bluuebunny/crossref_metadata_2025 huggingface dataset:
The origin of the power‐law component in auroral electron spectra
Authors: Stasiewicz K. , Lundin R. , Hultqvist B.
Published: February 2008

Electron and ion data from the particle experiment onboard the VIKING spacecraft are examined in order to determine the origin of the power‐law component in auroral electron spectra. It is observed that at altitudes of ≈1 Re electron spectra peaked at a few keV are accompanied by a power law population in the energy range 10‐1000 eV that is usually thought to be composed of degraded primaries and secondary electrons of ionospheric origin.

However, the presence of an ion beam at an energy of 1 keV flowing out of the ionosphere indicates the existence of a potential barrier between the location of the satellite and the ionosphere which would prevent secondary electrons of ionospheric origin from reaching the satellite altitude. Moreover, the angular characteristics of the low energy electrons indicate that this population moves downward and cannot be attributed to secondary and backscattered electrons coming out of the ionosphere. The spectral index k=1.7‐2 of the distribution function f ⧜ E−k for the power‐law electrons supports earlier theoretical findings that this population is formed in the auroral acceleration region by a combined action of a parallel electric field and waveparticle interactions.
Observations of ion cyclotron harmonic waves by the Viking satellite
Authors: Koskinen H. E. J. , Kintner P. M. , Holmgren G. , Holback B. , Gustafsson G. , André M. , Lundin R.
Published: February 2008

During the first months of operation the Swedish magnetospheric satellite Viking has detected many examples of plasma waves with spectral features ordered by the proton gyro frequency. Even though the proton gyro frequency characterizes all such spectra, there are many variations from spectrum to spectrum. Different bands are excited and the emissions are located within different parts of the harmonic bands at different times; sometimes a little above the harmonics, sometimes slightly below, and sometimes in the middle of the bands. The amplitudes of the waves are small, on the order of 1 mV/m, often less. Some of these waves do not appear to have been previously reported and we present here a representative example that took place at an altitude of about 13000 km on geomagnetic field lines connected to morning side auroral oval. The generation mechanism is still uncertain but simultaneously measured particle data indicate that there is free energy available in the loss cone in the hot ion population. If the loss cone is the source of free energy, these waves are of importance for proton precipitation in diffuse aurora.
Rotated oceanic blocks in western Ecuador
Authors: Roperch P. , Mégard F. , Laj C. , Mourier T. , Clube T. M. , Noblet C.
Published: February 2008

A paleomagnetic study of over 250 cores from 21 sites sampled over a distance exceeding 250 Km in the early Cretaceous Pinon formation in the Costa of Western Ecuador indicates that the sampled lithologies (essentially MORB‐type basalts and dolerites) carry a stable remanent magnetization, whose direction significantly deviates from that of coeval formations of stable South America. Although both normal and reverse directions have been recorded, the two polarities cannot easily be distinguished because of the low latitude of the ocean floor at the time of formation. The most likely interpretation is that the entire area has undergone 70° clockwise rotation since its genesis. These results thus yield new evidence for an allochtonous origin of this suspect terrane.
Observations of the decay of the El Chichon stratospheric aerosol cloud in Antarctica
Authors: Hofmann D. J. , Rosen J. M. , Harder J. W. , Rolf S. R.
Published: February 2008

Balloonborne measurements of stratospheric aerosol in the late October ‐ early November period in 1983, 1984 and 1985 indicate that the sulfuric acid aerosol which formed in the stratosphere following the eruption of El Chichón in 1982, and which was subsequently transported to the polar regions, decayed over Antarctica with an exponential decay time of about one year, in reasonable agreement with extensive measurements at Laramie during this period. These results suggest that the increased aerosol burden over Antarctica, which occurred as a result of the El Chichón eruption, cannot be directly involved in the precipitous decline of stratospheric ozone in Antarctica since 1982, although indirect effects cannot be ruled out.
Quantification of HCl from high resolution infrared solar spectra obtained at the South Pole in December 1986
Authors: Goldman A. , Murcray F. J. , Murcray F. H. , Murcray D. G.
Published: February 2008

Ground‐based infrared solar spectra at 0.02 cm−1 resolution obtained at the Amundsen‐Scott South Pole station in December 1986 have been analysed for the atmospheric content of HCl. Nonlinear least‐squares spectral fitting applied to the spectra yields a total HCl column amount of (6.4 ± 0.8) × 1015 molec/cm², most being stratospheric. This amount is larger than that extrapolated from earlier results on the latitudinal distribution of atmospheric HCl.
Consequences of experimental transient rheology
Authors: Sabadini Roberto , Smith Brad K. , Yuen David A.
Published: February 2008

Recent analyses of transient creep data for lower crustal and upper mantle substances show that the parameters of the Burgers’ body rheological model, used up to now by geodynamicists, have much lower ratios of the short‐term to long‐term viscosities than the laboratory values. We have used these data to constrain the viscosity contrast across the 670 km discontinuity. Our results show that the previously inferred viscosity variations are now reduced by about a factor of ten in the new transient models. This finding is in agreement with the revised viscosity estimate based on long‐wavelength geoid anomalies and seismic tomography. We find that time‐dependent perturbations to the gravity field from recent ice movements are not at all small.
Solar flare perturbations in stratospheric current systems
Authors: Holzworth R. H. , Norville K. W. , Williamson P. R.
Published: February 2008

Electric field, conductivity, and ionization rate data were collected on two balloon payloads at 26 km in the southern hemisphere stratosphere during the solar flare of 16 February 1984. Both polarities of the conductivity were enhanced by a factor of two at a payload with an invariant latitude (Λ) of −56.3° (Rigidity = 1.4GV). At the same time no transient effects were seen in any of these parameters by a more equatorially located payload at Λ = −48.8° (Rigidity = 2.8 GV). The two payloads were separated by 5 hours of local time. The vertical current density (Jz) at the poleward most payload was enhanced by over a factor of two, while no Jz variations were seen by the equatorward payload. Interpretation of these observations suggests that a simple RC time constant analysis of the global circuit may be incorrect.
Observations of free oscillation amplitude anomalies
Authors: Pollitz Fred F. , Park Jeffrey , Dahlen F. A.
Published: February 2008

In a frequency domain analysis of long‐period seismic data, observations of free oscillation excitation amplitudes are required in addition to frequency shifts to constrain odd‐degree aspherical earth structure. To determine the feasibility of incorporating such data into large‐scale inversions, we have undertaken a preliminary analysis of the observed amplitudes of fundamental spheroidal mode multiplets oSl with 26 ≤ l ≤ 43 using seismograms recorded by the IDA network. For many records, the amplitudes may be significantly better fit by allowing for a systematic shift of the theoretical spherical earth nodal lines either toward or away from the epicenter. In the great‐circular geometrical optics approximation, this spatial phase shift of the amplitude pattern can be asymptotically represented in terms of the minor arc integral of δωlocal — along the source‐receiver path. Results from common source‐receiver paths indicate consistent sampling of the structure underlying these paths. For a number of paths, the results differ significantly from the theoretical predictions of model M84A of Woodhouse and Dziewonski.
A procedure for the joint inversion of regional and teleseismic long‐period body waves
Authors: Holt William E. , Wallace Terry C.
Published: February 2008

A procedure for the joint inversion of regional and teleseismic long‐period waveforms for source parameters is presented. Three test cases demonstrate that the inclusion of regional distance seismograms to a data set of teleseismic observations stabilizes the inversion process and adds valuable constraints to the source parameter estimates, particularly when the teleseismic Green's functions are inadequate. The added stability and constraints from regional waveforms can be attributed to the robust nature of regional distance Green's functions, as well as the added coverage of the focal sphere that regional data provide. Singular value decomposition is a useful inversion method that is well suited for this study because it provides a measure of the solution dependence on individual observations.
The effects of rainfall upon geothermal springs, Rotorua, New Zealand
Authors: Turner G. J.
Published: February 2008

A previous empirical analysis of rainfall to January 1983 at Rotorua led to a deduction that periods of low rainfall preceded temporary cessations of geothermal springs in 1924 and 1943 by about 8 years. That analysis is shown here to approximate flow from a spring fed by a leaky reservoir. Upon adding recent rainfall an additional minimum of pressure in such a reservoir is seen to have occurred in 1983‐85. With the deduced 8‐year response, a natural decline in the spring flow would thus be expected in 1991‐93. Using this spring‐reservoir model, minima of flow are indeed apparent in 1924 and 1943, and there is a downward trend to the present.
Magnetic reconnection in a collisionless plasma: Evidence for the current sheet acceleration
Authors: Lee L. C. , Ding D. Q.
Published: February 2008

The magnetic reconnection process in a collisionless plasma is studied based on a particle simulation. It is found that the magnetic field reversal and particle energization take place mainly in the midplane of the outflow region and the particle acceleration by slow shocks is not important. This result is consistent with the collisionless reconnection model proposed by Hill [1975].
Waveform inversion using secondary observables
Authors: Cara M. , Lévêque J. J.
Published: February 2008

A new method is proposed for inverting single‐station surface‐wave seismograms. Instead of inverting directly the time‐signal, use is made of secondary observables built up from a set of time‐frequency images. This allows us to enhance the signal‐to‐noise ratio and to make more linear the relationship between the model parameters and the inverted observables. The feasibility of the method is checked on multimode synthetics prior to present the inversion of a long‐period multimode seismogram related to the Pacific Ocean.
Bomb radiocarbon in metabolically inert tissues from terrestrial and marine mammals
Authors: Bada Jeffrey L. , Vrolijk Christian D. , Brown Stephen , Druffel Ellen R. M. , Hedges Robert E. M.
Published: February 2008

We report here radiocarbon measurements of monkey eye lens nucleus proteins and a narwhal tusk, biological tissues which have sampled the bomb radiocarbon signal in different ways. The results confirm the metabolic inertness of eye lens nucleus proteins and demonstrate the feasibility of measuring radiocarbon in small samples of biological tissue using accelerator mass spectrometry (AMS). The narwhal tusk provides a unique record of the radiocarbon activity in Arctic Ocean waters over most of the 20th century.
Electrical conductivity of (Mg,Fe)SiO3 perovskite and a perovskite‐dominated assemblage at lower mantle conditions
Authors: Li Xiaoyuan , Jeanloz Raymond
Published: February 2008

Electrical conductivity measurements of perovskite and a perovskite‐dominated assemblage synthesized from pyroxene ((Mg0.88Fe0.12)SiO3) and olivine ((Mg0.88Fe0.12)2SiO4) demonstrate that these high‐pressure phases are insulating to pressures of 82 GPa and temperatures of 4500 K. Assuming an anhydrous upper mantle composition, our result provides an upper bound of 10−2 S m−1 for the electrical conductivity of the lower mantle between depths of 700 and 1900 km. This is 2 to 4 orders of magnitude lower than previous estimates of lower‐mantle conductivity derived from studies of geomagnetic secular variations.
Elastic interface waves along a fracture
Authors: Pyrak‐Nolte Laura J. , Cook Neville G. W.
Published: February 2008

Non‐welded interfaces can be treated as a displacement discontinuity characterized by elastic stiffnesses. Applying this boundary condition to a generalized Rayleigh wave, it is shown that a fast and a slow dispersive wave can propagate along the fracture, even when the seismic properties of the rock on each side are identical.
Nature of the lower crust and moho in eastern Nevada from “wide‐angle” reflection measurements
Authors: Valasek Paul A. , Hawman Robert B. , Johnson Roy A. , Smithson Scott B.
Published: February 2008

Wide angle recordings at offsets between 20 and 40 km in the Ruby Mountains consistently show 5 strong reflections between 4 and 11 s with enough moveout to estimate velocities to the base of the crust. The uppermost “layer” with a temperature corrected velocity of 6.2 km/s and thickness of 9 km corresponds to quartzofeldspathic rocks such as metasedimentary rocks, migmatites and deformed granites and is underlain by a 7‐km‐thick “layer” with velocities of 6.4 km/s which corresponds to quartzofeldspathic material interlayered with amphibolites. The lower crust consists of a heterogeneous, 9 km‐thick zone with velocities of 6.7 to 6.8 km/s corresponding to mafic rocks interlayered with smaller amounts of quartzofeldspathic rock. The lowermost crust is marked by the “X” reflection overlying a 3‐km‐thick “layer” with velocities between 7.4‐7.8 km/s corresponding to anomolous material, possibly layered cumulates. The subhorizontal, layered structure of the crust is caused primarily by ductile extension, which may well be superposed on material added to the crust by underplating. At most, approximately one third of the present crust could have been added by underplating in the Cenozoic.
The northern and southern auroral ovals in response to the IMF By component
Authors: Nakai H.
Published: February 2008

The auroral boundary in terms of precipitating electrons is used to examine the influence of the By component of the interplanetary magnetic field (IMF) on the size of the auroral oval. It is found that when the earth's dipole tilt angle is positive (negative), the size of the auroral oval during periods of positive By is smaller (greater) than that during periods of negative By, and that the dependence occurs in the same way in both the northern and southern hemispheres. This finding implies that the size of the auroral oval is controlled by dayside reconnection, the rate of which depends strongly on the IMF By component and the dipole tilt angle.
Mercury's magnetospheric irradiation effect on the surface
Authors: Ip W.‐H.
Published: February 2008

Using numerical model calculations, we investigate the transient heating effect from magnetospheric charged particle precipitation as proposed by Baker et al. (1987). Under extreme circumstances, the transient temperature increase may reach 1 K if the heating duration lasts more than one minute and the energy influx reaches 104 ergs/cm²/s. Otherwise, the expected temperature rise should be substantially smaller (ΔT < 0.05 K). From this point of view, optical observations capable of differentiating various degrees of particle irradiation effect (i.e., modification of optical properties of surface dust layer and/or regolith structure) might be more appropriate to pinpoint signature of Mercury's auroral zones.
Magnetic remanence measurements of single particles and the nature of domain patterns in titanomagnetites
Authors: Metcalf M. , Fuller M.
Published: February 2008

In addition to classical body domain patterns, a profusion of complex maze like domain structures have been observed using the Bitter technique on titanomagnetites. Controversy persists over how important a role such complicated domain patterns play in remanent magnetization. We have compared the magnetic properties of single particles, which exhibit complex patterns with those that exhibit simple ones. IRM acquisition and DC and AF demagnetization of IRMs of single particles were measured. We found that both types of grains exhibit similar bulk magnetic properties. The simple patterns reorganize with changing magnetization state while complicated patterns apparently remain constant. We suggest that the remanent magnetization of grains with complicated patterns is carried by the bulk of the particle within which a more simple domain structure controls magnetic behavior.
Neptune radio emission: Predictions based on planetary scaling laws
Authors: Desch Michael D.
Published: February 2008

In this paper a prediction is advanced concerning Neptune's low‐frequency radio emission based on the radiometric Bode's law for radio planets in combination with the magnetostrophic scaling law for magnetized planets. We expect the total emitted radio power to be about 1.6 × 107 W, very nearly the same as that predicted and observed for Uranus. Possible emission spectral shapes, based on Saturn and earth‐like models, are shown. Using these models, the radio emission frequency range is predicted to extend from approximately 100 to just over 1000 kHz, with a spectral peak between 350 and 500 kHz. If radiation is beamed approximately in the sunward direction, Neptune should be detectable by the planetary radio astronomy experiment onboard the Voyager spacecraft sometime between 45 and 90 days before closest approach. This detection is likely to represent the first direct evidence of a Neptune magnetic field. Possible implications for Neptune's magnetosphere with regard to the time of first detection are discussed.
Midlatitude ClO below 22 km altitude: Measurements with a new aircraft‐borne instrument
Authors: Brune Wm H. , Weinstock E. M. , Anderson J. G.
Published: February 2008

Midlatitude stratospheric ClO at altitudes below 22 km has been measured for the first time. Measurements were made at latitudes between 27°N and 48°N during three flights from Moffett Field, California, in June and July of 1987, with a new instrument flown on the NASA ER‐2 aircraft. The result from these flights is that the ClO mixing ratio increases from less than 0.5 pptv at 16.8 km to 2.0 pptv at 18.3 km and 10.1 pptv at 21 km. These altitude profiles agree with an extrapolated profile from our May 1986 balloon‐borne experiment.
Evidence of heavy positive ions at the summer Arctic mesopause from the EISCAT UHF incoherent scatter radar
Authors: Collis P. N. , Turunen T. , Turunen E.
Published: February 2008

A confined layer characterised by narrow incoherent scatter spectra has been observed between 86 and 88 km altitude in the high latitude summertime D‐region with the EISCAT radar. Properties of the background plasma inferred from spectral measurements outside the layer are in close agreement with model predictions, but the localised minima in spectral width imply much heavier positive ions within the layer. This feature is interpreted as being due to the presence of large clustered ions with mass of the order of 500 amu, which are possibly hydrated protons with a mean hydration index of almost 30.
Eastward propagation of PC4‐5 range CNA pulsations in the morning sector observed with scanning narrow beam riometer at L=6.1
Authors: Kikuchi Takashi , Yamagishi Hisao , Sato Natsuo
Published: February 2008

A new type of cosmic noise absorption (CNA) pulsation is observed with a scanning beam riometer with a spatial resolution of 10 km, at Syowa station, Antarctica (L=6.1). This type of CNA pulsation has a short azimuthal wavelength (80–600 km), corresponding to a large azimuthal m‐number (20–180). Most CNA pulsations with a period of 1 to 10 min propagate eastward at a speed of 200 m/s to 3 km/s in the morning sector (5–10 MLT). The eastward propagation direction is opposite to that of CNA pulsations with a small m‐number as reported by Olson et al. (1980). The pulsation period tends to increase, while the propagation speed decreases with increasing local time. These results suggest that the source of this new type of CNA pulsation first appears in the nightside magnetosphere and moves toward noon. It is pointed out that the finding of this new CNA pulsation is due to the high spatial resolution (10 km) and narrow antenna beam (13°) of the scanning riometer system.
A new transient tracer: Measured vertical distribution of CCl2FCClF2 (F‐113) in the North Pacific Subarctic Gyre
Authors: Wisegarver David P. , Gammon Richard H.
Published: February 2008

The first quantitative marine measurements of trichlorotrifluoroethane (F‐113) were made in the North Pacific subarctic gyre in July of 1986, using a modification of the analytical procedure developed for the transient tracers F‐11 and F‐12 (Gammon et al., 1982; Wisegarver and Cline, 1985). The measured mixed layer concentration was 0.29±0.02 pM/L; the corresponding atmospheric mixing ratio was 35±1 pptv (Rasmussen scale).

Below a subsurface maximum both F‐11 and F‐113 were found to fall off exponentially with increasing depth, F‐113 reaching effective blank levels first. The significance of adding F‐113 to the existing suite of measurable oceanic transient tracers rests in the possibility of age‐dating water masses by their (F‐113/F‐11) ratio with near annual resolution for the period since 1977.
Excitation of N2 Lyman‐Birge‐Hopfield Bands emission by low Earth orbiting spacecraft
Authors: Kofsky Irving L.
Published: February 2008

The spectral distributions in the artefactual Lyman‐Birge‐Hopfield bands observed from the S3‐4 satellite and Spacelab 1 are shown to be consistent with excitative recombination of ground‐state N atoms catalyzed by spacecraft and instrument surfaces exposed to the atmosphere. This heterogeneous (and most probably Langmuir‐Hinshelwood) reaction is analogous to the homogeneous reactions that produce the well‐known VUV afterglow of active nitrogen. Promoting/interfering surface processes (perhaps involving conditioning) and undocumented systematic changes in vehicle orientation are among the possible causes of the strong dependence of the measured nadir system intensities on the ambient density of N(4S).
MM‐wave observations of stratospheric HCN at tropical latitudes
Authors: Jaramillo M. , de Zafra R. L. , Barrett J. W. , Parrish A. , Solomon P. M.
Published: February 2008

We have measured middle and upper stratospheric HCN using ground‐based mm‐wave emission spectroscopy, during a series of observations made in Mauna Kea, Hawaii, in June of 1986. We find a volume mixing ratio of 190±40 pptv at ∼40 km, and a decrease of concentration with altitude that is considerably slower than that predicted by current models. This could be an indication of an atmospheric source of HCN as yet unidentified.
Current sheet crossings in the distant magnetotail
Authors: Heikkila W. J.
Published: February 2008

A computer search of crossings of the field reversal region in the middle of the distant magnetotail has been done with ISEE‐3 data. We have found that the instantaneous direction of the magnetic field at the crossings Bz is northward on average at a distance of 220 RE, with moderate values of the plasma flow. This result suggests that the magnetic field lines are closed; since the flow is tailward, the Dungey model with a steady state reconnection line across the magnetotail earthward of the spacecraft is invalidated. Our result gives strong support to a model in which tailward boundary layer flow provides the viscous interaction proposed by Axford and Hines. At higher values of the plasma velocity we do find negative values of Bz, a result consistent with the existence and tailward motion of plasmoids; these can be created by a form of localized magnetic merging which is three dimensional and time‐dependent. The latter differs essentially from steady state reconnection in that here curl E plays a crucial role, as is obvious from a careful consideration of Poynting's theorem. This does not invalidate the denial of steady state reconnection.
A simple model describing the nonlinear dynamics of the dusk/dawn asymmetry in the high‐latitude thermospheric flow
Authors: Gundlach J. P. , Larsen M. F. , Mikkelsen I. S.
Published: February 2008

A simple nonlinear, axisymmetric, shallow‐water numerical model has been used to study the asymmetry in the neutral flow between the dusk and dawn sides of the auroral oval. Our results indicate that the Coriolis force and the curvature terms are nearly in balance on the evening side and require only a small pressure gradient to effect adjustment. The pressure gradient on the morning side has to balance both the Coriolis force and the curvature terms. The result is smaller neutral velocities near dawn and larger velocities near dusk than would be the case for a linearized treatment. A consequence is that more gravity wave energy is produced on the morning side than on the evening side.
On the statistical correlation between polar mesospheric cloud occurrence and enhanced mesospheric radar echoes
Authors: Jensen Eric J. , Thomas Gary E. , Balsley Ben B.
Published: February 2008

Using data from the Poker Flat MST radar and the Solar Mesosphere Explorer Satellite (SME), we demonstrate the existence of a statistically significant correlation between the occurrence of Polar Mesospheric Clouds (PMC) and enhanced VHF radar echoes near the high‐latitude summer mesopause. We propose three physical conditions which could explain the coexistence of strong summertime echoes and PMC. First, both the enhanced echoes and the PMC are most likely to occur in the presence of very low mesopause temperatures and associated steep temperature gradients. Second, the presence of PMC ice particles could induce a strong gradient in the electron density profile, which would produce enhancements in the radar echo strength. Third, it is likely that heavy water cluster ions, indicative of PMC particle nucleation, can alter the ambipolar diffusion coefficient, thus allowing the electron density fluctuations to extend down to much smaller vertical scales. Under these conditions, the turbulent power at the 3 meter scale required for the occurrence of the MST radar echoes could be greatly enhanced. Finally, we discuss the possibility of using MST radars as instruments for PMC detection.
Paleomagnetism of paleozoic asphaltic deposits in southern Oklahoma, USA
Authors: Ellwood Brooks B. , Crick Rex E.
Published: February 2008

Paleomagnetic measurements on asphaltic samples from two formations in southern Oklahoma have been performed. A bioclastic unit from the Boggy Formation, known as the Buckhorn asphalt, exhibited a stable, characteristic remanent moment (RM) after A.F. demagnetization between 5–20 mT. We infer from our data that very fine, possibly authigenic magnetite, like that shown to have a genetic relationship with the migration through rocks of hydrocarbons [Elmore et al., 1987], is the primary RM carrier in these samples. The tilt corrected paleopole for the Buckhorn asphalt (121.9 E; 43.5N; δp=1.3; δm=2.3) falls on the Early Permian Apparent Polar Wander Path for North America of Irving and Irving [1982], using a 30 Ma window (270–280 Ma). Because the Boggy Form‐ation, containing the Buckhorn asphalt, was depos‐ited during the Late Pennsylvanian (Desmoinesian), we interpret the data to indicate magnetization during minor uplift in the Early Permian of the Arbuckle Mountain region. The RM appears to have been acquired at this time, probably as the result of magnetite production facilitated by the introduction time of sulfate reducing bacteria.
High precision 40Ar/39Ar dating of Oligocene rhyolites from the Mogollon‐Datil Volcanic Field using a continuous laser system
Authors: Dalrymple G. Brent , Duffield Wendell A.
Published: February 2008

Replicate 40Ar/39Ar analyses of sanidine from seven Oligocene (28.2 Ma) rhyolite flows using a continuous laser dating system routinely yield analytical precisions of less than 0.45% (1s) on samples smaller than 0.5 mg. This is as good or better than has been obtained by any other method even though the sample mass is several orders of magnitude smaller. The system has the potential of resolving differences in apparent age of as little as 0.2% for high K/Ca samples as young as a few Ma. The analyses suggest that the seven volcanic units analyzed were erupted in an interval of about 0.1 m.y. or less.
An analysis of the effects of thermal demagnetization on magnetic carriers
Authors: Holm Eric J. , Verosub Kenneth L.
Published: February 2008

We have attempted to determine why samples of the Mio‐Pliocene Purisima Formation are not amenable to thermal demagnetization. Analyses of the changes in direction, intensity, susceptibility, color, and saturation magnetization as well as examination of individual magnetic grains using a scanning electron microscope have all contributed to the development of a consistent hypothesis for the fate of iron during thermal demagnetization. In this particular case, we believe that oxidation‐exsolution of ilmenite and then direct dissolution of nearly pure magnetite result from progressively higher heating levels. Our approach should be useful in understanding the origin and nature of the magnetization of many lithologies, including those for which thermal demagnetization is the method of choice.
A synthetic TRM induction curve for fine particles generated from domain observations
Authors: Metcalf M. , Fuller M.
Published: February 2008

A synthetic thermoremanent magnetization (TRM) induction curve is produced from domain observations of an ensemble of pseudosingle domain (PSD) titanomagnetite particles in oceanic basalts. The observations were made after the samples were given a TRM in fields of 0.1, 2, 4, 6, and 8mT. An observation was also made of the domain state for saturation isothermal remanent magnetization (IRMs). The number and maximum size of grains which remain in a metastable single domain (SD) state increases with increasing field. This in turn gives rise to a field dependence of the total moment carried by such particles in the ensemble. By observing the number of metastable SD grains and estimating their volume one can construct a TRM induction curve. This curve approximates the known TRM induction curve for fine particles, demonstrating that the magnitude of TRM in fine particles of titanomagnetites is controlled by nucleation. This nucleation model also explains why weak field TRM is more stable against alternating field (AF) demagnetization than IRMs.
The demagnetization temperature necessary to remove viscous remanent magnetization
Authors: Enkin Randolph J. , Dunlop David J.
Published: February 2008

Recent experimental studies have shown that the temperature necessary to demagnetize viscous remanent magnetization (VRM) in magnetite‐bearing rocks is significantly higher than predicted by standard Néel single‐domain theory. The Walton time‐temperature equation, which has been invoked by some to explain the enhanced thermal stability, actually relates intensities of VRMs acquired at different temperatures rather than describing the unblocking of a previously acquired VRM. We show that the low‐field approximation (LFA) used in all previous formulations, which predicts equal VRM acquisition and decay rates, is not valid for a magnetite assemblage in the earth's field. A medium‐field approximation (MFA) predicts significantly faster VRM acquisition, and therefore greater thermal stability in decay, for the larger particles in the assemblage. Conventional theory does apply to red‐bed acquisition/decay experiments, since the LFA is valid for hematite.
Cometary H2+ and solar wind He2+ dynamics across the Halley cometopause
Authors: Fuselier S. A. , Shelley E. G. , Balsiger H. , Geiss J. , Goldstein B. E. , Goldstein R. , Ip W. ‐H.
Published: February 2008

Two Mass/Charge (M/Q) ≈ 2 distributions were observed by the Giotto Ion Mass Spectrometer/High Energy Range Spectrometer (IMS/HERS) during the encounter with comet Halley. The first, present throughout the encounter, is identified as solar wind He2+. The second, detectable only within ∼6 × 105 km of the nucleus, is identified as H2+ (produced primarily by dissociation and ionization of cometary H2O). When these two distributions are separated, distinct differences in their dynamics are apparent, particularly in the density and velocity profiles near the “cometopause”.
Magnetic lineations on the flanks of the Marquesas Swell: Implications for the age of the seafloor
Authors: Kruse Sarah E.
Published: February 2008

Four magnetic anomaly profiles across the Marquesas swell were obtained on the Crossgrain expedition of the R/V Thomas Washington in April 1987. The data cover a poorly dated region of the Pacific between the Galapagos and Marquesas fracture zones. Magnetic lineations trending approximately 350° in the vicinity of the swell were identified as anomalies 20 through 29, differing from identifications proposed by previous workers. Our identifications imply that the seafloor beneath the Marquesas Islands formed at a half‐spreading rate of approximately 40‐45 mm/yr during Paleocene and early Eocene time (65 to 50 Ma). The offset across the Marquesas fracture zone apparently increased from approximately 700 to 850 km between the times of anomalies 21 and 13.
The dynamical regime of fluid flow at the core surface
Authors: Bloxham Jeremy
Published: February 2008

We present an alternative method for determining the fluid motion immediately beneath the core‐mantle boundary, based on solving the full nonlinear core motions problem. We use this method to examine three dynamical hypotheses about the flow: the steady motions hypothesis; the geostrophic hypothesis; and the toroidal flow hypothesis. We obtain better fits to the field with the toroidal flows than with geostrophic flows, casting considerable doubt on the validity of the geostrophic hypothesis. Additionally, we find some indication that failure of the frozen‐flux approximation, a concomitant assumption, may be a serious obstacle to obtaining reliable maps of the core fluid flow.
Lateral variations near the core‐mantle boundary
Authors: Garnero Edward , Helmberger Donald , Engen Gladys
Published: February 2008

Differential travel times between S and SKS (Ts‐sks), and SKKS and SKS (Tskks‐sks), along with amplitude behavior have been used to study lateral variations at the core‐mantle boundary. The data were recorded by the World Wide Seismographic Station Network (WWSSN) and the Canadian Seismograph Network (CSN) from source regions in South America and the Fiji‐Tonga area. A core‐mantle boundary region traversed by SKS and S beneath the mid‐Pacific from the Fiji‐Tonga area to North American stations shows the most anomalous behavior in Ts‐sks. SKS and S are anomalously separated by up to 8 seconds. In addition to Ts‐sks anomalies, SKS and SKKS are anomalously separated by 2 to 3 seconds. A model fitting Ts‐sks for this anomalous region requires one or more of the following: (1) up to 5% increase in the top 300 km of outer core velocity; (2) a large scale high Vs region (2% increase) in the lower mantle NE of Tonga; (3) lateral variations in D” shear wave velocities of up to 3%. However, (1) above predicts a decrease in Tskks‐sks, contradicting the observations. This suggests that (2) and (3) are more likely explanations in modeling this data set.
Remanent magnetism at Mars
Authors: Curtis S. A. , Ness N. F.
Published: February 2008

We show that a strong case can be made for an intrinsic magnetic field of dynamo origin for Mars earlier in its history. The typical equatorial magnetic field intensity would have been ∼ 0.01‐0.1 Gauss. The earlier dynamo activity is no longer extant, but a significant remanent magnetic field may exist. A highly non‐dipole magnetic field could result from the remanent magnetization of the surface. Remanent magnetization may thus play an important role in the Mars solar wind interactions in contrast to Venus with its surface temperatures above the Curie point. The anomalous characteristics of Mars’ solar wind interaction compared to that of Venus may be explicable on this basis.
Nitric acid and ammonia emissions from a mid‐latitude prescribed wetlands fire
Authors: LeBel P. J. , Cofer W. R. , Levine J. S. , Vay S. A. , Roberts P. D.
Published: February 2008

We have obtained the first simultaneous measurements of gaseous nitric acid (HNO3) and ammonia (NH3) in the smoke plume of a wetlands biomass burn. These measurements were made using tungsten oxide‐coated diffusion denuder tubes from a helicopter during a prescribed burn at the Merritt Island National Wildlife Refuge, located at the NASA John F. Kennedy Space Center, Florida, on November 9, 1987. The mean NH3 and HNO3 mixing ratios measured in the smoke plume were 19 ppbv and 14 ppbv, respectively, both significantly higher than background mixing ratios. Nitric acid correlated well with carbon dioxide (CO2) produced by the combustion. The mean CO2‐normalized emission ratio for HNO3 was found to be 1.2 × 10−4. Ammonia, however, did not correlate well with CO2 suggesting a more complex relationship between combustion and production/release of NH3.
Balloon borne Antarctic frost point measurements and their impact on polar stratospheric cloud theories
Authors: Rosen James M. , Hofmann D. J. , Carpenter J. R. , Harder J. W. , Oltmans S. J.
Published: February 2008

The first balloonborne frost point measurements over Antarctica were made during September and October 1987 as part of the NOZE II effort at McMurdo. The results indicate water vapor mixing ratios on the order of 2 ppmv in the 15 to 20 km region, which is somewhat smaller than observed at mid‐latitude. This suggests that models of the springtime Antarctic stratosphere should be based on approximately 2 ppmv water vapor. The observed water vapor mixing ratio would correspond to saturated conditions for what is thought to be the lowest stratospheric temperatures encountered over the Antarctic. Through the use of available lidar observations there appears to be significant evidence that some PSCs form at temperatures higher than the frost point (with respect to water) in the 15 to 20 km region, thus supporting the binary HNO3‐H2O theory of PSC composition. Clouds near 15 km and below appear to form in regions saturated with respect to water; therefore they are probably mostly water ice clouds, although they could contain relatively small amounts of other constituents. Photographic evidence suggests that the clouds forming above the frost point have an appearance quite different from the lower altitude iridescent, colored nacreous clouds.
The anomalous circulation in the southern hemisphere stratosphere during spring 1987
Authors: Randel William J.
Published: February 2008

The general circulation of the Southern Hemisphere stratosphere during 1987 is analyzed based on National Meteorological Center analyses, and contrasted to a climatological average constructed from the years 1980‐1986. The polar lower stratosphere in spring 1987 is substantially colder than the climatology, with zonal mean differences of order 16K near 50 mb in November. Substantially warmer temperatures (near 8K) are observed in these data in the polar upper stratosphere coincident with the lower level cooling. Associated with the strong cooling in the lower stratosphere is a delay in the spring final warming during 1987 of approximately 20 days (compared with climatology). Although the majority of the observed cooling probably results from the record low ozone levels observed during 1987, the observed planetary wave driving during 1987 is substantially below climatological levels, also contributing to a colder pole.
Origin of subsurface water at Cajon Pass, California
Authors: Kharaka Yousif K. , White Lloyd D. , Ambats Gil , White Art F.
Published: February 2008

Samples of water and associated gases were collected from the Cajon Pass well using downhole samplers, and from the pipe stands at the completion of drill stem tests. The fluids were recovered from fracture systems in granitic rocks from two test intervals located at 1,829 to 1,905 m and 1,829 to 2,115 m. The intervals were initially cleaned by circulating into the hole fresh water and water spiked with fluorescein. Results of δD and δ18O values of formation water from this well and groundwater wells in the area indicate a meteoric origin, but recharge areas probably had higher elevations than that of the well or the recharge occurred in Pleistocene time when the mean annual temperatures were 3 ‐ 6°C lower than at present. The large differences in the δD and δ18O values of formation water indicate isolation of water within relatively proximal fracture systems. The isotope values of formation water plot on the Global Meteoric Water Line implying little water‐rock interaction.
Fracture related reflectors in basement rock from vertical seismic profiling at Cajon Pass
Authors: Leary P. C. , Henyey T. L. , Li Y‐G.
Published: February 2008

Multi‐azimuth VSP data acquired between 500 and 2000 meters deep in crystalline rock penetrated by the Cajon Pass deep scientific borehole show several reflectors intersecting the hole. The reflectors correlate with VSP amplitude data, drilling and cutting logs, and various geophysical logs. Most appear to be related to fracture zones or lithologic transitions accompaanied by fracturing, mineral alteration and fluid circulation. Amplitude systematics from two azimuthally different offsets are consistent with the presence of a high angle fault in the neighborhood of the well.
Synthetic seismogram modeling of shear‐wave splitting in VSP data from the Geysers, California
Authors: Shearer Peter M.
Published: February 2008

A vertical seismic profile data set showing shear‐wave splitting from The Geysers, California, can be approximately fit with synthetic seismograms calculated with geometrical ray theory for anisotropic models of aligned cracks in the uppermost crust. Limited agreement between data and synthetics can be obtained if the cracks are constrained to be vertical, but a much better fit is possible if the cracks dip at an angle of 55 degrees.
Thermal cleaning of viscous magnetic moments
Authors: Williams Wyn , Walton Derek
Published: February 2008

We calculate the demagnetizing temperature necessary to remove viscous magnetic moments from assemblies of single domain magnetite grains. It is shown that this cleaning temperature may be the same as that predicted by Pullaiah et al [1975] depending on the fraction of the viscous remanence removed. Experimental data by Williams ]1986] are shown to be in good agreement with the numerical calculations.
H2 emissions from the outer planets
Authors: Yelle Roger V.
Published: February 2008

Calculations of the H2 electronic band spectrum produced by fluorescence scattering of solar radiation are presented and compared with observations of the ultraviolet spectrum of Jupiter. The calculations demonstrate that the observed spectra are consistent with the suggestion by Yelle et al. [1987] that the bright H2 day‐glow of the outer planets is due predominantly to fluorescence of solar radiation. The calculations also demonstrate that large differences between solar scattered and electron excited spectra are evident at high spectral resolution. This fact may be used to observationally determine the relative importance of the two excitation mechanisms.
Latitudinal survey of water vapor in the middle atmosphere using an airborne millimeter wave sensor
Authors: Peter R. , Künzi K. , Hartmann G. K.
Published: February 2008

An airborne millimeter‐wave sensor has been used to determine the vertical H2O profile over the altitude range of 20 ‐ 70 km by measuring the thermal emission of the rotational transition at 183.31 GHz. Measurements were made between 45° N and 75° N during several flights in December 1986. At mid‐latitudes they showed water vapor mixing ratios between 3.5 and 5 ppmv with a maximum at 50 km altitude. At high latitudes a decrease to values less than 2.5 ppmv in the lower mesosphere and a maximum at 30 km was found. The characteristic decrease at high latitudes in the lower mesosphere in winter corresponds well with recent model calculations and is assumed to be caused by strong downward directed transport of mesospheric air.
Measurement of nighttime stratospheric N2O5 from infrared emission spectra
Authors: Kunde V. G. , Brasunas J. C. , Maguire W. C. , Herman J. R. , Massie S. T. , Abbas M. M. , Herath L. W. , Shaffer W. A.
Published: February 2008

The mixing ratio profile of N2O5 has been inferred from high‐resolution emission spectra obtained with a balloon‐borne Fourier spectrometer (SIRIS). The observations were taken for the period from midnight to predawn on September 16, 1986 at 32° N latitude. The inferred volume mixing ratio from nighttime average spectra has a peak of ∼ 1.8 × 10−9 in the 32‐35 altitude range. The inferred mixing ratio is generally less than the theoretical predictions from a 1‐D model.
Lightning and precipitation history of a microburst‐producing storm
Authors: Goodman Steven J. , Buechler Dennis E. , Wright Patrick D. , Rust W. David
Published: February 2008

Quantitative measurements of the lightning and precipitation life‐cycle of a microburst‐producing storm are described. The storm produced 116 total flashes of which only 6 were discharges to ground. The initial discharge occurred during a period of vigorous vertical development, approximately 4‐6 min after small hail was first indicated by radar. The peak flash rate of 23 flashes min−1 occurred only 7‐8 min later, 4 min prior to microburst onset, in conjunction with the peak in storm mass, vertically integrated liquid water content, echo volume, and cloud height. An abrupt decrease in the total flash rates is associated with storm collapse and serves as a precursor to the arrival of the maximum microburst outflows at the surface. Ice‐phase precipitation is shown to be an important factor in both the formation of the strong downdraft and the electrification of the storm.
A 3‐D seismic modeling study of the Ladron Horst near Socorrro, New Mexico
Authors: Chaimov Thomas A.
Published: February 2008

Three‐dimensional seismic modeling demonstrates that the intragraben horst‐like feature imaged on COCORP's Socorro‐Abo Pass survey in the Albuquerque Basin, New Mexico likely corresponds to the northeast‐plunging continuation of the Ladron uplift. This accords with the original interpretation which was expounded with reservations that the feature might be a result of side reflections off a nearby exposed basement uplift. This domed feature on Socorro Line 1A, referred to hereafter as the Ladron horst, cannot be a consequence of side reflections from the nearby Ladron Mountains. Three‐dimensional modeling defines a minimum northeastern extent of the Ladron uplift in the subsurface, confirms some aspects of previous interpretations, and offers a new interpretation of the apparent western boundary of the horst. Second‐order discontinuities in the reflections off the horst are modeled as normal faults within the subsurface basement uplift.