bluuebunny/crossref_metadata_2025 huggingface dataset:
Upstream energetic ions under radial IMF: A critical test of the Fermi Model
Authors: Sarris E. T. , Krimigis S. M.
Published: February 2008

We have surveyed eight years of interplanetary magnetic field (IMF) and energetic particle observations obtained by the IMP‐8 spacecraft upstream from the bow shock and accumulated 63 cases when the upstream IMF remained radial for extended periods of time (> 1 hour). Of these, two cases have been selected during which measurable fluxes of ambient solar or corotating energetic particle events were absent. These conditions provide an excellent test to the theories of the origin of upstream energetic ions. It is shown that there are extended periods with radial IMF when no upstream energetic ions (E ≥ 50 keV) were detected. It is further shown that energetic ions in the range 50 keV ≤ E ≤ 1 MeV are not continuously present but appear in bursts of intensities varying by more than an order of magnitude under persistently radial IMF. These measurements contradict a fundamental prediction of the Fermi mechanism for the origin of the upstream energetic ions, namely that such ions should always be present on radial IMF lines. The observations are consistent with the hypothesis that energetic (≳ 50 keV) ions leak out from, and appear in the upstream medium sporadically, following the onset of magnetic activity within the magnetosphere.
On the temporal change of stratospheric NO2
Authors: Coffey M. T.
Published: February 2008

Ground based, aircraft and satellite measurements of stratospheric NO2 are examined to establish the long term temporal trend in the column amount. Observations at 40° and 70° latitude in both hemispheres show a consistent annual cycle but no long term trend is observed in the period from 1975 to 1986.
10th of April 1987 seismic swarm: Correlation with geochemical parameters in Campi Flegrei Caldera (southern Italy)
Authors: Tedesco Dario , Bottiglieri Luisa , Pece Raimondo
Published: February 2008

A close relationship between geophysical activity (seismicity and ground deformation) and chemical changes in volcanic reservoirs has been proposed several times in active volcanic areas. In Campi Flegrei caldera, especially during the bradyseismic crisis which occurred between 1982‐1984, this correlation was never clearly demonstrated because of the high rate of occurrence of earthquakes and the small number of gas samples.

After at least two years of both geochemically and geophysically quiescent period, a swarm of 50 earthquakes, felt in the area of the Solfatara crater with 2.0 maximum magnitude, occurred on the 10th of April 1987. At about the same time (before and after), several geochemical parameters showed important changes in concentration. These include water vapour, nitrogen, hydrogen, methane and to a lesser extent hydrogen sulfide in fumarolic gases from Bocca Grande fumarole in the Solfatara crater and the radon content in water wells situated far from the swarm epicentral area. In our opinion, the processes causing the geochemical changes are linked to aseismic creeping mechanisms, which leads to an easier rising of fluids in fumaroles (H2O, N2, H2 and CH4) and in the superficial water table (Rn).

The subsequent seismicity could be related to consequent local stress accumulation on gas reservoir rocks induced by creeping.
Strong core magnetic fields in magnetopause flux transfer events
Authors: Scholer Manfred
Published: February 2008

Magnetic field measurements in flux transfer events (FTEs) at the Earth's magnetopause often reveal the existence of a strong core magnetic field. We describe a possible mechanism for the origin of such strong core fields in the framework of a recently proposed model for FTEs. In this model bursty reconnection at a single X line, which extends over a large longitude segment, leads to loop like magnetic fields. As these loops move due to the Maxwell stress along the magnetopause, the magnetopause magnetic field directed perpendicular to the loops is swept up and correspondingly enhanced. When the downward pulling force due to the stress of the swept up magnetopause field equals the upward pulling force due to the loops an electromagnetic force equilibrium is reached. The core field strength determined by the force balance is proportional to the longitude extent of the reconnection line. Events with a large core field are therefore expected to have a higher detection probability than events with a small core field.
A search for iridium in the Deccan Traps and Inter‐Traps
Authors: Rocchia R. , Boclet D. , Courtillot V. , Jaeger J. J.
Published: February 2008

It has been suggested that flood basalts in the Deccan (India) might be associated with events at the Cretaceous‐Tertiary boundary (KTB). A search for iridium in 47 samples from lava flows and inter‐trap sediments in the Deccan yields negative results. Concentrations are not statistically different from zero, with a minimum detection level on the order of 0.1 ng.g−1 (ppb). This does not help to constrain the debate on the internal vs external origin of KTB boundary events, since for instance Ir could have been outgassed from the magma, and original concentrations of only 0.05 ng.g−1 prior to outgassing are sufficient to account for the worldwide Ir excess mass at the KTB.
Antarctic measurements of ozone by SAGE II in the spring of 1985, 1986, and 1987
Authors: McCormick M. P. , Larsen J. C.
Published: February 2008

Vertical profiles of ozone obtained by the Stratospheric Aerosol and Gas Experiment II (SAGE II) inside the southern polar vortex indicate ozone depletion increased dramatically in October 1987 when compared to the previous worst year, 1985. Minimum observed October concentrations dropped from about 4.E+11 to 1.E+11 (molecules/cm³) at 16 km, while minimum total column sums (above 100 mb) dropped by 15%. The top altitude of the depletion region shows a slight correlation with depletion severity in October, being located at 22‐23 km in 1985, 22 km in 1986, and consistently at 23 km in 1987. A less severe downward trend in ozone is observed in September. Vertical profiles of ozone within the vortex are presented for September and October 1987 and compared to 1985 and 1986.
Active faulting near the Cajon Pass well, southern California; Implications for the stress orientation near the San Andreas Fault
Authors: Weldon Ray J. , Springer James E.
Published: February 2008

The DOSECC Cajon Pass well is located 4 km NE of the San Andreas fault in a region that includes a diversity of secondary structures. Active faults close to the well are subparallel to the right‐lateral San Andreas fault but exhibit left‐lateral and normal slip. The stress orientation measured in the well is not consistent with right‐lateral slip on the San Andreas fault or the stresses inferred from focal mechanisms of earthquakes within 10 km of the fault, but may drive the E‐striking, slightly normal, left‐lateral Cleghorn fault, the closest active fault to the well. If the in‐situ stress is everywhere consistent with the highly variable styles of active secondary faulting like the Cleghorn, the orientation of stresses along the San Andreas fault may be quite variable.
Hydraulic fracturing in situ stress measurements to 2.1 km depth at Cajon Pass, California
Authors: Healy John H. , Zoback Mark D.
Published: February 2008

Stress measurements to 2.1 km reveal stress changes with depth that cannot be explained by an elastic response to uniform crustal strain. The data at about 1 km depth suggest that the stress is limited by the frictional strength of rock and is perturbed at greater depths by faults which intersect the borehole. The stress data indicate that there is little or no right‐lateral shear stress acting on planes parallel to the San Andreas fault.
CEDAR lidar observations of sporadic Na layers at Urbana, Illinois
Authors: Beatty Timothy J. , Bills Richard E. , Kwon Kang H. , Gardner Chester S.
Published: February 2008

In March and April of 1988 five short‐lived sporadic Na layers were observed in the late evening above Urbana, IL (40°N, 88°W) with the new CEDAR lidar instrument. The layers were very narrow (∼140 m FWHM) and very dense with maximum densities exceeding 24,000 cm−3. The layers formed in the late evening between 2100 LST and midnight at altitudes between 82 and 89 km. The average duration of the layers was 100 s. Some of the layers moved rapidly, both upward and downward, with velocities as high as 9 ms−1. Compared to similar phenomena observed at Andoya, Norway [von Zahn et al., 1987] and Mauna Kea, Hawaii [Kwon et al., 1988], the sporadic layers above Urbana appear to occur much less frequently at generally lower altitudes, contain less Na and are of much shorter duration. The five sporadic Na layers described in this letter may have resulted from the advection of meteor trails across the lidar field‐of‐view.
Nitric acid aerosols at the tropical tropopause
Authors: Hamill Patrick , Fiocco G.
Published: February 2008

It is thermodynamically possible for nitric acid aerosol particles to form in the lower stratosphere and upper troposphere in tropical latitudes. This aerosol would have essentially the same composition as the polar stratospheric clouds observed in the winter polar stratosphere. We have carried out calculations indicating that nitric acid aerosols may form at the same altitudes as layers observed in the tropics by the SAGE satellite system.
Ozone in seawater and Lake Water: A reversible reservoir
Authors: Harvey George R. , Springer‐Young Margie
Published: February 2008

Observations made at sea and examination of global ozone monitoring data from oceanic sites indicate that ozone mixing ratios over the sea surface often increase with increasing wind speed. However, the slope of the increase approaches zero at wind speeds above about 6 m/sec (13 kts). Subsequent laboratory experiments confirmed that ozone can be purged from any seawater sample whether freshly collected, stored, or from depth. Samples of Lake Michigan water are purged of ozone in less time than seawater and its capacity is less than that of seawater. The rate of evolution of ozone is increased by altering the pH, changing the ionic strength by the addition of salts or by evaporation. These results suggest that a significant portion of tropospheric boundary layer ozone mixing ratios could be maintained by a reversible equilibrium with the ocean and lake surfaces.
Extended sodium exosphere of the Moon
Authors: Potter A. E. , Morgan T. H.
Published: February 2008

Sodium emission has been observed up to 1200 km above the subsolar limb of the Moon at third quarter. The intensity of the emission is far in excess of that predicted from the scale height and surface density derived previously from measurements of sodium emission at low altitudes above the lunar surface. This can be explained by assuming that there are both “hot” and “cold” components of the lunar sodium exosphere. The “hot” sodium atoms which produce the extended component of the exospheric emission are those which have been freshly introduced to the lunar exosphere by meteoric impact or solar wind sputtering, and the “cold” sodium atoms are those which have collisionally accommodated to the lunar surface. From the density and apparent temperature of “hot” component we derive a sodium supply rate of 0.72*105 atoms cm−2 s−1 in agreement with rates calculated for impact vaporization and charged particle sputtering of 0.97*105 atoms cm−2 s−1 and 0.5*105 atoms cm−2 s−1, respectively. Since some fraction of the sodium evolved by both impact vaporization and sputtering will possess escape velocity, there may be a sodium coma.
New estimates of oceanic tidal energy dissipation from satellite altimetry
Authors: Cartwright David E. , Ray Richard D.
Published: February 2008

As a novel approach to computing the flux of tidal power into shelf areas, tidal maps of an oceanic area near the Patagonian Shelf are derived from 11 months of altimetry records from the GEOSAT satellite. Power fluxes are computed from the maps through Laplace's tidal equations. Flux vectors for M2 clearly show a convergence on to the southern portion of the shelf sea and their total is nearly twice the loss computed by Miller for that area. A decrease of ‘quality factor' with frequency from M2 to S2 is in keeping with Webb's hypothesis of shelf resonances at frequencies a little higher than the tidal band.
Charge transfer by point discharge below dust storms
Authors: Kamra A. K.
Published: February 2008

Measurements of point discharge current from an artificial point raised below dust storms at Roorkee (India) show that in this area a negative charge of 1177 C/Km²/year can be transferred to earth by this process alone. Although, this process can operate only in particular regions of earth surface, the net charge transfer to earth in such regions is debateable.
A reassessment of the heat transport by variable viscosity convection with plates and lids
Authors: Gurnis Michael
Published: February 2008

The heat transport by a viscous fluid with temperature dependent viscosity has been studied numerically. As opposed to previous models, the top surface of the fluid clearly defines a tectonic plate with horizontally uniform velocity and subduction. Past studies failed to incorporate plates resulting in inefficient heat transport. With tectonic plates, the heat transport is as efficient as Rayleigh‐Benard convection with constant viscosity; there is a strong buffering between internal temperature and heat loss. Past studies of parameterized convection which incorporated parameters indicative of a strong buffering between internal temperature and total heat output still provide the most physically plausible representation of the Earth's thermal evolution.
Singularity spectrum of intermittent seismic tremor at Kilauea Volcano, Hawaii
Authors: Shaw Herbert R. , Chouet Bernard
Published: February 2008

Fractal singularity analysis (FSA) is used to study a 22‐year record of deep seismic tremor (30–60 km depth) for regions below Kilauea Volcano on the assumption that magma transport and fracture can be treated as a system of coupled nonlinear oscillators. Tremor episodes range from 1 to 100 min (cumulative duration = 1.60×104 min; yearly average = 727 min yr−1; mean gradient = 24.2 min yr−1 km−1). Partitioning of probabilities, pi, in the phase space of normalized durations, xi, are expressed in terms of a function f(α), where α is a variable exponent of a length scale, ℓ. Plots of f(α) vs. α are called multifractal singularity spectra. The spectrum for deep tremor durations is bounded by α values of about 0.4 and 1.9 at f = 0; fmax ≃ 1.0 for α ≃ 1. Results for tremor are similar to those found for systems transitional between complete mode locking and chaos.
Potential errors in locked mode synthetics for anelastic Earth models
Authors: Day Steven M. , McLaughlin Keith L. , Shkoller Boris , Stevens Jeffry L.
Published: February 2008

The method of mode superposition has been much applied in regional‐distance seismology to synthesize the complex seismic phases recorded in that distance range. As it is conventionally applied, however, this method can lead to significant errors in the calculation of regional seismic phases. The errors follow from the manner in which perturbation theory is employed to accommodate anelastic losses, and specifically from the use of the unperturbed (elastic) eigenfunctions to compute the mode residues for the anelastic problem. Resulting inaccuracies are most likely to be important when the intrinsic quality factors are strongly depth dependent. For a fairly realistic velocity and Q model of the Basin and Range, for example, mode superposition synthetics for an explosion source underestimated Pn and Pg amplitudes by about a factor of 2.
A predicted Triton plasma torus in Neptune's magnetosphere
Authors: Delitsky Mona L. , Eviatar Aharon , Richardson John D.
Published: February 2008

We investigate the possibility of the formation of a plasma torus generated by the satellite Triton in the magnetosphere of Neptune. We solve a set of coupled differential equations that describe the evolution of material sputtered from the surface or atmosphere of Triton in the conditions likely to exist in an assumed Neptunian magnetosphere for various combinations of nitrogen and methane that may exist on Triton. The model assumes a mechanism for transport that gives upper limits for predicted torus concentrations. Our conclusion is that a successful detection of plasma by the Voyager Plasma Science instrument may be possible and could be an important source of information about the composition of Triton's surface and atmosphere.
Reflection and refraction by tilted layers: An explanation for VHF auroral backscatter at large aspect angles
Authors: Moorcroft D. R.
Published: February 2008

Auroral structures are often accompanied by tilts to the electron density contours on the underside of the E‐region. By including the effects of these tilts on radio wave refraction and reflection it is possible to understand many of the previously puzzling observations of VHF auroral backscatter at large angles away from perpendicularity to the earth's magnetic field. It is shown that many of the characteristics of echoes from the VHF Canadian Bistatic Auroral Radar System (BARS) are consistent with this process. For BARS observations for which the tilt hypothesis is correct, the resulting Doppler velocities can be interpreted in the same way as those from STARE, and used to give electric fields and convection patterns over the BARS field of view.
A directional analysis of the small wavelength geoid in the Pacific Ocean
Authors: Moriceau Christophe , Fleitout Luce
Published: February 2008

The geoid over the Pacific Ocean has been filtered in order to enhance wavelengths of the order of 200 km. As noticed by previous authors, lineations elongated in the direction of present plate motion are observed in the East‐Central Pacific. Elongated features as clearly visible with a larger amplitude and a totally different direction are also present south of the Hawaiian chain and west of Baja California. The dominant directions visible on the filtered geoid map have been confirmed by spectral analyses. Near the Californian coast, the NE‐SW lineations seem to be related to extensional tectonics. South of Hawaii, the NW‐SE directions correspond to the various directions of the Pacific plate prior to 40 Ma. Magmas implaced in the lithosphere over fixed convective plumes may be the source of these geoid lineations.
A new method for determining the long‐period component of the source time function of large earthquakes
Authors: Zhang Jiajun , Lay Thorne
Published: February 2008

Inversions of seismic body waves indicate that most large earthquakes involve spatial and temporal heterogeneity of the moment release, but seismic body waves usually lack sufficient bandwidth to constrain the long‐period component of the radiation. Analysis of long‐period surface waves and free oscillations can constrain the overall source duration and moment; however, most procedures assume simple trapezoidal or boxcar source‐time histories, inconsistent with the body wave complexity. We find that source‐time function complexity can affect long‐period surface waves sufficiently to impact estimates of the source moment tensor, rupture duration and centroid depth. We present a procedure to objectively determine the long‐period component of complex source‐time functions in which we directly utilize results from body wave analysis. The method is applied to two great normal fault events of June 22, 1977 (Tonga, Mw=8.2) and August 19, 1977 (Indonesia, Mw=8.5). Standard long period analysis procedures underestimate the total slip duration in both cases. The overall source process times of both earthquakes are longer than 120 s.
On the seasonal components of polar motion
Authors: Volland Hans
Published: February 2008

The excitation functions for the seasonal components (annual and semiannual) of polar motion are calculated based on the atmospheric antisymmetric Rossby‐Haurwitz wave (1;−3). The meridional structures of geopotential and horizontal wind of this wave are reasonable approximations of the quasi‐standing seasonally varying Rossby waves propagating within the westerly background wind. Both wind and pressure loading contribute to the seasonal components of polar motion. The calculated displacement vector of the annual component agrees well with the observations. The semiannual component, estimated to be smaller by a factor of about ten, is not inconsistent with the data.
Age dependence of skewness of magnetic anomalies above seafloor formed at the Pacific‐Kula Spreading Center
Authors: Petronotis Katerina E. , Gordon Richard G.
Published: February 2008

The skewness of magnetic anomalies corresponding to chrons 25 to 32r (56‐72 Ma) was investigated on 22 North Pacific profiles recording Pacific‐Kula spreading. From 172 estimates of skewness we find that it varies with age, with irregular scatter superimposed on a steady increase with age of 1.20±0.27°/m.y. Skewness differs significantly between anomalies differing in age by as little as a million years. An analysis of the errors in the skewness estimates indicates significant errors that are systematic for an anomaly of a given age, but varying irregularly with age. The significant increase with age of phase shift may reflect an increase with age of anomalous skewness, or the northward motion of the Pacific plate, or both. If it is due entirely to Pacific plate motion, and an age‐independent value of anomalous skewness of 14° found in prior studies is assumed, the rate of northward motion is 0.70±0.26°/m.y., four times faster than estimated from seamount paleomagnetic poles and paleolatitudes determined from sediment cores.
Source location of the smooth high‐frequency radio emissions from Uranus
Authors: Farrell W. M. , Calvert W.
Published: February 2008

The source location of the smooth high‐frequency (SHF) radio emissions from Uranus has been determined using a technique differing from those applied previously. Specifically, by fitting the signal dropouts which occurred as Voyager traversed the hollow center of the emission pattern to a symmetrical cone centered on the source magnetic field direction at the cyclotron frequency, a southern‐hemisphere (nightside) source was found at approximately 56° S, 219° W. The half‐angle for the hollow portion of the emission pattern was found to be 13°.
Anisotropy beneath 9 stations of the GEOSCOPE Broadband Network as deduced from shear‐wave splitting
Authors: Ansel Valérie , Nataf Henri‐Claude
Published: February 2008

Polarization of SKS, ScS and S waves has been analyzed on digital 3‐components seismograms recorded at 9 stations of the recently installed GEOSCOPE broadband network. Splitting was observed for about 15 records, and is interpreted as being due to seismic anisotropy beneath the stations. From every record, it is possible to retrieve the fast direction at the station, and the time difference between the fast and slow polarization directions. Some 30 observations of quasi‐linear S‐pulses also help constrain the direction of fast velocity. Synthetic seismograms were built to test the validity of the method used to retrieve the parameters of anisotropy. Typical time‐differences are about 1 sec, corresponding, for example, to a 80 km‐thick zone of perfectly oriented pyrolite. The fast directions obtained at 3 continental stations in America (Westford, Santa Cruz, Heredia), could be related to plate tectonic processes. On the other hand, the fast directions found in 3 oceanic islands (Kipapa, Papete, La Réunion) differ strongly from the oceanic plate velocity direction there.
Glacial isostasy and the interplay between upper and lower mantle lateral viscosity heterogeneities
Authors: Sabadini R. , Gasperini P.
Published: February 2008

From the analysis of sea‐level data near the centre of the former Fennoscandian ice sheet and the theoretical predictions of vertically and laterally stratified Earth models, we explore the extent to which lateral viscosity variations could have influenced the estimate of long term mantle viscosity. We follow a finite element scheme in cylindrical symmetry, focusing on the effects of lateral viscosity contrasts of different magnitudes and wavelengths. Sea‐levels are consistent with long wavelength lateral viscosity contrasts of at most 2 orders of magnitude; short wavelength variations, comparable with the lateral extension of the surface load, should be ruled out. Differences in the average viscosities inferred from laterally stratified and uniform mantle models, may be as high as 1 order of magnitude. If we allow for different lateral viscosity patterns in the upper and lower mantle, we find that sea‐levels are consistent with short wavelength variations in the upper mantle of around 2 orders of magnitude, coupled with smoother lateral viscosity contrasts in the lower mantle.
Lateral variations in upper mantle thermal structure inferred from three‐dimensional seismic inversion models
Authors: Yan Ben , Graham E. K. , Furlong K. P.
Published: February 2008

Global shear wave velocity variations in the upper mantle (Woodhouse and Dziewonski, 1984) are employed as a basis for inferring lateral heterogeneities in temperature or composition at a depth of 150 km. Using experimentally determined elastic moduli for the olivine solid solution and Hashin‐Shtrikman bound theory, Vs and its partial derivatives with respect to temperature or composition (iron content) are calculated for the depth of interest. Based on these results, the observed seismic Vs variations are interpreted as temperature and compositional deviations relative to a spherically symmetric reference model.

If it is assumed that the Vs variations primarily represent lateral temperature changes, then the present results can be used to construct a global surface heat flow map from the geotherm families of Pollack and Chapman (1977). Our inferred heat flow patterns, calculated independently of actual heat flow data, show clear agreement with the surface heat flow maps proposed by Chapman and Pollack (1975) and Chapman (1985). This result is consistent with and supports thermal structure as the primary governing factor in the generation of upper mantle lateral velocity variations. Compositional changes appear to correlate with temperature, but affect velocity structure to a lesser extent.
Examination of stratospheric ozone photochemistry in light of recent data
Authors: Natarajan Murali , Callis Linwood B.
Published: February 2008

We examine in this paper the consistency of stratospheric ozone photochemistry using data from ATMOS and LIMS experiments. The ATMOS experiment measured vertical profiles of important trace constituents and temperature in the stratosphere during 1985. These observations have been used to constrain the levels of odd nitrogen and odd chlorine in a photochemical model. This model using current recommendations for the photochemical data yields O3 mixing ratios that are in good agreement with the observations. The deviation in ozone is less than 20% except near 52 km. The updated model has also been used in conjunction with the LIMS data to simulate the stratospheric photochemistry corresponding to the 1979 time period.
Frequency‐dependent refraction and multipathing of 10–100 second surface waves in the western Pacific
Authors: Lerner‐Lam Arthur L. , Park Jeffrey J.
Published: February 2008

We use a multi‐taper spectral estimation procedure to measure the frequency dependence of particle motion polarizations of long‐ and intermediate‐period fundamental mode Rayleigh and Love waves propagating across the thermally mature northwestern Pacific. Frequency‐dependent polarization parameters are measured for separated time windows for direct body phases, surface wave Airy arrivals, and early and late surface wave coda. The multi‐taper method has optimum spectral leakage properties for short time windows and supplies a framework for computing error estimates for polarization parameters. Our initial results show that surface waves between 10 and 100 mHz are strongly refracted by lateral heterogeneity in the northwestern Pacific. The frequency dependence of this refraction appears to be relatively simple.
Influence of heating mode on three‐dimensional mantle convection
Authors: Bercovici D. , Schubert G. , Glatzmaier G. A.
Published: February 2008

Numerical models of three‐dimensional, thermal convection in highly viscous spherical shells with different combinations of internal and basal heating consistently have upwelling concentrations in the form of cylindrical plumes and downwelling in planar sheets. As the proportion of internal heating increases, the number of upwelling plumes increases, and downwelling sheets become more vigorous and time‐dependent. With any amount of basal heating, the entire convective pattern, during its evolution, is anchored to the upwelling plumes. As the proportion of internal heating increases, the heat flow carried by the upwelling plumes remains a large fraction of the basal heat flow. Downwelling sheets carry only a minor fraction (approximately 30%) of the basal heat flow (even when the shell is entirely heated from below), but they advect almost all of the internally generated heat. The relatively large number of plumes in the Earth's mantle (inferred from hotspots), the possibility that downwelling slabs are vigorous enough to penetrate the lower mantle, and the small fraction of terrestrial surface heat flow carried by plumes all suggest that the mantle is predominantly heated from within.
A quiescent magnetosphere for Neptune
Authors: Dessler A. J. , Sandel B. R.
Published: February 2008

If Neptune has a large magnetic moment, a weak supply of plasma for its magnetosphere, and a magnetic moment that is in near alignment with the planetary spin axis, we argue that, except for a region near the magnetopause, the Neptunian magnetosphere is almost completely quiescent. Because the inner portion of a magnetosphere tends to be shielded from solar‐wind influences, a large magnetosphere would have all latitudes shielded except for a small polar region. If, for example, the equatorial magnetic field at cloudtop levels Bo were as large as, say, Jupiter's (4.2 Gauss), and if plasma pressure within the magnetosphere were negligible, the nominal nose distance Rm of the magnetosphere would be 74 RN. The shielded region could extend out to 25 RN, which corresponds to a magnetic latitude of nearly 80°. Rm varies as Bo1/3, so the size of the magnetosphere is not very sensitive to the strength of the planetary magnetic field. Also, typical variations in solar‐wind ram pressure do not cause large changes in the size of such a magnetosphere because Rm varies as the 6th root of the ram pressure. Standard magnetospheric theory promises that Neptune is a rotationally dominated magnetosphere, so the solar wind is not an effective power source. Zonal wind can contribute to energization of trapped radiation if the dipole is tilted relative to the spin axis. If Neptune's ionosphere and Triton's atmosphere together do not supply more than about 1 kg/sec to the magnetosphere, then, with a spin‐axis‐aligned dipole, the internal power sources for the magnetosphere would be less than 109 Watts (less than 1% of the average power utilized by the Earth's magnetosphere). This is consistent with the thus far observed lack of radio and auroral UV emissions. In such a magnetosphere, because they would enjoy a long residence time, non‐relativistic particles could collect to form a substantial radiation belt.
Grain metamorphism in polar nitrogen ice on Triton
Authors: Zent Aaron P. , McKay Christopher P. , Pollack James B. , Cruikshank Dale P.
Published: February 2008

We calculate the rate of nitrogen grain growth on putative N2‐rich polar caps on Triton. For most plausible assumptions of independent variables, mean grain sizes in polar N2 are meter‐scale. Triton's polar caps should constitute the definitive solar‐system test bed for the process of ice grain metamorphism. Interpretation of data already in hand may require long path length through condensed N2, possibly due to grain growth. Upcoming Voyager data may clarify the situation, although possible complications in detecting a glaze of N2 ice exist.
Triton: Scattering models and surface/atmosphere constraints
Authors: Thompson W. Reid
Published: February 2008

Modeling of Triton's spectrum indicates a bright scattering layer of optical depth τ ≃ 3 overlying an optically deep layer of CH4 with high absorption and little scattering. UV absorption in the spectrum indicates τ ≃ 0.3 of red‐yellow haze, although some color may also arise from complex organics partially visible on the surface. An analysis of this and other (spectro) photometric evidence indicates that Triton most likely has a bright surface, which was partially visible in 1977–1980. Geometric albedo p = 0.62−0.12+0.18, radius r = 1480 ± 180km, and temperature T = 48 ± 6 K. With scattering optical depths of 0.3–3 and ∼ 1–10mb of N2, a Mars‐like atmospheric density and surface visibility pertain. Imaging with the 0.62 µm CH4 filter of the Voyager 2 wide angle camera could show ∼20% contrast between the average surface and clean exposures of CH4 ice (which is not limited to the polar caps). Low far‐infrared atmospheric opacity will in principle allow the detection of thermal gradients in the surface caused by optically transmitting but infrared opaque CH4 and N2 ice.
Plasma ion heating of an SO2 atmosphere on Io
Authors: Johnson R. E.
Published: February 2008

The Jovian plasma ion heating of any atmospheric gas over Io is shown to be important for determining the temperature structure and the location of the exobase and for limiting diffusive separation in Io's atmosphere. This is used, along with the plasma supply rate, to estimate an average column of gas over the trailing hemisphere of ˜ 3 × 1016 SO2/cm² with exobase at ˜ 1.4 RIo.
Organic nitrates in remote marine environments: Evidence for long range transport
Authors: Atherton Cynthia S.
Published: February 2008

This paper examines both in‐situ production and long‐range transport of urban air as sources of marine alkyl nitrates. It is shown that alkyl nitrates are produced fairly rapidly in urban settings and persist for long times. The transport from urban areas can lead to alkyl nitrate concentrations of 4‐83 pptv after 120‐240 hours. These levels are far higher than those possible from marine in‐situ production. Additionally, alkyl nitrates may be more abundant than PAN in remote marine environments.
Elevation changes and the Great 1960 Chilean Earthquake: Support for aseismic slip
Authors: Linde Alan T. , Silver Paul G.
Published: February 2008

We reanalyse the near‐field vertical displacement data for the great Chilean earthquake of 1960 to provide constraints on the down‐dip slip distribution. A recent study of free oscillation data confirms earlier proposals of a slow precursor comparable in size to the main shock; we seek evidence for this event in the displacement data. Spatial coverage of the data is inadequate to allow determination of a unique fault model, but inversions show that thrust slip must extend over a width of about 300 km and to a depth between 60 km and 85 km, well below the seismogenic zone for interplate events. We propose that this deeper slip is the source of the slow event. Our preferred class of solutions has moments ranging from 1.6 × 1023 N m to 2.5 × 1023 N m, only 30% to 45% of the free oscillation value. Underestimation of the near trench displacements by 50% together with a seismic overestimation of moment by 30% due to tradeoff with rise time would result in satisfactory agreement.
Compression of tetrahedrally bonded SIO2 liquid and silicate liquid‐crystal density inversion
Authors: Stixrude Lars , Bukowinski Mark S. T.
Published: February 2008

We have investigated the response to pressure of liquid SiO2 by performing a quantitatively realistic Monte Carlo simulation. The model liquid was restricted to at most four‐fold Si‐O coordination by the effective imposition of an infinite potential barrier to a fifth bond. We thus obtained an unambiguous comparison of the compression mechanisms of solid and liquid tetrahedral networks. In spite of this restriction, the density of the simulated liquid exceeds that of the corresponding models of quartz, coesite and cristobalite at high pressure. The efficient compression of the liquid results from a continuous restructuring of the network that leaves the mean Si‐Si distance virtually unchanged and does not require an increase in the coordination number. The restructuring is effected by local breaking and reconnecting of bonds, a mechanism that is not available to a perfect crystal.
A re‐examination of impulsive VLF signals in the night ionosphere of Venus
Authors: Russell C. T. , Singh R. N.
Published: February 2008

Singh and Russell (1986) reported that impulsive electrical signals observed by the Pioneer Venus Orbiter Electric Field Detector at all frequencies clustered about periapsis. However, the impulsive signals consist of both signals entering the instrument through the antenna and artificial pulses associated with telemetry errors as Taylor and Cloutier (1988) have pointed out. Obvious telemetry errors were not included in the original study but records of which signals were thought to be naturally occurring and which were thought to be telemetry noise were not kept. Thus we cannot check the original identifications on a point‐by‐point basis. We can, however, repeat the study and compare statistical results. This study indicates that there is naturally occurring noise in the dark ionosphere of Venus near periapsis as originally reported by Singh and Russell. However, the absolute rates of occurrence of the original study and the present work differ. Sometimes the rates are smaller and sometimes larger than originally reported. These differences may be due to the use of a higher threshold in the earlier study together with the lack of sufficient discrimination against telemetry dropouts. Our rates of “naturally occurring” emissions also differ from the non‐spike noise rates obtained by Taylor and Cloutier although our rates of artificial signals are similar. In any event the Singh and Russell study should not be used to infer the altitude distribution of the noise since the spacecraft spends more time at low altitude than high as it traverses the dark ionosphere.
A mid‐latitude balloon‐borne observation of total odd nitrogen
Authors: Kondo Y. , Aimedieu P. , Matthews W. A. , Sheldon W. R. , Benbrook J. R.
Published: February 2008

A balloon‐borne instrument to measure total odd nitrogen (NOy) has been developed. A converter which enables catalytic conversion of NOy into nitric oxide on a heated gold surface is combined with a chemiluminescence detector. The conversion efficiency for nitrogen dioxide was measured to be close to 100% at pressures between 60 and 7 mb. The major source of errors in the balloon‐borne measurements are the uncertainties in the estimates of the sample flow rate and the zero level of the instrument. The NOy concentration was measured at altitudes between 12 and 28 km with a precision of about 25% on a balloon experiment conducted at latitude 44°N in June, 1989. The NOy concentration has been measured to be 1.5±0.4, 3±0.7, 10±3, and 14±4 ppbv at altitudes of 17, 20, 25, and 28 km, respectively. This was the first in situ NOy measurement in the stratosphere above 20 km.
Ozone and temperature profiles over Mcmurdo Station Antarctica in the spring of 1989
Authors: Deshler T. , Hofmann D. J. , Hereford J. V. , Sutter C. B.
Published: February 2008

Ozone and temperature were measured in 39 balloon soundings at McMurdo station Antarctica (78°S) in the spring of 1989. Compared to 1986 and 1988 the stratosphere was colder and ozone depletion worse. Compared to 1987 the stratosphere warmed earlier but ozone depletion was similar, both in the magnitude and rate of depletion. Within regions of the atmosphere in 1989 ozone depletion was between 80 and 98% complete. This was again similar to 1987 and suggests that conditions observed in 1987 exceeded the minimum required for rapid and complete ozone depletion. As in previous years ozone was destroyed primarily between 12 and 20 km and there were several short periods, < 5 days, when rapid depletion was observed.
Precise regional baseline estimation using a priori orbital information
Authors: Lindqwister Ulf J. , Lichten Stephen M. , Blewitt Geoffrey
Published: February 2008

A solution using GPS measurements acquired during the CASA UNO campaign has resulted in 3–4 mm horizontal daily baseline repeatability and 13 mm vertical repeatability for a 729 km baseline, located in North America. The agreement with VLBI is at the level of 10–20 mm for all components. The results were obtained with the GIPSY orbit determination and baseline estimation software and are based on five single‐day data arcs spanning the 20, 21, 25, 26, and 27 of January, 1988. The estimation strategy included resolving the carrier phase integer ambiguities (bias fixing), utilizing an optimal set of fixed reference stations (fiducials), and constraining GPS orbit parameters by applying a priori information (derived from initial multi‐day trajectory fits to broadcast ephemeris data). A multi‐day (January 20–27) GPS orbit and baseline solution has yielded similar 2–4 mm horizontal daily repeatabilities for the same baseline, consistent with the constrained single‐day arc solutions. The application of weak constraints to the orbital state for single‐day data arcs produces solutions which approach the precise orbits obtained with unconstrained multi‐day arc solutions. This work suggests that the general availability of nominal ephemerides based on many days of global tracking data would be very valuable and practical for regional geodesy, allowing for high precision with single‐day network solutions when combined with a continental scale fiducial network.
Suprathermal ion fluxes in the plasma sheet
Authors: Baumjohann W. , Sachsenweger D. , Möbius E.
Published: February 2008

About 14,000 measurements of the three major suprathermal ion species, H+, O+, and He++, in the Earth's plasma sheet are compared for differences in the ion fluxes between the central plasma sheet and the plasma sheet boundary layer as well as between magnetically quiet and disturbed intervals. The H+ and He++ spectra are nearly identical in both regions as well as during quiet and disturbed times, except for the absolute flux levels. The O+ spectra are always considerably harder. The spectral shapes of all three ion species and their relative abundances do not change between central plasma sheet and plasma sheet boundary layer; there is merely a difference in the flux levels. Substorms affect the suprathermal ions in the central plasma sheet in the same way as those in the plasma sheet boundary layer: their spectra get considerably harder, but the relative abundances of the higher mass ions decrease. The ratios of the ion fluxes during disturbed intervals to those during quiet times are best ordered in energy per charge and nearly identical in both regions.
Stratospheric temperatures during the 88–89 Northern Hemisphere winter
Authors: Newman Paul A. , Lait Leslie R. , Schoeberl Mark R. , Nagatani Ronald M.
Published: February 2008

The Airborne Arctic Stratospheric Expedition (AASE) was conducted during January and February 1989. The polar stratosphere during this period was characterized by cold conditions from January to mid‐February. A mid‐February wave 2 major warming considerably warmed the polar stratosphere, but did not immediately lead to a lower stratospheric vortex breakup. As inferred from temperature data, January temperatures were sufficient for polar stratospheric cloud (PSC) formation. PSC regional extent was greater than the long‐term average, but not significantly larger than in previous years.
Radiative heating rates during the Airborne Arctic Stratospheric Experiment
Authors: Rosenfield Joan E. , Schoeberl Mark R. , Lait Leslie R. , Newman Paul A. , Proffitt Michael H. , Kelly Ken K.
Published: February 2008

A radiative transfer model and observed temperature and ozone profiles are used to compute three dimensional fields of heating rates for the Northern Hemisphere during the 1989 Airborne Arctic Stratospheric Experiment. For a clear atmosphere, an average cooling of 0.2 to 0.4 K/day is computed in the regions of the ER‐2 aircraft during flight days. Tropospheric clouds will increase the cooling by 0.1 to 0.2 K/day. These cooling rates are in good agreement with the diabatic cooling estimated from N2O data. Net heating rather than cooling is computed in tie area of the ozone “minihole” which had its maximum on 1/31/89 and 2/1/89 in the vicinity of the mission. On 1/31/89 the 50 and 30 mb net heating rates are 0.1 to 0.2 K/day for clear skies, and 0.05 to 0.1 K/day for cloudy skies.
Measurement of the condensation nuclei profile to 31 km in the Arctic in January 1989 and comparisions with Antarctic measurements
Authors: Hofmann D. J.
Published: February 2008

The first measurement of the condensation nuclei (CN) profile in the Arctic during winter was made to 31 km on 30 January 1989 from Kiruna Sweden (68° N). Enhanced levels of CN were observed in the colder regions above 18 km suggesting homogeneous or ion nucleation of CN as observed previously in Antarctica. A CN layer reaching a concentration of about 40 cm−3 was observed between 22.5 and 26 km. Comparisons with data obtained in Antarctica in 1987 and 1988 indicate that this layer is similar to those observed at the same altitude in Antarctica under similar solar illumination conditions. The latter are believed to be of photochemical origin as suggested by measurements before and after stratospheric sunrise. This CN layer may thus serve as a measure of the amount of time an air parcel has spent in sunlight, an important parameter during the early stages of spring ozone depletion.
Optical backscatter characteristics of Arctic polar stratospheric clouds
Authors: Kent G. S. , Poole L. R. , McCormick M. P. , Schaffner S. K. , Hunt W. H. , Osborn M. T.
Published: February 2008

Airborne lidar measurements have been made of polar stratospheric clouds (PSCs) during the Airborne Arctic Stratospheric Expedition in January–February 1989.These show the existence of a systematic relationship between the backscatter depolarization ratio, δ, and the (aerosol + molecular)/molecular backscatter ratio, R.The data are consistent with a two population PSC particle model. The first population consists of particles with low values for δ (≤ 0.02) and low to intermediate values for R (≤ 6). The second population is characterized by higher values for δ (up to 0.60) and R (up to 40 or greater). The relationship between δ and R, observed within a limited range of altitudes and latitudes, corresponds to a mixture of the two populations with variable concentrations but constant optical properties.
Arctic polar stratospheric cloud observations by airborne lidar
Authors: McCormick M. P. , Kent G. S. , Hunt W. H. , Osborn M. T. , Poole L. R. , Pitts M. C.
Published: February 2008

Lidar observations obtained from January 24 to February 2, 1989, during the Airborne Arctic Stratospheric Expedition (AASE) mission further support the existence of two distinct classes (Types 1 and 2) of polar stratospheric clouds (PSCs). Most of the Type 1 PSCs observed were formed by rapid adiabatic cooling and exhibited very low depolarization ratios and low‐to‐intermediate scattering ratios. Type 2 PSCs were observed in regions of lowest temperature and showed much larger depolarization and scattering ratios, as would be expected from larger ice crystals. PSCs with low scattering ratios but moderate depolarization ratios were observed near the center of the vortex on one flight. These may have been either sparse Type 2 PSCs or Type 1 PSCs formed by less rapid cooling.