bluuebunny/crossref_metadata_2025 huggingface dataset:
Cleopatra Crater on Venus: Venera 15/16 data and impact/volcanic origin controversy
Authors: Basilevsky A. T. , Ivanov B. A.
Published: February 2008

Cleopatra structure is a 100–km diameter feature having a morphology similar to that of double–ring basins of the Moon and Mercury and dissimilar to that of volcanic calderas on Mars, Earth, and Venus. The 2.4–km depth of Cleopatra is anomalously large compared to venusian and terrestrial impact craters of equivalent diameters. An impartial summary of the situation is as follows: if Cleopatra is a volcanic caldera, it is a strange caldera; if Cleopatra is an impact crater, it is a strange crater.
Major and Rare Gases at White Island Volcano, New Zealand: Origin and Flux of Volatiles
Authors: Marty Bernard , Giggenbach Werner F.
Published: February 2008

Analyses of fumarolic gases at White Island, New Zealand, are reported with special emphasis on rare gases (He, Ne, Ar, Kr and Xe). Normalization of major species to rare gases have lead to the identification of several sources: air‐saturated meteoric (or marine) water, a magma body, the crust and/or sediments. When compared to Mid Ocean Ridge discharges, the White Island gas discharge represents about 3%, 0.7%, 0.1% and 0.05% of the global water, carbon, sulfur and Helium‐3 discharges, respectively. This balance shows that, except for 3He which derives from the mantle, practically all rare gases, water and carbon, and part of sulfur, derive from originally superficial sources.
Nitric acid in polar stratospheric clouds: Similar temperature of nitric acid condensation and cloud formation
Authors: Pueschel Rudolf F. , Snetsinger Kenneth G. , Hamill Patrick , Goodman Jindra K. , McCormick M. Patrick
Published: February 2008

As shown independently by two different techniques, nitric acid aerosols and polar stratospheric clouds both form below similar threshold temperatures. This supports the idea that the polar stratospheric cloud (PSC) particles involved in chlorine activation and ozone depletion in the winter polar stratosphere are composed of nitric acid. One technique used to show this is inertial impaction of nitric acid aerosols using an ER‐2 aircraft; the other method is remote sensing of PSCs by the Stratospheric Aerosol Measurement (SAM II) satellite borne optical sensor. Both procedures were in operation during the Arctic Airborne Stratospheric Expedition in 1989, and the Airborne Antarctic Ozone Experiment in 1987. Analysis of Arctic particles gathered in situ indicates the presence of nitric acid below a “first appearance” temperature Tfa = 202 K. This is the same highest temperature a at which PSCs are seen by the SAM II satellite. In comparison, a “first appearance” temperature Tfa = 198 K was found for the Antarctic samples.
In situ measurements of NOx in the Airborne Arctic Stratospheric Expedition
Authors: Carroll Mary Anne , Montzka Denise D. , Hübler Gerhard , Kelly Kenneth K. , Gregory Gerald L.
Published: February 2008

In situ measurements of nitric oxide (NO) and nitrogen dioxide (NO2) were made simultaneously from the NASA DC‐8 aircraft as part of the Airborne Arctic Stratospheric Expedition. Mixing ratios of NOx (NO + NO2) were typically higher in the Arctic troposphere than in the stratosphere, with median values of 59 and 40 pptv, respectively. In the stratosphere, there tended to be a positive correlation between NOx and water vapor (H2O) and negative correlations between NOx and ozone (O3) and between NOx and total reactive odd‐nitrogen (NOy). The ratio of NOx to NOy, in conjunction with NOy, appears to be an excellent tracer of tropospheric or stratospheric air at northern latitudes during winter. Tropospheric NOx was typically 10 to 50% of gas‐phase NOy, while in the stratosphere, NOx was typically < 10%, and frequently <5% of gas‐phase NOy.
STARE observations of Pi 2 pulsations
Authors: Sutcliffe Peter R. , Nielsen Erling
Published: February 2008

The STARE radar system has for the first time been used to study Pi 2 pulsations associated with substorm onsets. Such pulsations have a period which typically makes them only marginally observable with STARE; nevertheless, an event has been identified. The spatial and temporal variations of the observed ionospheric flow vectors, and consequently also the electric field vectors, are complex and require further study, but are qualitatively comparable to model predictions. Magnetic field oscillations computed from the STARE data using the Biot‐Savart law correlate well with magnetometer data.
A seasonal budget of the Earth's axial angular momentum
Authors: Naito Isao , Kikuchi Naokichi
Published: February 2008

The seasonal variation of the earth's axial angular momentum budget is discussed with an error on the order of a few percent. The budget is based on the core‐mantle decoupling (CMD) hypothesis, using the length of day (LOD) data observed astronomically by the International Radio Interferometry Surveying and the atmospheric angular momentum data calculated from the forecast/analysis data set for numerical weather prediction of the Japan Meteorological Agency. The atmospheric relative angular momentum changes due to zonal wind account for an additional 23 % contribution over the annual budget. However, this is counterbalanced by the effects of the redistributions of air and water masses. Namely, about 16 % is accounted for by the redistribution of air mass, and remained about 7 % agrees with the contribution from surface water storage estimate on continents by Chao & O'Connor [1988]. These facts demonstrate a confirmation of the CMD hypothesis on time scale of a year. At the semi‐annual period, however, there still is a shortage of about 6 % in atmospheric and hydrospheric contributions to the budget.
Geophysical imaging with backpropagation and zeroth‐order phase approximation
Authors: Witten Alan , King Wendell C.
Published: February 2008

A promising technique for high resolution geophysical imaging has been proposed which is based on the inversion of an exact solution to the reduced wave equation. The method is known as backpropagation because it propagates a received waveform back into the host formation mapping wavespeed variations. The implementation of backpropagation is complicated by the fact that it requires a complete characterization of the wave source and the wave propagation properties of a homogeneous host medium. The imaging procedure can be simplified by utilizing a zeroth—order phase approximation which allows implementation with first arrival times. Numerical experiments and a field study suggest that this approach is a practical means for high resolution subsurface imaging.
Winter lightning along the East Coast
Authors: Orville Richard E.
Published: February 2008

More than 150,000 cloud‐to‐earth lightning flashes were recorded along the East Coast during the period 15 January–15 March 1986 in the region bounded by 25°N–40°N and 90°W–70°W. The majority of the flashes for the two month period occurred over the Atlantic Ocean in the vicinity of the Gulf Stream where a peak flash density of 0.7 flashes/km2 was observed approximately 270 km from the Carolina Coast. This relatively sharp peak in the spatial distribution of lightning flashes to earth over the Gulf Stream occurs with a width at half‐maximum of approximately 130 km. In the February 1986 data, a close correlation is observed of the maximum lightning flash density contours with the maximum sea surface temperature contours.
Form and behavior of radium, uranium, and thorium in central Pennsylvania soils derived from dolomite
Authors: Greeman Daniel J. , Rose Arthur W. , Jester William A.
Published: February 2008

In a pair of well‐ and poorly‐drained soils developed on Ordovician carbonate rocks in Central Pennsylvania, the distribution with depth and chemical form of 238U, 232Th, and 226Ra have been compared to soil properties. Concentrations range from 3.3 to 8 ppm U and 6.3 to 11 ppm Th in the soils. Although radium is in equilibrium with U at depth in both soils, in surficial A‐horizons Ra is well in excess of U (165–180%). Ra and U are enriched 10X‐12X over the bedrock. Th is enriched, along with Al and Fe, by 20X.

Progressive selective extractions for U, Th, and Ra in soil show half the radium occurring in pedogenic phases, chiefly in the organic fractions (24% of total Ra). By contrast, <1% of the U and Th occurs in any of the organic fractions; up to 80% occurs in the silt and clay fractions with a significant occurrence in the Fe‐oxides, up to 50% for Th.

Ra and chemically similar Ba are cycled by vegetation but Ra is retained in soil, bound in humified soil organic matter while Ba is not. Radon emanation of these soils (8–27%) can be almost entirely attributed to highly emanative Ra bound in organic matter. In these soils the action of vegetation leads to high soil gas radon by maintaining high Ra concentration and enhancing its emanating power.
Radial mode observations from the 5/23/89 MacQuarie Ridge Earthquake
Authors: Park Jeffrey
Published: February 2008

The radial modes 1S0–5S0 axe clearly observable on several long‐period seismic records from the 5/23/89 Macquarie Ridge earthquake. Observations of 0S0 are weaker, but stacking demonstrates significant excitation. Calculations suggest that, for spherical‐earth models, no simple double couple in the uppermost mantle can explain the excitation amplitudes of 1S0–5S0 relative to 0S0. Calculations suggest that the anomalous amplitudes of 1S0–5S0 can be explained by coupling to other modes induced by plausible levels of deep‐earth lateral structure. The coupling of 0S0 is much weaker, and its observed amplitude suggests that roughly 4% of the total moment release inferred from surface wave studies deviated from pure strike‐slip geometry. This can be modeled by ⪎8° deviations from λ = 0°, δ = 90° in a simple double‐couple point source, or by thrust subevents within the main shock.
Geodetic measurement of deformation in the Loma Prieta, California Earthquake with very long baseline interferometry
Authors: Clark T. A. , Ma C. , Sauber J. M. , Ryan J. W. , Gordon D. , Shaffer D. B. , Caprette D. S. , Vandenberg N. R.
Published: February 2008

Following the Loma Prieta earthquake, two mobile Very Long Baseline Interferometry (VLBI) systems operated by the NASA Crustal Dynamics Project and the NOAA National Geodetic Survey were deployed at three previously established VLBI sites in the earthquake area: Fort Ord (near Monterey), the Presidio (in San Francisco) and Point Reyes. From repeated VLBI occupations of these sites since 1983, the pre‐earthquake rates of deformation have been determined with respect to a North American reference frame with 1σ formal standard errors of ∼1 mm/yr. The VLBI measurements immediately following the earthquake showed that the Fort Ord site was displaced 49 ± 4 mm at an azimuth of 11 ± 4° and that the Presidio site was displaced 12 ± 5 mm at an azimuth of 148 ± 13°. No anomalous change was detected at Point Reyes with 1σ uncertainty of 4 mm. The estimated displacements at Ford Ord and the Presidio are consistent with the static displacements predicted on the basis of a coseismic slip model in which slip on the southern segment is shallower than slip on the more northern segment of the fault rupture. We also give the Cartesian positions at epoch 1990.0 of a set of VLBI fiducial stations and the three mobile sites in the vicinity of the earthquake.
Two dimensional hybrid simulation of a curved bow shock
Authors: Thomas V. A. , Winske D.
Published: February 2008

Results are presented from two dimensional hybrid simulations of curved collisionless supercritical shocks, retaining both quasi‐perpendicular and quasi‐parallel sections of the shock in order to study the character and origin of the foreshock ion population. The simulations demonstrate that the foreshock ion population is dominated by ions impinging upon the quasi‐parallel side of the shock, while nonlocal transport from the quasi‐perpendicular side of the shock into the foreshock region is minimal. Further, it is shown that the ions gain energy by drifting significantly in the direction of the convection electric field through multiple shock encounters.
Venus orogenic belt environments: Architecture and origin
Authors: Head James W. , Bruegge Richard W. Vorder , Crumpler L. S.
Published: February 2008

Orogenic belt environments (Danu, Akna, Freyja, and Maxwell Montes) in Western Ishtar Terra, Venus, display a range of architectural elements, including (from the center of Western Ishtar outward) an inboard plateau (Lakshmi Planum), the linear orogenic belts themselves, outboard plateaus, steep scarps bounding Ishtar, adjacent linear foredeeps and outboard rises, and outboard low‐lying volcanic plains. The main elements of the architecture are interpreted to be due to the convergence, underthrusting, and possible subduction of lowland plains at the margins of a preexisting tessera plateau of thicker crust.
Western Ishtar Terra and Lakshmi Planum, Venus: Models of formation and evolotion
Authors: Roberts Kari M. , Head James W.
Published: February 2008

Regional geologic mapping and gravity data reveal a variety of characteristics that must be accounted for in models for the formation and evolution of Western Ishtar Terra and Lakshmi Planum, including: 1) high elevation, 2) plateau‐shaped profile, 3) abnormally steep bounding slopes, 4) foredeeps, 5) polygonal outline, 6) adjacent orogenic belts, 7) volcanic plains, 8) plains emplaced synchronously with orogenic belts, 9) paterae, 10) variable topography of Lakshmi, 11) tessera‐like material underlying Lakshmi, and 12) a large apparent depth of compensation. A tessera/peripheral deformation model, in which a preexisting block of tessera is the locus of convergence of adjacent thinner crust and lithosphere, underthrusting, mountain building, subsurface melting, and plateau uplift, is interpreted to account for most of the characteristics. The apparent depth of compensation is not simply explained by this model and appears to require a second, deeper mantle anomaly component, such as broad mantle upwelling or a hot spot.
Geologic evidence of hotspot activity on Venus: Predictions for Magellan
Authors: Stofan Ellen R. , Saunders R. Stephen
Published: February 2008

A number of distinctive types of geologic features have been identified on Venus that are interpreted to be related to thermal plumes including domal rises, coronae and major composite shield volcanoes. We document the basic characteristics of these features as well as their distribution. The three types of features have related morphologies, and we interpret them to represent a continuum of features formed by mantle plumes at scales from 100's to over 1000 km. The Artemis structure, located in Aphrodite Terra, is proposed to be a large corona. If crustal spreading processes are operating on Venus, hotspot features should form chains on the surface as seen in terrestrial ocean basins. On the basis of current data on hotspot‐related feature distribution on Venus, no clear evidence exists for hotspot chains. The complete distribution of hotspot features in Magellan data will be used to understand better the relationship between interior processes and surface features, as well as to provide a test for the crustal spreading hypothesis.
Lithospheric flexure beneath the Freyja Montes Foredeep, Venus: Constraints on lithospheric thermal gradient and heat flow
Authors: Solomon Sean C. , Head James W.
Published: February 2008

Analysis of Venera 15 and 16 radar images and topographic data from the Freyja Montes region on Venus suggest that this mountain belt formed as a result of a sequence of underthrusts of the lithosphere of the North Polar Plains beneath the highlands of Ishtar Terra, The Freyja Montes deformation zone consists, south to north, of a linear orogenic belt, an adjacent plateau, a steep scarp separating the plateau from the North Polar Plains, a linear depression at the base of the scarp, and an outer rise. The topographic profile of the depression and outer rise are remarkably similar to that of a foreland deep and rise formed by the flexure of the underthrusting plate beneath a terrestrial mountain range. We test the lithospheric flexure hypothesis and we estimate the effective thickness Te of the elastic lithosphere of the underthrusting portion of the North Polar Plains by fitting individual topographic profiles to deflection curves for a broken elastic plate. The theoretical curves fit the observed topographic profiles to within measurement error for values of flexural rigidity D in the range (0.8–3) × 1022 N m, equivalent to Te in the range 11–18 km. Under the assumption that the base of the mechanical lithosphere is limited by the creep strength of olivine, the mean lithospheric thermal gradient is 14–23 K/km. The portion of the North Polar Plains to the immediate north of Freyja Montes stands at a regional elevation very near the modal elevation for the planet, so the inferred elastic lithosphere thickness and thermal gradient may be at least approximately representative of a significant fraction of the Venus lithosphere. That the inferred thermal gradient is similar to the value expected for the global mean gradient on the basis of scaling from Earth provides support for the hypothesis that simple conduction dominates lithospheric heat transport on Venus relative to lithospheric recycling and volcanism.
Energy constraints on kinematic models of oblique faulting: Loma Prieta versus Parkfield‐Coalinga
Authors: Michael Andrew J.
Published: February 2008

The Loma Prieta earthquake was a combination of right lateral strike‐slip and reverse faulting. This oblique motion has been explained by a kinematic model that has the fault accommodate both the translation and convergence required by the Pacific‐North American plate motions and a local bend in the San Andreas Fault However, in other areas of California, such as Parkfield‐Coalinga, this combination of motions is taken up by decoupled strike‐slip and thrust faults. In this paper I develop a simple physical model, based on applying Hamilton's principle to the energy released in earthquakes, that allows us to determine if a region should undergo oblique or decoupled faulting. This determination depends on the dip of available faults and the amount of convergence relative to the amount of translation. These energy constraints correctly predict the different types of faulting at Loma Prieta and Parkfield‐Coalinga.
Rotation Of the Colorado Plateau: An updated analysis of paleomagnetic poles
Authors: Bryan Phillip , Gordon Richard G.
Published: February 2008

All available Jurassic, Triassic, and late Paleozoic paleomagnetic poles from the Colorado Plateau and stable North America are used to estimate the rotation of the Colorado Plateau relative to stable North America since Jurassic time. The paleomagnetic poles differ from those of our prior study [Bryan and Gordon, 1986] through the addition of seven recently published poles, the deletion of one pole, and the replacement of two others. We also improve on our prior analysis by omitting Cretaceous poles. From the systematic offset between plateau poles and stable North American poles we estimate rotation of the Colorado Plateau to be
(95% confidence limits) clockwise, ∼1° larger than we found before. The null hypothesis of no systematic difference between plateau poles and stable North American poles can be rejected with a formally high level of confidence (99.99%). The hypothesis that the systematic differences between plateau and off‐plateau poles is as large as 10°, as proposed by several workers using fewer poles, can be rejected at an equally high level of confidence.
Slow crack growth and aftershock sequences
Authors: Reuschlé Thierry
Published: February 2008

We conducted a critical reexamination of Yamashita & Knopoff's (1987) models of aftershock occurrence, based on slow crack growth process. Such models assume that a time‐dependent process like slow crack growth, extensively documented at the sample scale, can be straightforwardly extrapolated to the field scale. If it is so, a question is rised : which model is the most consistent one with real data? We suggest here a possible way of discriminating between these models. The first model considers the slow growth of a main fracture surrounding small, locked asperities until slippage occurs. The second model considers the slow growth of satellite faults around the main fracture up to coalescence. By assuming power law distributions for the critical distances for quasistatic and dynamic crack growth, numerical simulations show that both models correctly predict Omori's law as well as the classical magnitude‐frequency law. Nevertheless, when looking further at the time distribution of aftershock magnitudes, it is shown that the results derived from the second model are inconsistent with usual observations since inverse sequence is predicted. Results derived from the first model are more realistic.
Seasonal and inter‐annual variations in Antarctic sea ice extent as mapped by radar altimetry
Authors: Laxon Seymour
Published: February 2008

Previous work has shown that interannual variations in total sea ice extent may provide a sensitive indicator of global climate change. Data from passive microwave instruments have allowed mapping of global sea ice extents from 1973–76 and from 1978 up to September 1987, [Gloerson and Campbell, 1988]. In this paper data from another microwave instrument, the Geosat radar altimeter, have been used to map the Antarctic sea ice extent for the period November 1986 to January 1989. Comparison with total Antarctic sea ice extents derived from the Scanning Multichannel Microwave Radiometer (SMMR) show excellent agreement during the freeze up period but show significant differences during the late part of the melt period.
The scattering rate of solar 834 Å radiation by magnetospheric O+ and O++
Authors: Meier R. R.
Published: February 2008

Several recent proposals to image sunlit magnetospheric O+ have been difficult to assess because of the lack of detailed knowledge of the solar spectrum at 834 Å. An NRL solar spectrograph flown on a sounding rocket in 1962 actually had sufficient resolving power to allow the calculation of scattering rates. Using these solar data, examples of scattering rates for a range of thermal and bulk velocities are presented for both O+ and O++, and the effects of ionospheric albedo are estimated. The scattering rates are significantly lower than previously estimated for hot or moving plasma and exhibit substantial structure.
Electrostatic electron and ion cyclotron harmonic waves in Neptune's magnetosphere
Authors: Barbosa D. D. , Kurth W. S. , Cairns I. H. , Gurnett D. A. , Poynter R. L.
Published: February 2008

Voyager 2 observations of electrostatic electron and ion cyclotron waves detected in Neptune's magnetosphere are presented. Both types of emission appear in a frequency band above the electron and ion (proton) cyclotron frequencies, respectively, and are tightly confined to the magnetic equator occurring within a few degrees of it. The electron cyclotron waves are interpreted as electron Bernstein modes including an intense upper hybrid resonance emission excited by an unstable loss cone distribution of low‐density superthermal electrons. The ion cyclotron waves are interpreted as hydrogen Bernstein modes including an intense lower hybrid resonance emission excited by an unstable ring distribution of low‐density pickup N+ ions deriving from the satellite Triton.
Convection in Neptune's magnetosphere
Authors: Hill T. W. , Dessler A. J.
Published: February 2008

We assume that nonthermal escape from Triton's atmosphere produces a co‐orbiting torus of un‐ionized gas (presumably nitrogen and hydrogen) that subsequently becomes ionized by electron impact to populate a partial Triton torus analogous to the Io plasma torus in Jupiter's magnetosphere. Centrifugal and magnetic‐mirror forces confine the ions to a plasma sheet located between the magnetic and centrifugal equators. The ionization rate, and the torus ion concentration, is strongly peaked at the two points (approximately 180° apart in longitude) at which Triton's orbit intersects the plasma equator. During the course of Neptune's rotation these intersection points trace out two arcs roughly 75° in longitudinal extent, which we take to be the configuration of the resulting (partial) plasma torus. The partial ring currents produce a quadrupolar (four‐cell) convection system that provides rapid outward transport of from the arcs. Ring‐current shielding, however, prevents this convection system from penetrating very far inside the plasma‐arc distance. We suggest that this convection/shielding process accounts for the radial confinement of ≳150 keV trapped particles within L ≈ 14.3 as observed by the Voyager LECP instrument.
Global magnetic anomaly and aurora of Neptune
Authors: Cheng Andrew F.
Published: February 2008

The large offset and tilt of Neptune's dipole magnetic field combine to create a global magnetic anomaly, analogous to but much more important than Earth's South Atlantic Anomaly. Energetic particle precipitation loss within the Neptune anomaly creates “Atmospheric drift shadows” within which particle fluxes are greatly reduced. The energetic particle dropout observed by Voyager near closest approach occurred near the predicted times when Voyager passed within the atmospheric drift shadow. Extremely soft, structured bursts of ions and electrons within the drift shadow may result from plasma wave‐induced pitch angle scattering of trapped particles confined near the magnetic equator. The dropout does not necessarily imply that Voyager passed through an Earth‐like discrete auroral zone, as earlier reported. The ion and electron fluxes observed within the dropout period correspond to particles that must precipitate to Neptune's atmosphere within the anomaly region. This anomaly precipitation can account for a major portion of the ultraviolet emissions previously identified as Neptune aurora.
The photochemistry of methane in the atmosphere of Triton
Authors: Strobel Darrell F. , Simmers Michael E. , Herbert Floyd , Sandel Bill R.
Published: February 2008

The photochemistry of methane in Triton's atmosphere is driven by approximately equal contributions of solar and local Interstellar medium (LISM) Lyα and in combination with weak vertical mixing, K ∼ 4 × 103 in the winter hemisphere and 8 × 103 cm2 s−1 in the summer hemisphere, yields the observed CH4 scale heights of ∼ 9 km below 70 km altitude (Broadfoot et al., 1989). The hemispheric difference in K is consistent with a seasonal meridional circulation with upwelling in the summer hemisphere and downwelling in the winter hemisphere. Methane photolysis produces H2 molecules which are removed from the photolysis region by an upward flux ( ∼ 1.5 × 108 cm−2 s−1, normalized to the surface) to the ionosphere where ion reactions convert H2 to H. This results in a hydrogen escape flux of 3 × 108 cm−2 s−1. The H column density is ∼ (5−10) × 1014 cm−2 and resonantly scatters ∼ 26 R of solar Lya consistent with the day‐night asymmetry observed by the Voyager UVS. The inferred surface mixing ratios of CH4 indicate subsaturated conditions. The CH4 photolysis rate is sufficient to generate a smog of condensed C2H2, C2H4, C2H5, and C4H2 particles in the lowest 30 km of Triton's atmosphere with an optical depth consistent with Voyager imaging results.
Post Voyager comparisons of the interiors of Uranus and Neptune
Authors: Podolak M. , Reynolds R. T. , Young R.
Published: February 2008

The recent Voyager flyby of Uranus and Neptune has provided refined values for the gravitational moments and rotation periods of those planets. Using these new parameters, models of the interiors of these planets show that their density distributions are very similar. This lends support to the conjecture that their compositions are similar as well. The models are indeed consistent with such a conjecture. The difference in the internal heat sources of these two planets may be due to the fact that heat transport from the interior of Uranus is inhibited by a statically stable interior.
Observations of Neptunian rings by Voyager Photopolarmeter Experiment
Authors: Horn Linda J. , Hui John , Lane Arthur L. , Colwell Joshua E.
Published: February 2008

The Voyager photopolarimeter experiment detected the Neptunian rings 1989N1R and possibly 1989N2R. These rings were also photographed by the Voyager imaging cameras in August 1989. Our firm detection of 1989N1R has an equivalent depth (the product of the radial width and mean normal optical depth) of 0.77 +/− 0.13 km, while a less certain detection of 1989N2R has an equivalent depth of 0.7 km +/− 0.2 km. Several statistical techniques were used to for additional material in the Neptune ring system and none was identified at a high confidence level.
KOYAANISMUUYAW: THE HYPOTHESIS OF A PERENNIALLY DICHOTOMOUS TRITON
Authors: Moore Jeffrey M. , Spencer John R.
Published: February 2008

The Voyager 2 observation that, at the height of a “major” southern summer, the southern “cap” of Triton extends nearly to the equator, and the northern temperate regions (where they can be seen) are relatively dark even though nitrogen frost should be accumulating at those latitudes, has prompted us to propose a hypothesis that there has been a net non‐reversable flux of surficial volatiles on Triton from the northern hemisphere to the southern hemisphere over much of the satellite's history and up to the present. The north‐south hemispherical albedo difference is permanent and overwhelms the seasonal effect on volatile transport. This hypothesis assumes that volatile erosion, transport, and deposition has been in the form of sublimation, advection, and precipitation.
NITROGEN FROST MIGRATION ON TRITON: A historical model
Authors: Spencer John R.
Published: February 2008

I present the results of numerical simulation of the seasonal migration of nitrogen frost on Triton constrained by Voyager observations of atmospheric pressure, temperature, and albedo distribution. Most of the exposed nitrogen is probably seasonal frost, whose migration can produce major variations in atmospheric pressure. For instance, models explored here predict a tenfold pressure drop in the coming decade. The observed patterns can be understood if fresh nitrogen frost is relatively dark but brightens with increasing insolation in a manner analogous to the Martian southern CO2 cap.
The local magnitude of the 18 October 1989 Santa Cruz Mountains Earthquake is ML=6.9
Authors: McNally K. C. , Yellin J. , Protti‐Quesada M. , Simila G. , Malavassi E. , Shillinger W. , Terdiman R. , Zhang Z.
Published: February 2008

We find that the local magnitude, ML, of the 18 October 1989 (U.T.) earthquake is 6.9, not 7.0 ‐ 7.1 as has tea reported. This value agrees with the moment magnitude, Mw = 6.9, found by Kanamori and Satake (1990).
Discrete phase changes within nonlinear steepened magnetosonic waves: Comet Giacobini‐Zinner
Authors: Tsurutani Bruce T. , Smith Edward J. , Buti B. , Matsumto Hiroshi , Brinca Armando
Published: February 2008

In this letter, we will illustrate the intricate complexities of nonlinear wave evolution and briefly discuss their consequences. We will show examples of nonlinear steepened magnetosonic waves that have subintervals without phase rotation (linearly polarized) and other subintervals with discrete, rapid phase rotation. Some specific features are: 1) the trailing (∼half) portion of the wave sometimes has no phase rotation and is simply compressive; 2) just behind the leading adge of the wave front where there is a sharp rotation (called a partial rotation), there is often a second region with no phase change; 3) between these two regions is an interval with a distinct phase change; 4) in the examples shown in this paper, the distinct phase changes have right‐hand polarizations in the spacecraft frame; 5) the magnetosonic wave appears to split into two parts with time; the right‐hand rotation is located where the splitting occurs.

Possible explanations for the right‐hand rotation will be explored. One plausible explanation is that a right‐hand wave is generated through the decay instability of a magnetosonic wave, i.e., a magnetosonic wave propagating towards the sun decays into a sound wave and a magnetosonic wave propagating away from the sun. If right‐hand daughter waves are actually present, this will have important consequences. Even though these waves are present only ∼ 10% (or less) of the time, this may allow significant wave‐particle interactions to make the self‐consistent second‐order Fermi acceleration mechanism of energetic cometary ions feasible.
On the existence of purely transverse field‐line oscillations
Authors: Rajaram R. , Venkatesan D.
Published: February 2008

We have shown that transverse toroidal (or poloidal) oscillations are possible in a dipole field, provided they are sufficiently localized in radial (azimuthal) direction for the Hall current‐generated electric fields to be relevant. Explicit solutions are obtained for azimuthal oscillations and it is shown that these are localized in the radial direction with an exponential decay length
in the equatorial plane; where L0 is the equatorial distance of the field line; ω and ωci are field line resonance and ion cyclotron frequencies, and k is the zonal wave number of the mode. It is also shown that a superposition of a continuum of such structures centered over a range of L values can generate the fluctuations that are observed.
Topography of the ocean floor: Thermal evolution of the lithosphere and interaction of deep mantle heterogeneities with the lithosphere
Authors: Colin Paul , Fleitout Luce
Published: February 2008

Topography associated with large wave‐length geoid is derived by two methods. First, the bathymetry corrected for sediment loading is decomposed using a least‐squares method as a function of age plus terms proportional to the geoid. The topography at old ages is flatter predicted by the
law. At degrees 2 and 3, very little topography is associated with the geoid. The transfer function is not even certain in sign but is never smaller than 0.6. More topography seems associated with higher degree harmonics (6 and 7). Second, the function of age alone best fitting the topography is determined. The correlation coefficients of the residual topography with the geoid are then computed. A slight correlation appears for degree 6, but not for degrees 2 and 3. These results suggest a, mechanical decoupling between the lower mantle mass heterogeneities and the lithosphere.
Electron acceleration by magnetosonic waves in solar flares
Authors: Zweibel Ellen G. , de La Beaujardière Jean‐François
Published: February 2008

Results of a simulation of electron acceleration by magnetosonic waves in a solar coronal loop are presented. The dependence of the energization rate on the strength and shape of the wave spectrum is discussed. Comparisons are made with the predictions of quasilinear theory and of a model describing stochastic acceleration by waves as isotropic diffusion in momentum space.
Evaluation of the paleo‐geothermal gradient at Site 768 (Sulu Sea)
Authors: Berner Ulrich , Bertrand Philippe
Published: February 2008

Paleo‐temperature gradients for Site 768 are determined by modelling organic maturities. It is found that the measured maturity of the organic matter cannot be attributed to the present‐day thermal gradient of 130°C/KM. From a comparison between modelled and measured maturities a high paleogradient of 250°C/KM is derived.
Comparison of time‐ and frequency‐domain techniques for wind velocity estimation using multiple‐receiver MF radar data
Authors: Franke Patricia M. , Thorsen Denise , Champion Mark , Franke Steven J. , Kudeki Erhan
Published: February 2008

Multiple‐receiver MF radar returns from the mesosphere are used to investigate the relationship between spaced antenna (SA), radar interferometry (RI), and imaging Doppler interferometry (IDI) wind estimation techniques. Our results show that frequency‐domain (RI and IDI) and time‐domain (SA) techniques yield almost identical results under high SNR conditions suitable for SA full correlation analysis (FCA).
Plasma sheet convection and the stability of the magnetotail
Authors: Pritchett P. L. , Coroniti F. V.
Published: February 2008

Particle simulations are used to investigate the effects of plasma sheet convection into regions of increasing tail lobe magnetic field strength on the stability of a magnetotail equilibrium. The self‐consistent treatment of convection first drives Bz to zero on axis in the region of the strongest lobe field Bz and then causes the equilibrium to break due to the rapid growth of tearing modes driven by the induced temperature anisotropy. The net result is the evolution of the inward‐convecting plasma sheet into a slowly moving or stagnant plasmoid. The time scale for this process is much more rapid than that associated with particle drift losses across the tail. These results support the suggestion that steady convection within the plasma sheet may not be possible.
Cold ion beams in the low latitude boundary layer during accelerated flow events
Authors: Gosling J. T. , Thomsen M. F. , Bame S. J. , Elphic R. C. , Russell C. T.
Published: February 2008

Measurements made with the Fast Plasma Experiment on ISEE 1 and 2 reveal that accelerated beams of cold (1–30 eV for H+) ions are present sporadically on reconnected field lines within the low latitude boundary layer, LLBL. H+ normally is the major constituent of these beams, but He+ and O+ are also occasionally detected in variable concentrations. Because of the low temperatures and the compositional makeup of these beams, the ionosphere must ultimately be the source of these ions. Observed beam speeds (between 120 and 250 km s−1) are always less than that of the magnetosheath ions which penetrate into the LLBL on reconnected field lines, but both ion populations share the same E×B convective drift. Analysis reveals that reflection at the magnetopause cannot be the mechanism accelerating these ions. A more likely possibility is that the ions are accelerated primarily by the large transverse drift of recently reconnected field lines.
Jupiter's north and south polar aurorae with IUE data
Authors: Livengood T. A. , Moos H. W.
Published: February 2008

Observations of Jupiter's auroral H2 emissions with the IUE spacecraft, from 1978 through 1990, show that aurorae at the two poles are similar in several respects: (a) emission intensity is modulated with magnetic longitude, north peak emission at λIII(1965) ∼ 200°; south peak at λIII(1965) ∼ 20°; (b) emission intensity and degree of modulation are comparable for both poles; (c) attenuation by hydrocarbons varies in phase with the intensity, peak attenuation coinciding approximately with peak emission. Increases in the hydrocarbon column are an indicator of either enhanced penetration depth and thus energy of the auroral primaries, or of increases in the high‐altitude hydrocarbon content caused by modification of the local atmosphere.
The physical nature of ball lightning
Authors: Muldrew D. B.
Published: February 2008

Ball lightning (BL) is mathematically modelled assuming a solid, positively charged core exists at its center. The large amount of energy occasionally associated with BL is mainly due to the electrostatic (ES) energy of the charge on the core. The upper energy limit is determined by the size and strength of the core and this energy can be orders of magnitude greater than the energy which can be confined by atmospheric pressure alone. A pure electron layer and a plasma layer surround the core. The charge of the electron layer is equal in magnitude to that of the core. An electromagnetic (EM) field is completely trapped by the electron and plasma layers. The electron temperature is sufficiently high that absorption by electron‐ion collisions is small, enabling the ball to have a lifetime of seconds or more. The ponderomotive force (radiation pressure) of the trapped EM field balances the ES force of the electrons toward the core plus the force of atmospheric pressure. The generation mechanism is not considered.
Evidence for a diurnally rocking plasma mantle at Neptune
Authors: Zhang Ming , Vasyliunas V. M. , Siscoe G. L. , Lepping R. P. , Ness N. F.
Published: February 2008

Voyager's post‐encounter trajectory at Neptune allows the directions of the magnetic field in the magnetosheath produced by the draping of the typical interplanetary field and by alignment with the magnetotail to be distinguished. Changes of the field from the draped to the magnetotail‐aligned direction accompanied by decreases of plasma velocity, density, and temperature, observed at intervals of approximately a Neptunian day, are consistent with the assumption that Voyager repeatedly encountered a plasma mantle region extending well into the magnetosheath and modulated by the rotation of the planet's magnetic dipole. Other interpretations are either implausible or inconsistent with the observations. Previously reported periodic velocity decreases in the magnetosheath of Uranus can be interpreted in the same way. Extended plasma mantles may thus be a general property of planetary magnetospheres interacting with the magnetized solar wind. Analogous effects at Earth cannot yet be observed because of lack of suitable spacecraft missions, but their existence is suggested by theoretical arguments.
Iron atom densities in the polar mesosphere from lidar observations
Authors: Alpers Matthias , Höffner Josef , von Zahn Ulf
Published: February 2008

Between March 24 and April 6, 1990, we performed lidar measurements of iron densities above Andøtya, Norway (69° N). In each of the five nights of measurements we observed a regular Fe layer which was confined to the altitude region between 80 and 100 km. Its peak Fe densities occurred at (84.5 ±1) km or approximately 6 km lower than the peak of the sodium layer as observed by us two weeks earlier. The regular Fe layer exhibited column densities of (9 ± 4) ·109 cm−2 and maximum number densities close to 7,000 cm−3. In addition, sporadic Fe layers were observed frequently between 88 and 108 km, one of which reached a maximum number density of 78,000 cm−3 near 97 km altitude. Properties of the Fe layers as observed by us are compared to those observed by Granier et al. [1989] and by Bills and Gardner [1990].
The influence of ocean tide model corrections on geosat mesoscale variability maps of the north east Atlantic
Authors: Tomas J. P. , Woodworth Philip L.
Published: February 2008

A two year GEOSAT radar altimeter dataset has been analysed by repeat profile methods to produce mesoscale variability maps of the North East Atlantic. Significant differences have been found between maps produced using two different ocean tide models for corrections to the sea surface height measurements. The area of the Iceland‐Faeroes Front is particularly affected. Large values of sea surface height variability found here when the Schwiderski ocean tide model is used, are considerably reduced when a model developed by Flather is used. The latter model is known to be more accurate overall for the north east Atlantic region. The fact that model errors can produce mesoscale variability values larger than those expected from the frontal processes emphasises once again the need for a general improvement in tidal knowledge.
An estimate of the amount of material removed from the Martian fretted terrain
Authors: Dimitriou Andrew
Published: February 2008

Three models are proposed for the former extent of a continuous heavily cratered plateau within the present area of fretted terrain between 270°W and 360°W. To the south and west, each model area limit is well constrained by the northern boundary of the unfretted heavily cratered plateau. The northern limit of each model is defined by the gradational northern limit of fretted terrain. The eastern limits are distinct for each model. Model 1 assumes a once continuous plateau was dropped to the north along NW‐trending normal boundary faults in the Ismenius Lacus SE subquadrangle. Model 2 includes model area 1 and places the former limit of the plateau 400 km farther east along a trace subparallel to the present plateau margin in this subquadrangle. Model 3 includes model area 2 and uses the rim of the proposed Borealis basin in Casius SW subquadrangle [Wilhelms and Squyres, 1984] as the eastern limit of the former plateau.

The estimates for the amount of material removed vary from 1.04 ± 0.60 × 106 km3 for model 1 through 1.53 ± 0.80 × 106 km3 for model 2 to 1.99 ± 1.01 × 106 km3 for model 3. This implies that this area of fretted terrain is not a significant source of sediment for the northern lowlands of Mars.
Photoelectron flux buildup in the plasmasphere
Authors: Mantas George P. , Carlson Herbert C. , Wickwar Vincent B.
Published: February 2008

Processes which confine photoelectrons to the plasmasphere (e.g., collisional backscattering from the thermosphere and magnetic trapping due to pitch angle redistribution through Coulomb collisions in the plasmasphere) tend to increase the steady state photoelectron flux in the plasmasphere above the amplitude level that would otherwise have been attained. Theoretical calculations are presented of steady state photoelectron fluxes in the plasmasphere, for specified atmospheric and ionospheric conditions. (Observational plasma line intensity data for these conditions exist and will be compared elsewhere.) General features of the angular distribution are presented and compared with observations. The transparency of the plasmasphere and the backscattering properties of the thermosphere are investigated. The buildup effect due to collisional backscatter alone is calculated, and the combined buildup effect of pitch angle diffusion and backscatter is estimated. It is found that the inclusion of these effects increases the steady state photoelectron flux amplitude in the plasmasphere by about 50% over the value obtained when the buildup effects are neglected. The calculated steady state photoelectron fluxes in the plasmasphere are in good agreement with the available observations.
On the polarization and origin of auroral kilometric radiation
Authors: Gurnett Donald A. , Green James Lauer
Published: February 2008

Observations of radio emissions by the Hawkeye 1 satellite at low altitudes over the southern hemisphere have now provided measurements at radial distances from about 1.5 to 2.5 RE along the auroral field lines, in the region where the intense nightside auroral kilometric radiation is believed to be generated. These measurements provide new evidence on the mode of propagation and origin of the auroral kilometric radiation. At low altitudes the auroral kilometric radiation is consistently observed to have a low‐frequency cutoff at the local electron gyrofrequency fg−. Since the electron plasma frequency fp− is usually much smaller than fg− in the region where these observations are obtained, this cutoff corresponds closely with the propagation cutoff for the right‐hand mode of propagation. These observations therefore provide a strong indication that the auroral kilometric radiation is right‐hand polarized in agreement with previous conclusions made on the basis of the angular distribution of this radiation. In the local evening region, where the intense auroral kilometric radiation is believed to be generated, a few events have been detected for which no low‐frequency cutoff is evident. In these cases the auroral kilometric radiation appears to merge essentially continuously into a band of intense auroral hiss which extends downward to frequencies as low as 1 kHz. These observations suggest that the generation of the whistler mode auroral hiss and the escaping auroral kilometric radiation are very closely related. Possible mechanisms which could produce strong coupling between the whistler mode and the escaping free space electromagnetic modes are discussed.