bluuebunny/crossref_metadata_2025 huggingface dataset:
A direct measurement of shear fracture energy in rocks
Authors: Cox S. J. D. , Scholz C. H.
Published: February 2008

Shear fracture energy has been measured for a granite and a limestone using a torsional method. We monitor failure with periodic stiffness determinations and measure strain energy released by integrating the load‐displacement record. Values of strain energy release rate (G3C) obtained for zero normal stress lie in the range 10²–10³ Jm−2. These fall between the values of G1C from tensile experiments and of shear fracture energy measured under high normal stress in triaxial tests.
Shear‐velocity structure from regionalized surface‐wave dispersion in the basin and range
Authors: Taylor Steven R. , Patton Howard J.
Published: February 2008

Lateral variations of shear velocity structure in the western United States are studied using observations of Rayleigh‐ and Love‐wave phase velocity dispersion. We measured Rayleigh‐wave dispersion in the 6‐60 sec period range on over 80 paths using both single‐and two‐station methods. Love‐wave dispersion was also measured on about 50 paths. A pure‐path regionalization method employing a block‐province grid is used to determine lateral variations of dispersion in the Basin and Range and adjacent geologic regions. Structural inversions of the regionalized Rayleigh‐wave dispersion curves indicate significant lateral variations in the crust and upper mantle structure of the Basin and Range and transition areas. A pronounced low‐velocity zone in the upper mantle is found under the Eureka heat flow province in the central Basin and Range. The lithospheric thickness in this province is 45 km in contrast to the Great Basin model of Priestley and Brune (1978; ∼65 km). Regionalization of Love‐wave data, together with the Rayleigh‐wave results, suggest the existence of polarization anisotropy in many areas of the Basin and Range. If verified, anisotropy must be accounted for in phase velocity inversions for the structure of the Basin and Range.
Dayside variation in auroral conjugacy
Authors: Dickinson Dale F. , Mende Stephen B. , Evans David S.
Published: February 2008

Observations of charged particle precipitation measured near Frobisher Bay by the NOAA‐7 and ‐8 satellites were compared with simultaneous photographs of auroras made by an image‐intensified, all‐sky camera located at the South Pole Station (the nominal magnetic conjugate point). The results show that auroral phenomena have a high degree of correlation between the two locations and demonstrate the expected poleward migration of the location of the auroras within each individual hemisphere during the midday hours. In addition, a systematic variation in the location of auroral phenomena in one hemisphere relative to the other is observed during the course of the day. The northern aurora moves further poleward in the noon to afternoon (magnetic local time) than does its southern counterpart. In contrast, the morning hours before 0900 MLT, show the northern features closer to the equator than the southern features. The conjugate point to the south pole, in effect, displayed a shift of approximately eight degrees during the course of a day.
Measurements of NOY species and O3 at 82° N latitude
Authors: Bottenheim Jan. W. , Gallant Allan G. , Brice Kenneth A.
Published: February 2008

Measurements of NO2, HNO3, and PAN, as well as O3 were made in March 1985 at Alert, N.W.T., Canada. The observations show that PAN is by far the dominant NOy species at this Northern location at the onset of spring. Surface loss of HNO3 and possibly O3 seemed to occur over the snowy surface, but no loss of PAN was apparent. The observations are further evidence for the importance of PAN as a major carrier of the oxides of nitrogen in the clean troposphere. Although concurrently measured light hydrocarbons would appear to be sufficient for local formation of PAN, it is suggested that this did not take place but rather that long range transport from more southerly regions was responsible for the observed PAN levels.
Global sources of local precipitation as determined by the Nasa/Giss GCM
Authors: Koster R. , Jouzel J. , Suozzo R. , Russell G. , Broecker W. , Rind D. , Eagleson P.
Published: February 2008

The origin of water precipitating in different geographic regions is investigated with the NASA/GISS GCM. Water evaporating from various source regions is "tagged" and then followed as a tracer in four model simulations, one for each season. The contributions of source region evaporations to simulated rainfall at specific locations is tabulated. The results show that in the summer, water vapor for midlatitude and high latitude precipitation tends to be recycled locally, whereas low latitude continental precipitation is more dependent on oceanic moisture sources.
Coherent pressure fluctuations observed at two sites on the deep sea floor
Authors: Webb Spahr C.
Published: February 2008

Pressure fluctuations from two sites on the deep sea floor separated by a distance of 32 km were found to be partially coherent at frequencies between .001 Hz and .015 Hz. The pressure fluctuations in this range are caused by surface gravity waves which are of sufficiently long wavelength that significant coherence exists. No coherence is detected at lower frequencies because temperature fluctuations disturb the reference in the pressure gauge, while at higher frequencies the surface gravity wave induced pressure fluctuations are sharply attenuated through the ocean. The real part of the coherency as a function of frequency resembles a Jo Bessel function of argument kr (r is the distance between the sites and k is the magnitude of the wavenumber as determined by the surface gravity wave dispersion relation). The imaginary part of the complex coherency is smaller than the real part over most of the surface gravity wave band. The coherency is well modeled if the surface gravity wave field is assumed to be isotropic, but other models for the directional spectrum which require a very broad distribution in direction of propagation fit equally well. Narrow beam width models fit the data poorly.
Increase of ion kinetic temperature across a collisionless shock: I. A new mechanism
Authors: Lee L. C. , Wu C. S. , Hu X. W.
Published: February 2008

A simple but effective mechanism is proposed to account for the increase of ion kinetic temperature across an oblique or perpendicular shock. This mechanism is based on the nonadiabatic motion of the transmitted ions across the shock ramp, which can lead to an ion gyrophase‐bunching behind the shock.
Cometary pick‐up ions observed near Giacobini‐Zinner
Authors: Gloeckler G. , Hovestadt D. , Ipavich F. M. , Scholer M. , Klecker B. , Galvin A. B.
Published: February 2008

In‐situ measurements of the rest‐frame distribution functions of cometary pick‐up water‐group ions are used to derive the number and energy density of these ions as a function of distance from the Comet Giacobini‐Zinner. The observed density profiles are found to be the same in the inbound and outbound passes and their shape is consistent with predictions of a simple model of pick‐up ion production from neutrals of a given type which flow radially outward at ∼1 km/s and are lost at a rate λ. Comparing predictions of this model with the measured density profiles we find that λ = 2·10−6 sec−1 and that the production rate of water‐group cometary molecules is 2.6·1028/sec. The measured distribution functions of the pick‐up water‐group ions may be represented by a two‐segment power‐law with a break at an energy EB ∼20 keV, corresponding to a speed, VB = 438(E/M)1/2, of ∼ 500 km/s at distances greater than ∼105 km. The shapes of the distribution functions indicate that the interaction process of the solar wind with cometary ions is predominantly stochastic.
On the influx of small comets into the Earth's upper atmosphere II. Interpretation
Authors: Frank L. A. , Sigwarth J. B. , Craven J. D.
Published: February 2008

Large, transient decreases of atmospheric dayglow intensities at ultraviolet wavelengths, primarily the atomic oxygen emissions at 130.4 nm, are interpreted in terms of an influx of heretofore undetected comet‐like objects. The primary composition of these comet‐like objects is water snow or clathrate in the form of a fluffy aggregate. These small comets are covered with a dust mantle and the tensile stress at fracture is estimated to be ∼ 0.1 dyne/cm². The water molecules that form the absorbing blanket for ultraviolet emissions arrive at the top of the earth's atmosphere as a piston of gas with bulk speed ≲ 20 km/sec. The mass of each of these comet‐like objects is ∼ 108 gm, or ∼ 100 tons. The global influx rate is ∼ 20 comets per minute. The global mass accretion rate by the earth's atmosphere is ∼ 1012 kg/year, and sufficient to replace the atmospheric mass in ∼ 5 × 106 years. The earth and the other bodies in the solar system would be thus more strongly coupled to cometary matter than presently thought.
The accuracy of Nimbus 7 LIMS temperatures in the mesosphere
Authors: Remsberg Ellis E.
Published: February 2008

Zonal‐mean temperatures from the LIMS experiment are compared with a temperature "climatology" derived from 4 years of Rayleigh backscatter lidar measurements at 44 N and for the months of March, April, and May, when wave activity and, thus, atmospheric variability is very weak. The mean difference between the two data sets is less than 3.5 K between 37 and 64 km and is consistent with the theoretical estimates of accuracy reported for the LIMS data. The effects of longitudinal and year‐to‐year variations in this comparison were considered, but they do not change the conclusions significantly. These validation results extend the altitude range of accurate LIMS temperatures in the mesosphere some 10 km higher than previously reported. It also means that the LIMS ozone and NO2 retrievals in the lower mesosphere should be free of any major temperature bias error effects.
The effects of upper‐mantle lateral heterogeneities on postglacial rebound
Authors: Sabadini Roberto , Yuen David A. , Portney Mark
Published: February 2008

We have investigated the potentially important effects arising from lateral heterogeneities on postglacial uplifts. Time‐dependent solutions for Maxwell rheology with lateral variations in the upper mantle are obtained by finite‐element techniques in cylindrical geometry. The displacements in the central portion of the ice sheet are not at all influenced by these lateral variations, whereas the uplifts near the edge of the ice load are extremely sensitive to lateral heterogeneities in the upper mantle. For ice sheets characteristic of the Laurentide ice sheet, deformations around the peripheral bulge can still be affected by an asthenosphere as far as twenty‐five degrees away. The continental lithosphere under the former ice load would appear to be thicker with the presence of a neighboring asthenosphere. Recent estimates of the North American plate thickness would exceed 250 km under these circumstances.
Rapidly occurring short duration discharges in thunderstorms, as indicators of a lightning‐triggering mechanism
Authors: Mazur Vladislav
Published: February 2008

Unusual rapidly occurring and small‐scale discharges in a narrow (1‐2 km) region inside the most electrically active part of a thunderstorm, observed with a VHF‐band (2 m wavelength) radar in East Georgia, USSR, were relatively stationary on the radar display, and had a maximum rate of about 200 per minute, an average duration of 12.5 ms, an estimated radar cross section a fraction of a meter to a few meters square, and an estimated length of a few meters to tens of meters. Occurrence of quasi‐stable discharges coincided with period of the highest altitude of the 50 dBZ‐reflectivity core. It is proposed that the quasi‐stable discharges are long sparks produced by the natural lightning‐triggering mechanism inside the storm. This hypothesis appears to support observations on triggered lightning in the United States obtained with an instrumented aircraft and wire‐trailing rockets.
Tidal decomposition of zonal neutral and ion flows in the Earth's upper equatorial thermosphere
Authors: Herrero Federico A. , Mayr Hans G.
Published: February 2008

Evidence is presented for strong coupling between the diurnal components of zonal neutral winds and ion drifts, suggesting that the relative importance of the E‐ and F‐region dynamos be re‐evaluated. Measurements of zonal neutral winds in the equatorial region of the Earth's thermosphere at an average altitude of about 350 km show that the nighttime zonal winds are very similar to the zonal ion‐drifts. That similarity is examined here comparing the corresponding tidal components of the 24 hr variations of these two parameters. The amplitude spectrum of the neutral winds exhibits primary and secondary maxima at the diurnal and ter‐diurnal frequencies respectively, while the ion‐drift spectrum shows only the diurnal maximum. It is found that the similarity between neutral winds and ion‐drifts is strongest in the diurnal mode where the phases differ by less than one half (0.5) hour, the amplitude of the ion‐drift being between 70% and 80% that of the neutral wind, suggesting a first order relation between the two quantities. The largest difference is found in the steady component representing superrotation; under similar conditions of solar activity, the ions superrotate with a velocity of about 30 m/s and the neutrals with 10 m/s. For the ions, the steady component, the phase of the semidiurnal component and the amplitude of the ter‐diurnal component appear to be sensitive to solar activity and are responsible for the observed solar cycle variations in the times of eastward‐to‐westward reversals between 0400 and 0700 LT. The ion‐drift diurnal amplitude and phase are relatively insensitive to changes in solar activity.
Dispersive ducting of MHD waves in the plasma sheet: A source of Pi2 wave bursts
Authors: Edwin P. M. , Roberts B. , Hughes W. J.
Published: February 2008

Fast magnetoacoustic waves can be ducted by plasma inhomogeneities such as the plasma sheet. As this ducting is dispersive an impulsive source will give rise to a well‐defined, quasi‐periodic wave packet with timescales determined by the width of the inhomogeneity and characteristic speeds in the wave duct and surrounding medium. The duration of the wave packet depends upon the distance from the source. We argue that an impulsive source in the plasma sheet at substorm onset will produce a wave packet near earth with characteristics similar to pi2 wave bursts and put this idea forward as a mechanism for the generation of pi2 pulsations.
Gyroradius effects on the energetic ions in the tail lobes of comet P/Giacobini‐Zinner
Authors: Daly P. W. , Sanderson T. R. , Wenzel K.‐P. , Cowley S. W. H. , Hynds R. J. , Smith E. J.
Published: February 2008

During the ICE fly‐by of comet P/Giacobini‐Zinner, a depletion is seen in the energetic ion intensities (E > 65 keV for "water group" ions) extending to about 40 min on either side of the time of closest approach (UT 1102 on September 11, 1985). It is demonstrated that the physical size of this hole is a few ion gyroradii (∼1.5 × 104 km). Angular analysis of the ion distributions in this "gyroradius region" can distinguish those ions whose gyromotion is entirely in one comet lobe, from those that cross the current sheet into the other lobe. In the central tail within a few minutes of closest approach, the single‐lobe ions exhibit high intensities and little pitch angle dependence whereas the ions crossing the current sheet have lower intensities and are streaming along the magnetic field away from the comet. The derived density gradients are used to determine the orientation of the current sheet at closest approach, as 44° east of north.
Plate motion controls on back‐arc spreading
Authors: Fein Jeremy B. , Jurdy Donna M.
Published: February 2008

The motions of the subducting and the overriding plates influence the spatial and temporal distribution of back‐arc spreading. Cenozoic plate motions in hot spot‐fixed and no‐net‐rotation reference frames were studied with attention to correlations between changes in motion and episodes of back‐arc spreading in the Western Pacific. The results suggest that major back‐arc opening occurs when both the overriding plate retreats from the trench in an absolute sense and the subducting plate undergoes a significant speed‐up. Neither phenomenon alone is sufficient to initiate spreading. Three major plate velocity increases can be identified in the Cenozoic : 1) the Pacific plate 5‐9 Ma; 2) the Indian plate at 27 Ma; and 3) the Pacific plate at 43 Ma, due to its shift from northerly to more westerly motion. At the present time, the Indian and Philippine are the only overriding plates that are retreating from their Pacific trenches and back‐arc spreading occurs only on these two retreating plates. Although the Indian plate has been retreating for at least 25 Ma, back‐arc spreading began only following the Pacific plate speed‐up 5‐9 Ma. Earlier, during the Indian plate speed‐up, no overriding plates were retreating strongly and no back‐arc spreading episodes are preserved from this time. For the earliest Pacific plate shift at 43 Ma, the Eurasian plate was not advancing, thus creating the only favorable plate kinematic conditions in the Cenozoic for back‐arc basin formation in this region. It is unclear whether extension in the Japan Sea is a result of these conditions.
Crystal growth of MgSiO3 perovskite
Authors: Ito Eiji , Weidner Donald J.
Published: February 2008

Single crystal of the orthorhombic perovskite modification of MgSiO3 have been grown from a melt at 27 GPa and 1830°C. The starting material of orthoenstatite was sealed in a platinum capsule with water. Crystals of good quality up to 200 microns in size were obtained, which are promising for the structural refinement, Brillouin spectroscopy, and other measurements. Some crystals, however, exihibit twinning on the (110) plane.
Discovery of energetic molecular ions (NO+ and O2+) in the storm time ring current
Authors: Klecker B. , Möbius E. , Hovestadt D. , Scholer M. , Gloeckler G. , Ipavich F. M.
Published: February 2008

A few hours after the onset of a large geomagnetic storm on September 4, 1984, energetic molecular ions in the mass range 28‐32, predominantly NO+ and O2+, have been discovered in the outer ring current at L ∼ 7. The data have been obtained with the time‐of‐flight spectrometer SULEICA on the AMPTE/IRM spacecraft. We find at 160 keV/e a mean abundance ratio of the molecular ions relative to O+ ions of 0.031±0.004. During quiet times no molecular ions are observed, the 1 σ upper limit of the ratio derived by averaging over several quiet periods is 0.003. The observations demonstrate the injection of ionospheric plasma into the storm time ring current and the subsequent acceleration to energies of several hundred keV on a time scale of a few hours after the onset of the magnetic storm.
Comment on the Paper “On the Influx of Small Comets into the Earth's Upper Atmosphere II. Interpretation” by L. A. Frank, J. B. Sigwarth, and J. D. Craven
Authors: Rubincam David Parry
Published: February 2008

It is unlikely that the dust mantles of small comets (cometary mass ∼105 kg, earth impact rate ∼20 per minute) suppress the evaporation of gases into the solar wind. An order‐of‐magnitude argument based on comet sizes, densities, and meteoritic dust influx indicate a maximum thickness for the mantles of ∼200 µm. A much more reasonable estimate gives a thickness of ∼0.2 µm. The mantles must be considered too thin to prevent the enrichment of the solar wind by evaporation.
Basaltic fissure eruptions, plume heights, and atmospheric aerosols
Authors: Stothers Richard B. , Wolff John A. , Self Stephen , Rampino Michael R.
Published: February 2008

Convective plumes that rise above Hawaiian‐style fire fountains consist of volcanic gases, aerosols, fine ash, and entrained heated air. Plume theory has been applied to observational estimates of the rate of thermal energy release from large fire fountains. The theoretically predicted heights of maintained plumes agree very well with the heights found from actual observations. Predicted plume heights for both central‐vent (point‐source) and fissure (line‐source) eruptions indicate a stratospheric penetration by plumes that form over vents with very high magma‐production rates. Flood basalt fissure eruptions that produce individual lava flows with volumes > 100 km³ at very high mass eruption rates are capable of injecting large quantities of sulfate aerosols into the lower stratosphere, with potentially drastic short‐term atmospheric consequences, like acid precipitation, darkening of the sky, and climatic cooling.
Magnetic connection for Saturn's rings and atmosphere
Authors: Connerney J. E. P.
Published: February 2008

Latitudinal variations in images of Saturn’s disk, upper atmospheric temperatures, and ionospheric electron densities are found in magnetic conjugacy with features in Saturn’s ring plane. We propose that these latitudinal variations are the result of a variable influx of water, transported along magnetic field lines from sources in Saturn’s ring plane. These features are thus the surface expression of an electromagnetic erosion mechanism which transports water (in the form of high charge‐to‐mass ratio particles) from the rings to the atmosphere.
Harmonically structured ULF pulsations observed by the AMPTE CCE Magnetic Field Experiment
Authors: Engebretson M. J. , Zanetti L. J. , Potemra T. A. , Acuna M. H.
Published: February 2008

Spectrograms of ULF waves in the 0 to 80 mHz frequency range have been prepared from magnetic field data obtained by the elliptically orbiting AMPTE/CCE satellite (with an apogee of approximately 8.8 Re. The most prominent feature of these spectrograms (which cover a full 15.6 hour orbit) is the presence of harmonically structured, azimuthally polarized pulsations in the outer magnetosphere during daytime hours. The frequencies of these pulsations decrease with increasing radial distance from the earth, indicating that they represent independent resonances of local magnetic flux tubes. The latitudinal structure of these harmonic pulsations, observed as AMPTE/CCE traveled to ± 16° magnetic latitude, is consistent with accepted field line resonance models. Correlations with IMP 8 satellite data confirm a close connection between appearance of these harmonic pulsations in the dayside magnetosphere and interplanetary magnetic field conditions favorable for the generation of upstream waves. Although we also observe pulsations associated with ring current injections, the monochromatic pulsations predicted by some theoretical models are extremely rare in the dayside AMPTE/CCE data set.
Snow melt and surface albedo in the Arctic Basin
Authors: Robinson David A. , Scharfen Greg , Serreze Mark C. , Kukla George , Barry Roger G.
Published: February 2008

Meteorological satellite imagery has been used to map the changes of surface brightness and texture associated with the seasonal progression of snow melt on the arctic pack ice in 1977 and 1979, and, using an image processor, surface albedo has been estimated. This is the first basin‐wide information on the temporal and spatial change of the ice surface and its albedo. In both years studied, melt progressed poleward from the Barents and Kara Seas and from the southern Beaufort and Chukchi Seas. Average surface albedo of the Arctic Basin fell to 0.40, and in the central Arctic to about 0.50, in late July of each year, but the melt occurred approximately 3 weeks later in 1979 than in 1977. Results suggest a significant year‐to‐year variability in the arctic energy and mass balances.
Comment [“ On the influx of small comets into the Earth's upper atmosphere I. Observations”]
Authors: Hanson W. B.
Published: February 2008

A search of ion concentration data from the AE‐E, AE‐C, and DE‐2 spacecraft was made to look for evidence of the small‐comet influx into the upper atmosphere that has been suggested by Frank, Sigwarth and Craven (1986a). No simple signature of these events was discovered, though many events should have been encountered in the data examined. Either the cometary flux is more than an order of magnitude less than proposed, or else the ionospheric signature is more subtle than assumed here.
A seismically active section of the Southwest Indian Ridge
Authors: Wald David J. , Wallace Terry C.
Published: February 2008

The section of the Southwest Indian Ocean Ridge west of the Prince Edward Fracture zone has a large ridge axis offset and a complicated ridge‐transform morphology. We have determined the source mechanisms of transform earthquakes along this portion of the ridge from an inversion of long‐period P and SH waveforms. The seismicity is characterized by anomalous faulting mechanisms, source complexity and an unexpectedly large seismic moment release. Several earthquakes with dip‐slip components of faulting have been recognized on the central section of the Andrew Bain and 32° E transforms suggesting geometrical complexity along the transform. This region has experienced a Mw = 8.0 transform earthquake in 1942, yet we observe a seismic slip rate during the last 20 years that is still comparable to the predicted spreading rate (1.6 cm/yr). The calculated slip rate over a period of 60 years is three times greater than the expected rate of spreading.
On the cooling of stratospheric temperature at Syowa, Antarctica
Authors: Chubachi Shigeru
Published: February 2008

Strong cooling is observed from 1974 to 1985 of the 100 mb temperature in November at Syowa (69°S, 40°E). Similar cooling is also seen in other pressure levels (70, 50, and 30mb levels) and other months. The rate of change for each month is very similar to the one of total amount of ozone at Syowa. A simple model is proposed which link ozone and temperature decrease at Antarctica.
Polar stratospheric clouds inferred from satellite data
Authors: Austin J. , Remsberg E. E. , Jones R. L. , Tuck A. F.
Published: February 2008

Anomalously high radiances from the ozone channel of the Limb Infra‐red Monitor of the Statosphere (LIMS) sounding instrument have been observed in the Northern Hemisphere winter lower stratosphere. Such events, thought to be due to polar stratospheric clouds (PSCs) are examined further by computing relative humidities using Stratospheric Sounding Unit (SSU) temperatures and water vapour measurements from the LIMS Map Archive Tape (MAT) analyses. Regions identified as PSCs are found to correspond closely to regions of high humidity. While instances of saturation were found, the average humidity at the centres of 39 PSCs was calculated to be 58%. Possible reasons for this apparent discrepancy are discussed.

Applying a similar approach to the Southern Hemisphere, in 1979, virtually no PSCs are found in the vortex after 10 September at 20 km. This result has important implications for a number of proposed explanations for the Antarctic ozone hole.
Sam II measurements of Antarctic PSC's and aerosols
Authors: McCormick M. P. , Trepte C. R.
Published: February 2008

Measurements by the SAM II satellite instrument show that polar stratospheric clouds (PSC's) are a regular feature of the austral winter season in either nonvolcanically or volcanically disturbed periods. The tops of these clouds are observed above 20 km in early winter and descend in altitude over the course of the season to heights near 15 km in mid September. Typically, PSC's persist in the lowest stratospheric altitudes throughout September. Subsequently, October always represents a relative annual minimum in aerosol extinction above 15 km and in stratospheric column amount. In addition, volcanically produced aerosols in Antarctica peaked in early 1983 and, if linearly related to ozone losses, are probably not a contributing factor to the continued loss of total ozone in the Antarctic spring in 1984 and 1985.
Wave propagation effects and the Earth's structure in the lower mantle
Authors: Haddon R. A. W. , Buchbinder G. G. R.
Published: February 2008

Lay and Helmberger and their co‐workers have recently proposed models of Earth structure in which the S‐velocity increases discontinuously with depth by about 3% at the bottom of a postulated region of abnormally low (near zero) gradient between depths of about 2300 and 2600 km in the lower mantle. Such models involve drastic departures from previously proposed models of Earth structure in this region. By use of Kirchhoff wave theory it is shown that the pertinent data may be interpreted alternatively as an effect of wave propagation in an inhomogeneous lower mantle. On this alternative interpretation the S‐velocity need nowhere sharply increase with increasing depth at any level in the lower mantle.
Interaction of mantle dregs with convection: Lateral heterogeneity at the core‐mantle boundary
Authors: Davies Geoffrey F. , Gurnis Michael
Published: February 2008

Preliminary numerical models indicate that chemically denser material (dregs) at the base of the mantle would have substantial lateral variations in thickness induced by convection of the overlying mantle, and might well form discontinuous aggregations below mantle upwellings. A model with a density contrast of about 2 per cent and an initial uniform thickness of the denser layer of 100 km yields a discontinuous distribution with maximum thickness 230 km and bottom topography of several kilometers amplitude, in reasonable accord with recent seismological observations of vertical and lateral structure. Heat flux out of the core is probably strongly modulated laterally by mantle convection, while mantle dregs will complicate and possibly amplify this effect. Such modulation may be relevant to long‐term (107 ‐ 108 year) variations in the magnetic field.
Depletion of Antarctic ozone: Height of ozone loss region and its temporal changes
Authors: Iwasaka Y. , Kondoh K.
Published: February 2008

Ozonesonde measurements at Syowa Station (69°00′S, 39°35′E) from 1971 to 1984 show that ozone depletion is most striking in the region 10km to 25km in the last five years. Active ozone loss region in the spring shows good correspondence to the region where noticeable drop in stratospheric temperature is observed from 1981 to 1985, but only in the spring.

Monthly averaged lower‐stratospheric temperature decreased smoothly during the period from about 1975 to the present in the spring. The temperatures in October and November of 1985 are comparable to the frost point temperature of water vapor with 10 ppmv mixing ratio at about 100mb. The temperature drops observed in interannual trends could activate formation of ice particles, and cause noticeable ozone loss in spring through heterogenous ozone reduction reactions.
Grain‐scale deformation and the fold test ‐ evaluation of syn‐folding remagnetization
Authors: van der Pluijm Ben A.
Published: February 2008

The paleomagnetic fold test examines for pre‐, syn‐ or post‐folding (re)magnetization. Generally, passive limb rotation is used to restore folded units to their original position, and the position of the Fisherian maximum determines the relationship between folding and magnetization. In a more complete analysis, the reorientation of material lines in different fold models is used. However, the magnetic vector should not be considered a material line as it represents the sum of vectors in individual magnetic carriers and does not cross grain boundaries. Therefore, the role of grain‐scale deformation mechanisms was examined, using two end members: rigid‐body rotation (spin) and homogeneous strain.

From this study it is concluded that (1) the Fisherian maximum will in general occur before complete unfolding, (2) the sign of the inclination may change during unfolding and, consequently, ’cross‐over’ unfolding is not representative of syn‐folding remagnetization, (3) statistical analysis will not necessarily produce significant results. A number of recommendations are given, which include: stepwise unfolding (and unplunging) should be carried out routinely; local, rather than regional, fold tests should be performed; both limbs and the hinge of a single folded layer should be examined in order to determine the active deformation mechanisms that will enable corrections to be carried out; in addition to Fisherian statistics, the angle between magnetic vector and bedding across a fold should be measured and used for correction.
Latitudinal and radial gradients of anomalous and galactic cosmic rays in the outer heliosphere
Authors: Cummings A. C. , Stone E. C. , Webber W. R.
Published: February 2008

We have used measurements from instruments on Voyagers 1 and 2 and Pioneer 10 to derive simultaneous radial and latitudinal gradients of anomalous cosmic‐ray oxygen during the latter part of 1985. We find that in the energy interval from 7.1‐30.6 MeV/nucleon the latitudinal gradient is −3 to −4%/deg. The sign of the latitudinal gradient is opposite to that reported for the last solar cycle when the solar magnetic field polarity was reversed, as predicted by propagation models in which curvature and gradient drifts are significant. The ratios of the radial and latitudinal gradients of anomalous oxygen, anomalous helium, and galactic cosmic rays are similar, also in agreement with drift theory predictions. Based on drift theory, these observed ratios, which are near unity, lead to estimates of κ⟂/β in the range of 3‐8 × 1022 cm²/sec at 24.9 AU for particles with rigidities of ∼2‐3 GV.
The vertical distribution of radiogenic heat production in the Precambrian crust of Norway and Sweden: Geothermal implications
Authors: Pinet Christophe , Jaupart Claude
Published: February 2008

The present geology of southern Scandinavia offers the unique opportunity to sample deep and intermediate levels from the same crustal section for both heat flow and heat production. In the central part of southern Norway, amphibolite facies terranes appear to lie on top of the same deeper crustal formations which crop out on their western and eastern margins. An extensive data set on the geochemistry of all types of rocks in the region culled from the literature is used to derive values for radiogenic heat production for each kind of crustal facies. Using constraints from heat flow data in the same area allows a reliable model of the distribution of crustal heat production. The average heat production of granulite facies terranes is 0.4 µW/m³, similar to values in other parts of the world. For amphibolite facies rocks, the value is 1.6 µW/m³. The present shield also includes heat producing element enriched granites formed in later events and the average heat production of presently exposed crust is 2.7 µ/m³. Using heat flow and radioactivity data from ten stations, the reduced heat flow in the area is 22 ± 2 mW/m². This corresponds to the heat flow at the top of 28 km of deep crustal facies, implying that the mantle heat flow is probably as low as 10 mW/m². Over the whole crustal thickness, the average amount of radiogenic heat is 31 mW/m².
Redbeds and thermoviscous magnetization theory
Authors: Kent Dennis V. , Miller John D.
Published: February 2008

Thermal demagnetization characteristics of a Brunhes‐age viscous overprint in Appalachian redbeds and a thermoviscous component acquired in the laboratory at moderate temperature agree well with relaxation time‐blocking temperature relations for hematite proposed by Pullaiah et al. [1975]. Supporting evidence was obtained from redbeds associated with an igneous dike intrusion although the interpretation of these data are complicated by magnetochemical alterations. Paradoxically, experimental data for magnetite in some limestones were shown to agree more closely with an alternative theory of Walton [1980]. The hematite in redbeds is predominantly singledomain (SD) whereas magnetite in the limestones studied extends well into the multidomain (MD) range. Thus experiment and theory could be reconciled if it is assumed that Pullaiah et al. applies strictly to SD material whereas Walton's theory somehow describes thermoviscous effects dominated by larger MD grains.
Majorite partition behavior and petrogenesis of the Earth's upper mantle
Authors: Kato Takumi , Irifune Tetsuo , Ringwood A. E.
Published: February 2008

The partitioning of La, Sm, Yb, Sc and major elements between majorite garnet and ultrabasic liquid has been studied experimentally at 16 GPa and 2000°C. Liquidus majorite possesses a Si/Mg ratio of 1.05 as compared to the Cl chondritic ratio of 0.95, so that extraction of more than 50% of majorite from a chondritic mantle composition would be required to obtain the pyrolite Si/Mg ratio of 0.78 in the upper mantle. Liquidus majorite is enriched in Al, Sc and Yb compared to the melt by almost a factor of two and is similarly depleted in Ca, Sm and Ti. Thus extensive majorite fractionation would necessarily imprint non‐chondritic Sm/Yb, Sm/Sc, Al/Ca and Al/Ti ratios on the coexisting liquid. These partition relationships demonstrate that the present upper mantle, which possesses these elements approximately in chondritic relative abundances, cannot have experienced prior separation of more than about 10% of a majorite garnet phase.
Energetic neutral atom image of a storm‐time ring current
Authors: Roelof Edmond C.
Published: February 2008

An image formed in 5 minutes by energetic neutal atoms (ENA) emitted by charge exchange with ring‐current energetic ions (∼ 50 keV) has been constructed and analyzed from ISEE 1 measurements at a radial distance of 2.6 Re during the main phase (Dst = −241 nT) of the geomagnetic storm of September 29, 1978. Comparison with simulated images calculated from a simple model of the global ring‐current ion distribution implies a strong (≳ 20:1) midnight/noon ion intensity asymmetry. Estimated ion fluxes in the midnight meridian (3.0 < r < 5.0 Re) are 2.5 × 106 (cm² s sr keV) −1 for 30 keV H+ (if H‐atoms dominated the ISEE 1 ENA fluxes) or 1.0 × 106 (cm² s sr keV)−1 for 70 keV O+ (if O‐atoms dominated). ENA fluxes (whether H or O) from the brightest areas of the image exceed 10³ (cm² s sr keV)−1.
The solar wind‐magnetosphere‐ionosphere current‐voltage relationship
Authors: Fedder J. A. , Lyon J. G.
Published: February 2008

The nature of the solar wind‐magnetosphere‐ionosphere (SW‐M‐I) coupling has been a subject of intense study and scientific interest. We report results from a numerical simulation of the SW‐M‐I system which shed light on the physics and behavior of the controlling processes. The current‐voltage relationship is characteristic of a magnetohydrodynamic dynamo with a load operating near short circuit conditions. We discuss the operation of the dynamo, its location with respect to the magnetosphere, and important implications of the results for both the earth and other planets with intrinsic magnetic fields.
Asymmetry of the heliosphere
Authors: Suess S. T. , Hathaway D. H. , Dessler A. J.
Published: February 2008

The outflowing solar wind interacts with the local interstellar medium to form the heliospheric cavity within which the solar wind is supersonic. Because the interstellar medium is moving with respect to the Sun, and because the solar wind has a latitude dependence, the heliosphere is asymmetric. The flow of the interstellar medium past the heliosphere produces an asymmetry because of the Bernoulli effect, which draws the heliosphere out in a direction orthogonal to the upstream‐downstream axis, and because of a viscous interaction, which draws out the heliosphere downstream. We consider a variety of cases and find the effects to be significant with, typically, the upstream direction having a heliospheric dimension that is 2/3 the downstream dimension. Suggestions have been put forth to the effect that a spacecraft penetration of the heliospheric shock wave may be imminent. Because one of the most distant spacecraft is moving roughly in the upstream direction relative to the interstellar flow, and the other is moving in the downstream direction, the distance to their encounters with the heliospheric shock may differ by as much as 40 AU.
Seasonal variations of sea ice motion in the Canada Basin and their implications
Authors: McLaren A. S. , Serreze M. C. , Barry R. G.
Published: February 2008

Ice velocities and sea level pressure data from Arctic drifting buoys for 1979‐85 are used to examine the seasonal variation of sea ice drift in the Canada Basin. A recurring reversal of the mean anticyclonic gyre is demonstrated in late summer, in response to changes in atmospheric forcing. The identification of this reversal of ice motion is significant for numerical modeling of Arctic atmosphere‐ocean‐ice interactions.
Charge exchange avalanche at the cometopause
Authors: Gombosi Tamas I.
Published: February 2008

A sharp (≤104 km thick) transition from a solar wind proton dominated flow to a plasma population primarily consisting of relatively cold cometary heavy ions has been observed at a cometocentric distance of about 1.6×105 km by the VEGA and GIOTTO missions. This boundary (the cometopause) was thought to be related to charge transfer processes, but its location and thickness are inconsistent with conventionally estimated ion ‐ neutral coupling boundaries. In this paper a two‐fluid model is used to investigate the major physical processes at the cometopause. By adopting observed comet Halley parameters the model is able to reproduce the location and the thickness of this charge exchange boundary.
The upper mantle degree two pattern: Constraints from geoscope fundamental spheroidal mode eigenfrequency and attenuation measurements
Authors: Romanowicz Barbara , Roult Genevieve , Kohl Thomas
Published: February 2008

We have analyzed fundamental spheroidal mode spectra obtained from very long period Geoscope records, in terms of global distribution of eigenfrequencies and attenuation. With a new data set and a different data processing approach, involving time variable filtering and the removal of higher order effects in the spectra, we confirm the strong upper mantle degree two signature in the eigenfrequency data. The higher frequency content of the Geoscope spectra allows us to put better constraints on the depth range at which this pattern originates, which appears to be somewhat shallower than was proposed before. While some effect may persist down to the bottom of the transition zone, the frequency signature of the strongest degree two pattern requires an S velocity heterogeneity concentrated in the depth range 300‐500 km and this signature is also apparent in the distribution of Q, which is indicative of a probable thermal origin. The data also resolve a shallow degree 2 pattern, well explained by heterogeneity spanning from the surface to depths of about 300 km, and associated with the distribution of tectonic provinces. It is shifted by about 45° with respect to the deep degree 2 pattern, and its expression in the Q data is not clear.
Laboratory studies of sticking coefficients and heterogeneous reactions important in the Antarctic stratosphere
Authors: Leu Ming‐Taun
Published: February 2008

Laboratory studies of sticking coefficients of H2O, HCl, Cl2 and HNO3 on ice and heterogeneous reactions of ClONO2 with ice or HCl/ice have been performed in a fast flow reactor. A quadrupole mass spectrometer with electron impact ionization was used as a detector. Measured sticking coefficients are: 0.3 (+0.7. −0.1) for H2O, 0.4 (+0.6, −0.2) for HCl, <1.0 × 10−4 for Cl2, and 0.3 (+0.7, −0.1) for HNO3 at 200 K. The reaction probability of ClONO2 on ice was found to be 0.06 (±0.03) while HOCl was observed as a sole product in the gas phase. With HCl present in ice, the reaction probability of ClONO2 is greatly enhanced, approaching 0.27 (+0.73, −0.13) while molecular chlorine was found to be the major product in the gas phase. Another reaction product was nitric acid which remained in the solid phase. Since the polar stratospheric clouds contain ice particles or possibly HCl/ice particles on the surface, the present results should be a major factor in producing the observed springtime ozone depletion in the Antarctic stratosphere.
Aerosol size‐temperature relationship
Authors: Shaw Glenn E.
Published: February 2008

It has been discovered that the size distribution of atmospheric aerosols in air masses over central Alaska varies systematically with air temperature. Cold air masses contain relatively few, coarse aerosols. Aerosols in warm Pacific‐marine air masses, on the other hand, are plentiful in number, but their mean size and mass loading is small. There are decreasing numbers of cloud condensation nuclei, but substantial increases in aerosol mass with decreasing temperatures. We speculate that the cause is related to a combination of air pollution transport from Eurasia into the Arctic air mass and photolytic creation of nuclei in the sunlit Northern Pacific.
Lightning‐associated precipitation of MeV electrons from the inner radiation belt
Authors: Inan U. S. , Burgess W. C. , Wolf T. G. , Shater D. C. , Orville R. E.
Published: February 2008

Transient perturbations of subionospheric very low frequency (VLF) radiowave signals provide new evidence for lightning‐induced electron precipitation (LEP) events involving short (<1 s) bursts of >1 MeV electrons from the earth's inner radiation belt at L ≤1.8. The signal amplitude changes are attributed to increased absorption in the earth‐ionosphere waveguide and/or alterations of the waveguide mode structure due to localized secondary ionization enhancements produced in the nighttime lower ionosphere and the mesosphere by the precipitating electrons. The otherwise stably trapped electrons are believed to be scattered in pitch angle during cyclotron resonant interactions in the magnetosphere with the lightning‐generated whistler waves. That some precipitation bursts consist partly of MeV electrons is suggested by (i) confinement of the perturbed subionospheric signal path to low magnetic latitudes (L ≤1.8), for which corresponding electron energies for gyroresonance with typical whistler‐wave frequencies in the magnetosphere are >1 MeV, and (ii) the temporal signatures of the perturbation events, which often exhibit an unusually rapid initial recovery (time constant of τ <1 s) followed by further recovery at rates believed characteristic of less energetic events (τ ∼5–20 s). The latter is interpreted as a manifestation of the rapid variation with altitude of the effective loss rate for excess ionization over an exceptionally wide range of mesospheric altitudes (40–70 km) penetrated by the >1 MeV electrons.
Note on temperature dependence of exchange constant in magnetite
Authors: Heider Franz , Williams Wyn
Published: February 2008

We calculated the temperature dependence of the exchange constant between 20°C and 573°C using three previously published data sets from inelastic neutron scattering by spin wave excitations in magnetite. The exchange constant in magnetite varies as a function of temperature approximately as the saturation magnetization to the power 1.7. Our synthesis of temperature dependent spin wave dispersion data provides an experimental foundation for the temperature variation of the exchange energy which is critical for micromagnetic domain structure calculations and for an understanding of the acquisition of thermoremanent magnetization in rocks.
Variation of depth to the brittle‐ductile transition due to cooling of a midcrustal intrusion
Authors: Gettings M. E.
Published: February 2008

The depth to the brittle‐ductile transition in the crust is often defined by the intersection of a shear resistance relation in the brittle upper crust that increases linearly with depth and a power law relation for ductile flow in the lower crust that depends strongly on temperature. Transient variation of this depth caused by a magmatic intrusion at a depth near the regional transition can be modeled by a heat conduction model for a rectangular parallelepiped superimposed on a linear geothermal gradient. When parameters appropriate for the southeastern United States are used, a moderate‐sized intrusion is found to decrease the transition depth by as much as 7 km; significant variations last about 10 m.y. Since the base of the seismogenic zone is identified with the brittle‐ductile transition and since significant depth variations provide loci for strain energy concentration, these results imply that intrusions of late Tertiary age or younger could be important sources of clustered seismicity.