrei (Italy).
Authors: Tedesco D. , Pece R. , Sabroux J. C.
Published: February 2008

A volcano‐tectonic crisis with strong seismic activity and rapid uplift started in 1982, and continued until its abrupt disappearance at the beginning of 1985, at Campi Flegrei caldera (Southern Italy). The chemical composition of the fumarolic fluids has been recorded during the last five years and, from geochemical and thermodynamical considerations, it has been deduced that the shallow reservoir feeding the fumaroles remained chemically isolated, at least with respect to major magmatic components, from the magma chamber inferred to be located at depth.
Constraints on locations of large intraplate earthquakes in the Northern Territory, Australia from observations at the Warramunga seismic array
Authors: Bowman J. Roger
Published: February 2008

Three earthquakes of Ms 6.3, 6.4 and 6.7 near Tennant Creek, Northern Territory, Australia on January 22, 1988 produced 35 km of surface rupture in the Precambrian shield. The surface deformation consists of low‐angle (20°‐30°) thrust faulting on 2 main scarps separated by a 7 km gap. The Kunayungku (western) fault and the eastern end of the Lake Surprise (eastern) fault dip to the south, while the western end of the Lake Surprise fault dips to the north. Although these earthquakes are among the largest ever recorded on the Australian continent, there is no record of earthquakes larger than magnitude 5 within 500 km prior to 1987. Data from the Warramunga (WRA) seismic array located 30 km east of the rupture show no local activity between 1965 and 1986. Two small events in the fault area were observed in February, 1986 and were followed by a series of 6 mb 4 to 5.2 earthquakes in January, 1987 and their aftershocks. The 1986, 1987 and January 22, 1988 mainshocks all nucleated within a zone about 5 km across from north to south, but elongated radially away from WRA by up to 30 km. Although the distribution of these events is in the direction of poorest hypocentral resolution, we can place meaningful constraints on the epicenters by examining the range of solutions that fit the P arrival time data. The 1986 and largest 1987 events were restricted to the western part of the fault zone. The three mainshocks progressed from west to east suggesting that the Kunayungku scarp was produced by the first mainshock, and the west and east ends of the Lake Surprise scarp by the second and third, respectively.
Unusual earthquakes in the Gulf of Alaska and fragmentation of the Pacific Plate
Authors: Lahr J. C. , Page R. A. , Stephens C. D. , Christensen D. H.
Published: February 2008

Two recent Ms 7.6 strike‐slip earthquakes in the northern Gulf of Alaska ruptured a composite 250‐km‐long north‐striking zone in the Pacific plate. These shocks are attributed to a combination of enhanced tensional stress in the Pacific plate seaward of and following the great (Mw 9.2) Alaska earthquake of 1964, and compressional stress resulting from collision of the Yakutat terrane with North America. The occurrence of these shocks reflects fragmentation of the northeast corner of the Pacific plate, possibly the initial step in establishing a new plate boundary seaward of the current boundary.
Nonlinear evolution of high frequency R‐mode waves excited by water group ions near comets: Computer experiments
Authors: Kojima H. , Matsumoto H. , Omura Y. , Tsurutani B. T.
Published: February 2008

An ion beam resonates with R‐mode waves at two frequency bands. These are a high frequency RH mode (ω » Ωp) and a low frequency RL mode (ω ∼ ΩH2O+), where Ωp and ΩH2O+ are cyclotron frequencies of protons and water ions, respectively. We study the nonlinear evolution of beam‐generated RH waves by one‐dimensional hybrid computer experiments. Both wave‐particle and subsequent wave‐;wave interactions are examined. We find that the RH waves through the interaction with an ion beam formed by pick‐up heavy ions near comets, grow to a level of Bw/Bo ∼ 0.23. The waves saturate by wave‐wave interactions (via the decay instability) supplying energy to backward travelling daughter R‐mode waves with slightly lower k (and hence lower ω) as well as forward travelling longitudinal waves. The backward travelling daughter R‐mode waves decay further to granddaughter waves with still lower k. We show that this inverse cascading process occurs faster than the growth of the RL mode instability and produces a wide band wave spectrum which extends from the wavenumber of beam‐excited RH mode to much lower k. The nonlinearly excited longitudinal sound waves play a role in heating solar wind protons.
Noble gases in silica and their implication for the terrestrial “missing” Xe
Authors: Matsuda Jun‐ichi , Matsubara Kayo
Published: February 2008

Elemental abundances of noble gases in siliceous microfossils from deep‐sea sediments were determined employing the stepwise heating technique. Almost all the Ar and about 80% of the total Kr were released in the lowest temperature fraction of 800°C. Only Xe was released in higher temperature fractions, suggesting that Xe was tightly trapped inside silica. The Xe concentrations of siliceous microfossils seem to lie on the correlation line of Xe content vs. the temperature of geothermal water obtained for amorphous silica of geothermal origin. The selective trapping of Xe at high temperatures in amorphous silica indicated the possibility that amorphous silica is the reservoir of the terrestrial "missing" Xe. However, quantitative calculation showed that the total amount of Xe in amorphous silica could be at most only 5‐20 % of the total "missing" Xe.
Impact of heterogeneous reactions on stratospheric chemistry of the Arctic
Authors: Douglass Anne R. , Stolarski Richard S.
Published: February 2008

The possible depletion of ozone due to heterogeneous reactions occuring in Arctic polar stratospheric clouds (PSC's) is fundamentally different from the Antarctic situation. PSC's in the Arctic are relatively short‐lived and occur over limited regions of the Arctic stratosphere. We have examined the Arctic situation using a model which calculates photochemical processes as a function of longitude in air circulating with fixed velocity around the pole at fixed pressure level and latitude. The model allows sunlight to vary diurnally and PSC's to occur in specified subregions of the domain. Measurements of chemical species including HCl, ClO, NO2 and HNO3 downwind from a PSC should show obvious changes compared to measurements in air unaffected by clouds. These species concentrations are found to be sensitive to sticking coefficients, cloud characteristics including particle number density and surface area, and to the PSC exposure time.
Observation of mirror waves downstream of a quasi‐perpendicular shock
Authors: Hubert D. , Perche C. , Harvey C. C. , Lacombe C. , Russell C. T.
Published: February 2008

We have performed auto and cross spectral analysis of the electron density and vector magnetic field fluctuations recorded aboard ISEE 1 and 2 in the magnetosheath close to the Earth's bow shock when in quasi‐perpendicular configuration. The analysis shows the characteristic signatures of mirror type modes downstream of the undershoot of the shock.
Seismic anisotropy of the inner core
Authors: Sayers Colin M.
Published: February 2008

Recent studies of seismic travel times and free oscillations have been interpreted in terms of an anisotropic inner core with cylindrical symmetry aligned with the earth's axis of rotation. The inner core is believed to consist of hexagonal close‐packed (hcp) iron. In this letter the velocity anisotropy is used to determine the coefficients Wlmn of a series expansion of the crystallite orientation distribution function in generalised spherical harmonics. This function gives the probability of a crystallite having a given orientation with respect to a set of axes fixed in the core. The solution to this problem enables construction of crystallographic pole figures, which suggest a strong alignment of hcp Fe c‐axes along the earth's axis of rotation.
The moments of inertia of Mars
Authors: Bills Bruce G.
Published: February 2008

The mean moment of inertia of Mars is, at present, very poorly constrained. The generally accepted value of 0.365 MR² is obtained by assuming that the observed second degree gravity field can be decomposed into a hydrostatic oblate spheroid and a nonhydrostatic prolate spheroid with an equatorial axis of symmetry. An alternative decomposition is advocated in the present analysis. If the nonhydrostatic component is a maximally triaxial ellipsoid (intermediate moment exactly midway between greatest and least) the hydrostatic component is consistent with a mean moment of 0.345 MR². The plausibility of this decomposition is supported by statistical arguments and comparison with the Earth, Moon and Venus. If confirmed, this new value would have significant implications for the inferred composition and climatic history of Mars. The Mars Observer mission may help resolve this issue.
Moment of inertia of three‐dimensional models of the Earth
Authors: Tanimoto Toshiro
Published: February 2008

The axes of the maximum moment of inertia of recent three‐dimensional models of the Earth deviate from the rotation axis by about one degree. This is at least a few orders of magnitude larger than the observed deviation. Simple analysis shows that this is related to the size of the (l=2,m = 1) component of density variations in the upper mantle, where l is the angular degree and m is the order of the spherical harmonics. An analytical formula for the deviation of the maximum moment of inertia is derived, which involves a radial integration of the (l=2,m=1) component of density. It is proposed that a new Earth model should be derived using this constraint.
Effect of sharp lateral heterogeneity on the Earth's normal modes
Authors: Neele Filip , Lognonné Philippe , Romanowicz Barbara , Snieder Roel
Published: February 2008

When inverting normal mode data for global large‐scale lateral heterogeneity, possible biases due to small‐scale structure are commonly ignored. We conducted two experiments. In the first one, we calculated, with a recently developed first order scattering formalism, the effect of a simplified subduction zone model on the eigenfrequencies of the fundamental spheroidal mode branch. The frequency shifts induced by this single subduction zone appear to be smaller by only a factor of 3 to 4 than shifts observed on long‐period seismograms, or than shifts induced by existing models of global upper mantle inhomogeneity. The second experiment involved a model of a hot spot plume on the core mantle boundary. Solving the variational problem with many coupling terms included, we calculated the effect of such a plume on the amplitude of some low angular order modes. The results suggest an effect at least as large as that due to available large scale mantle models. It thus appears, that relatively small‐scale, sharp lateral structure in different depth ranges of the Earth may have an important effect on normal mode observations and that these effects may not be ignored in inversions of normal mode data.
Coseismic radon changes in groundwater
Authors: Wakita H. , Igarashi G. , Nakamura Y. , Sano Y. , Notsu K.
Published: February 2008

Coseismic changes in the radon concentration of groundwater were consistently observed at a sensitive observation station for all nearby earthquakes (100–130 km away) with magnitudes of 6.0 and over, and for some earthquakes of the same magnitudes occurring up to about 400 km away. A total of 11 coseismic changes, larger than 2σ of the noise level, were observed for 16 earthquakes which occurred during the observation period, between January 1984 and July 1988. A similar change was also found for an M7.9 earthquake at a distance of about 1000 km. The radon changes lasted a few days in most cases; they may be caused by changes in the earth's stress field.
Gravity change caused by a fissure eruption
Authors: Okubo Shuhei , Watanabe Hidefumi
Published: February 2008

A simple relation holds between the gravity and elevation changes associated with a fissure eruption. If combined with inversion schemes, it enables us to estimate the location and geometry of the subsurface fractured area. We applied the technique to the 1986 eruption of the Izu‐Oshima volcano, Japan, where a textbook‐like fissure eruption was observed.
Detection of 17.5‐day period meridional current oscillations in the equatorial western Pacific Ocean during 1985
Authors: Halpern David
Published: February 2008

The first long term, near equatorial, near surface moored current measurements recorded in the Pacific Ocean west of 160°W were made at 0°, 150°E during 2 August 1985–1 February 1986. These data revealed 17.5‐day period oscillations of the meridional current. Prior to these measurements, these waves had only been observed eastward of about 165°W, which also was the westernmost extent of their appearance in ocean general circulation model simulations. The 17.5‐day period waves also occurred in simultaneous current measurements at 140°W, where the wave amplitude was 3 times greater. At both sites the 17.5‐day period wave amplitude was more than 50% of the record‐length standard deviations of the meridional current component. A wider spectral bandwidth and a smaller tendency towards rectilinear motion occurred at 150°E than at 140°W.
The solar tides and the Sun‐synchronism of satellite altimetry
Authors: Mazzega P.
Published: February 2008

Several days separate the consecutive overflights of a fixed geographical point by a geodesic satellite along the same track so that the semi‐diurnal and diurnal oceanic tides as measured by an on‐board altimeter will appear as low frequency oscillations of the ocean surface. This was an argument against the sun‐synchronous satellite altimeters for the study of (luni‐) solar tides, these constituents being rejected under the 2 cy/year frequency or even in the steady sea surface. However, this simplified scheme should be drastically modified by the adjunction of supplementary informations supplied by other data (e.g. from tide gauges), hydrodynamical models or statistics. Here we only show that using the a priori spatial statistical properties of the tides in a total inversion of altimeter data, the sun‐synchronous satellites may contribute to map the (luni‐) solar tides. In particular the accuracy of a tidal inverse solution is little dependent on its apparent frequency and on the proximity of the other aliased tides.
A new means for observation of small comets and other water‐laden bodies entering Earth's upper atmosphere
Authors: Banks Peter M.
Published: February 2008

This paper shows that the infrared radiance of comet‐associated water vapor clouds described by Frank et al. (1986b) is large relative to natural background emissions. This IR emission arises from scattering of solar radiation and earthshine and from excitation by upper atmospheric atomic oxygen. As a consequence, observations in space or from high‐altitude platforms should provide an unambigious signature of the entry of such objects into Earth's atmosphere.
Toroidal flow in the outer core and the thermal regime below the core‐mantle boundary
Authors: Olson Peter
Published: February 2008

Numerical calculations of fluid dynamos are used to constrain the probable origin of toroidal flows in the outer core. Azimuthal drift of the core fluid relative to the mantle is the sum of three components: (1) uniform differential rotation of the core relative to the mantle produced by electromagnetic torques on the mantle; (2) cylindrical flow driven by electromagnetic torques in the core, and (3) buoyantly driven thermal wind flow produced by lateral variations of temperature and composition. Dynamo calculations indicate that electromagnetic torques on the mantle contribute to long‐term drift, but are not likely to be its primary cause. Zonal flow driven by electromagnetic torques in the core and thermal wind flows driven by zonal temperature gradients are both sufficiently energetic to account for azimuthal flows with angular velocities of 0.1–0.5° yr−1, as inferred from frozen flux analyses of secular variation.
Compressible convection in the Earth's mantle: A comparison of different approaches
Authors: Steinbach Volker , Hansen Ulrich , Ebel Adolf
Published: February 2008

Numerical models of mantle convection using the Boussinesq, extended Bousinessq and anelastic‐liquid approximation are compared. For steady state solutions there is good quantitative agreement between the results if they are scaled in a proper way. Time‐dependent extended Boussinesq and anelastic‐liquid flows show only qualitative agreement, the main difference being a distortion of timescale. Compressibility induces an asymmetry in the structure of upper and lower boundary layers that cannot be observed in Boussinesq fluids.
Small‐wavelength geoid and topography anomalies in the South Atlantic Ocean: A clue to new hot‐spot tracks and lithospheric deformation
Authors: Fleitout Luce , Dalloubeix Christine , Moriceau Christophe
Published: February 2008

Numerous small‐wavelength elongated features are visible both on filtered geoid maps and on topography maps of the South Atlantic Ocean. A number of them are oriented along the directions of absolute plate motion between 80 Ma B.P. and 30 Ma B.P.: N50°E for the African plate and N63°W for the South American plate. Magmatic traces left over fixed convective plumes more numerous than the “classical” hot‐spots best explain these observations. Other traces, especially in the area of the Sandwich subduction zone and on the African plate are oriented in a N50°W direction and seem to indicate large‐scale deformation of the oceanic plates.
PcP amplitude calculations for a core‐mantle boundary with topography
Authors: Kampfmann W. , Müller G.
Published: February 2008

3D Kirchhoff theory is used to calculate synthetic short‐period (1 s) seismograms for the reflection PcP at the core‐mantle boundary (CMB). The CMB models have sinusoidal topography of wavelength L and amplitude E. E values of 0.5 and 1 km are assumed, in agreement with results of PKP‐precursor studies, and L ranges from 600 to 10 km. The corresponding PcP amplitude‐distance curves in the range 22–81° are compared with the smooth curve for a spherical CMB (E = 0). For L ≥ 100 km pronounced amplitude variations around the reference curve occur, corresponding to PcP focusing by lows and defocusing by highs of the CMB. For L ≤ 50 km the amplitude curve is smooth again, but with lower values than on the reference curve: part of the energy is deflected from the specular PcP ray of the reference model by diffuse reflection. These results are in qualitative agreement with seismological observations of (1) strong scatter in PcP amplitudes and (2) generally very low PcP amplitudes at distances beyond 70°
Inferring cloud deposition to a forest canopy using a passive cloudwater collector
Authors: Mueller Stephen F. , Imhoff Robert E.
Published: February 2008

A widely used passive cloudwater collector was operated continuously along with an automated canopy water throughfall measurement system at a high elevation spruce forest site. Cloudwater collection rate (Rc) and throughfall (TF) rate were examined to determine their interrelationship. In addition, the use of the cloudwater collector for inferring cloud liquid water content was examined. The degree of direct hourly correlation was fairly good between Rc and canopy TF rate for non‐rain periods when the canopy was saturated (the former explained 58% of the variance in the latter). The correlation was even better (R² = 0.84) when TF rate was time‐lagged one hour. Estimated liquid water content, using collector data, was characterized by a large degree of uncertainty. This uncertainty appears to be caused, to a large extent, by the inability of the estimation method to account for the variation in cloudwater collection efficiency as a function of wind speed and droplet size.
Gravity wave fluxes of O3 and OH at the nightside mesopause
Authors: Walterscheid R. L. , Schubert G.
Published: February 2008

A dynamical‐chemical model is used to determine concentration fluctuations, fluxes, mixing ratio fluxes, and flux divergences of the minor constituents OH, O3, HO2, H and O driven by gravity waves propagating through the nightside mesopause region. The model includes a five reaction chemical scheme for the production and loss of the minor species and the complete dynamics of linearized gravity waves in a motionless atmosphere. Wave fluxes of O3 and OH are small except for a 5 km thick region at about the level of the mesopause wherein the fluxes are large and downward. Wave‐induced transport of O3 and OH opposes diffusive down‐gradient transport of these species which would result in upward fluxes above ∼ 75 km for OH and above ∼ 81 km for O3, except for localized regions. Gravity wave fluxes of O3 can cause large changes in O3 number densities in times comparable to the O3 chemical time constant and they are therefore major contributors to the balance that determines O3 concentrations at the mesopause. Because of the short chemical time constant of OH, gravity wave fluxes of OH do not directly change OH concentrations. However, wave fluxes can alter OH concentrations indirectly through the modifications to O3 number densities and the rapid adjustment of OH to O3. By modulating the intensity and intrinsic frequency of gravity wave activity, tides can force diurnal and semidiurnal variations in the divergence of O3 and OH wave fluxes and in the concentrations or O3 and OH. Gravity wave fluxes are able to alter the mixing ratios of O3 and OH as a consequence of the chemistry. The coupling of wave dynamics and chemistry acts to reduce the mixing ratios of O3 and OH around 80 km.
Simultaneous observations of electrostatic oxygen cyclotron waves and ion conics
Authors: Kintner P. M. , Scales W. , Vago J. , Arnoldy R. , Garbe G. , Moore T.
Published: February 2008

A sounding rocket launched to 927 km apogee during an auroral substorm encountered regions of large quasistatic electric fields (≤ 400 mV/m), ion conics (up to 700 eV maximum observed energy) and fluctuating electric fields near the oxygen cyclotron frequency. Since the fluctuating electric fields frequently exhibited spectral peaks just above the local oxygen cyclotron frequency and since the fluctuating electric fields were linearly polarized, we identify them as electrostatic oxygen cyclotron waves (EOCW). The maximum amplitude of the EOCW was about 5 mV/m RMS. The EOCW closely correlated with the presence of ion conics. Because of the relatively low amplitude of the EOCW and their relatively low coherence, we cannot conclude that they are solely responsible for the production of the ion conics.
Seasonal variations of sea ice motion in the transpolar drift stream
Authors: Serreze Mark C. , McLaren Alfred S. , Barry Roger G.
Published: February 2008

Drifting buoy data for 1979–85 and meteorological fields for 1960–85 are used to assess sea ice motion in the Transpolar Drift Stream. Although the long‐term mean ice drift in this stream is toward the Fram Strait, three years (1979–81) with adequate drifting buoy data coverage show reversed ice motion over 30‐day periods in summer. This phenomenon is a response to seasonally changing wind forcing.
On the separation of relatively buoyant components from subducted lithosphere
Authors: Richards Mark A. , Davies Geoffrey F.
Published: February 2008

Subducted oceanic lithosphere consists of a sandwich of component layers (MORB underlain by depleted parent mantle). These layers give rise to intrinsic density contrasts within the slab which have been hypothesized to cause component separation after subduction. We explore this process through numerical models of simple layered slabs and through convection models which incorporate large, local chemical density contrasts. We show that the components of positive and negative buoyancy (density contrast × component volume) must be almost equal in order to cause significant component separation or to selectively block deep penetration of buoyant slab components in the transition zone. Published petrological constraints on component densities and relative volumes indicate that such buoyancy neutralization is not achieved in subducted slabs. Therefore, component separation should not occur on the timescale associated with the sinking of slabs through the upper mantle and transition zone.
Structure of slow magnetosonic shocks in low beta plasmas
Authors: Omidi N. , Winske D.
Published: February 2008

Slow magnetosonic shocks are an efficient way in which magnetic energy in a collisionless plasma is converted into particle flow and thermal energy. Previous analytic and simulation studies of slow shocks have suggested that their structure consists of a damped wavetrain beginning at the shock transition and extending into the downstream region. Spacecraft observations in the solar wind and the Earth's magnetotail have found structures that resemble slow shocks except that most of them do not possess a trailing wavetrain. To resolve the conflict between theory and observations of slow shocks, we have performed new simulations which correct some of the previous results and show that depending on the sonic Mach number and the ratio of electron to ion temperature, slow shocks may or may not possess a wavetrain.
Observation and interpretation of fast sub‐visual light pulses from the night sky
Authors: Nemzek R. J. , Winckler J. R.
Published: February 2008

Fast large aperture photometers directed at the zenith on clear nights near Minneapolis have recorded many light pulses in the millisecond time range, but aside from man‐made events these were almost entirely due to Rayleigh scattered distant lightning, with a residual very low rate (<0.1/hr) of unidentified pulses. We believe that 1 ms light pulses seen in several previous experiments (FAP's) may also be mostly Rayleigh scattered lightning, rather than fluorescent light due to electron precipitation from lightning‐induced whistlers as previously discussed.
Simultaneous radar and lidar observations of sporadic E and Na layers at Arecibo
Authors: Beatty Timothy J. , Collins Richard L. , Gardner Chester S. , Hostetler Chris A. , Sechrist Chalmers F. , Tepley Craig A.
Published: February 2008

During the early morning of January 16, 1989 the Arecibo 430 MHz incoherent scatter radar and the University of Illinois CEDAR Na lidar were operated simultaneously for several hours at the Arecibo Observatory, Puerto Rico (18°N, 67°W). At approximately 0425 LST a sporadic E (Es) layer began forming near 101 km altitude and moved steadily downward reaching an altitude of 99 km by 0500 LST. The electron abundance of the Es layer increased rapidly from approximately 3×109 cm−2 at 0510 LST to approximately 6×109 cm−2 by 0530 LST. During this same time period a sporadic Na (Nas) layer formed at the same altitude as the Es layer. Both the Es and Nas layers moved upwards together between 0530 and 0600 LST before dissipating at an altitude of 101 km. The high correlation between the altitude and abundance variations of the two layers strongly suggests that the Nas layer formation is related to the Es layer and may involve Na cluster ion chemistry.
S‐wave polarization inversion of the 15 October 1979, 23:19 Imperial Valley Aftershock: Evidence for anisotropy and a simple source mechanism
Authors: Zollo Aldo , Bernard Pascal
Published: February 2008

S polarizations from the 16 near source strong motion stations of the 15 October 1979, 23:19 Imperial Valley aftershock have been analyzed for constraining the source mechanism. They show a significant delay of the East component relative to the North component at most stations. Assuming that this is an effect of anisotropy with a horizontal symmetry axis in the upper 4 km of sediments (where the rays are dominantly vertical), the measured fast S polarizations are mainly oriented between N0°E and N25°E, and show a mean delay of 0.25 s between slow and fast S. This is consistent with an hexagonal anisotropy due to vertical cracks induced by the regional compressional stress field and parallel to it, with a mean fluid filled crack density of 0.1 to 0.2. The records, once corrected for the splitting effect, show S polarizations stable in time, which have been used to estimate the fault mechanism parameters. This is done by applying a new inversion method which is based on a model probability estimate. The error function is related to the polarization misfits, and the associated joint probability function of the data and parameter is computed in the whole model space. The inversion of the corrected S polarizations provides a unique and well constrained solution for the Imperial Valley aftershock mechanism (strike 145±5°, dip 85±10°, slip −155±15°), which is compatible with the available P polarities and is quite similar to the main shock mechanism.