bluuebunny/crossref_metadata_2025 huggingface dataset:
Revised paleomagnetic pole for the Sonoma volcanics, California
Authors: Mankinen Edward A.
Published: February 2008

Paleomagnetic sampling of the Miocene and Pliocene Sonoma Volcanics, northern California, was undertaken to supplement an earlier collection. Data from 25 cooling units yield positive fold and reversal tests, and a paleomagnetic pole located at 80.2°N., 069.2°E., with α95 = 6.8°. This paleopole is significantly displaced (9.6° ± 5.3° of latitude) to the farside of the geographic pole. A highly elliptical distribution of the data in both direction and VGP space indicates that incomplete averaging of geomagnetic secular variation is a more likely explanation for this anomaly than is northward translation of the volcanic field.
Evidence for a remanent contribution in Magsat data from the Cretaceous quiet zone in the south Atlantic
Authors: Fullerton Lawrence G. , Frey Herbert V. , Roark James H. , Thomas Herman H.
Published: February 2008

Indirect evidence for the presence of a TRM component in the MAGSAT elevation data in the South Atlantic is found through forward modeling of the prominent positive anomaly overlying the Walvis Ridge. The anomaly contrast between the Ridge and adjacent Angola and Cape Basins is too large to be easily explained by induced magnetization of even alkali basaltic crust. However, most of the Walvis Ridge and portions of the adjacent basins lie within the Cretaceous Quiet Zone where prolonged normal polarity may have produced enough volume of material to cause a measureable contribution at satellite elevation. An additional 3 A/m (spread over the entire layer 2 thickness) TRM contribution is required to account for the Walvis Ridge anomaly. This value is within the range found for the Cretaceous Quiet Zone anomalies in the MAGSAT data in the North Atlantic.
Fast Fermi acceleration in the plasma sheet boundary layer
Authors: Wu C. S. , Lui A. T. Y. , Mandt M. E. , Krauss‐Varban D.
Published: February 2008

A longstanding question in the field of magnetospheric physics is the source of the energetic particles which are commonly observed along the plasma sheet boundary layer (PSBL). Several models have been suggested for the acceleration of these particles. We suggest a means by which the fast Fermi acceleration mechanism [Wu, 1984] can accelerate electrons at the plasma sheet and perhaps account for some of the observations. We propose the following: A localized hydromagnetic disturbance propagating through the tail lobe region impinges upon the PSBL deforming it and displacing it in towards the central plasma sheet. The boundary layer can then act like a moving magnetic mirror. If the disturbance is propagating nearly perpendicular to the layer then its velocity projected parallel to the layer (and the magnetic field) can be very large resulting in significant acceleration of reflected particles.
Evidence of significant nonrandom behavior in the recurrence of strong El Niño between 1525 and 1988
Authors: Hanson Kirby , Brier Glenn W. , Maul George A.
Published: February 2008

The precise character of the quasi‐periodic variation in the recurrence of El Niño events has been unclear. To gain insight into the nature of this apparent regularity, a 464‐year record (1525‐1988) of the initiation of "strong" El Niño events, derived from the chronology of Quinn et al. [1987], has been analyzed with a two‐dimensional extension of the periodogram analysis method of Buys Ballot. The method is useful for detecting joint nonlinear interactions between variations at two specified periods. Results indicate joint nonrandom recurrence of strong El Niño events at periods of 6.75 and 14.0 years. From Monte Carlo tests, we estimate the statistical significance of this result to be at the 0.1% level. Alternating ∼95 year‐long time‐blocks, where 6.75‐year and 14.0‐year recurrence periods dominate, is apparent from the analysis. No specific mechanism is offered for the periodic forcing of strong El Niño events, but our observation of significant quasi‐periodic behavior in the initiation of such events at the combined periods of 6.75 and 14.0 years may be a useful clue in efforts to understand and model natural ENSO recurrence.
Dynamics of Pluto and Charon
Authors: Dobrovolskis Anthony R.
Published: February 2008

The dynamics of the Pluto‐Charon system are reviewed from a historical perspective. Although Pluto‧s orbit crosses Neptune‧s, an intricate system of nested resonances keeps these planets apart. Pluto‧s orbit is apparently chaotic as well. Pluto always keeps the same face turned toward Charon, and vice versa. Tides also damp Charon‧s orbital eccentricity and inclination. Precession of Pluto‧s orbital plane causes Pluto‧s obliquity to vary periodically from formally prograde to retrograde. Pluto is probably an original member of the Solar system, but not an escaped satellite of Neptune. The Voyager II encounter with Neptune, the final Pluto‐Charon mutual events, and the next generation of telescopes are bound to reveal some surprises.
Impact jetting of water ice, with application to the accretion of icy planetesimals and Pluto
Authors: McKinnon William B.
Published: February 2008

Jetting can occur during oblique impacts of water ice bodies at relative velocities as low as ∼500 m s−1, because of the low Hugoniot elastic limit and high compressibility of ice compared to rock. In jetted ice, incipient melting, complete melting, and incipient vaporization occur, upon release to low pressure, at impact velocities of 1.3, 2.0, and 2.7 km s−1, respectively, much less than the 3.4, 4.4, and 5.3 km s−1, required in head‐on collisions. Uncertainties in the shock equation‐of‐state may allow complete melting during jetting at relative velocities as low as 1.2 km −1. Because jet speeds exceed impact speeds, often by a factor of several, during the accretion of icy bodies greater than a few 100 km in radius there may be a significant loss of icy material. This is more true if the accreting body is large enough to differentiate so that its surface layers are closer to pure ice in composition, and especially true if bodies of comparable size are involved, which emphasizes the obliqueness of the collision. I suggest that it is jetting during a Charon‐forming collision (and not vaporization) that may account for Pluto‐Charon's relatively large rock/ice ratio, should the C/O ratio of the solar nebula turn out to be too low to sufficiently raise the rock/ice ratio of outer solar nebula condensates by formation of non‐condensable CO.
Crater relaxation on Ganymede: Implications for ice rheology
Authors: Hillgren Valerie J. , Melosh H. J.
Published: February 2008

Controversy has existed over whether or not viscous relaxation is an important process on the icy satellites. Previous models involved large extrapolations of Newtonian flow laws for ice, whereas ice is known to exhibit non‐Newtonian behavior. Recently, the flow law parameters for ice at the appropriate temperatures and stresses have been measured. Numerical modelling of the viscous relaxation of basins on Ganymede using these parameters has given implausibly short relaxation times. However, this model treated ice as a purely viscous substance, so that no elastic lithosphere could develop near the surface. Here we treat ice as a Maxwell visco‐elastic material and numerically model the relaxation of basins on Ganymede. We find that realistic Young's moduli lead to little relaxation occurring in basins even 4.0 Ga after their formation. Further, we demonstrate that within broad limits the near surface temperature gradient has little effect on this result. Finally, through examination of the distribution of Maxwell times in the vicinity of the crater, we show that most viscous relaxation occurs early in the basin's history when stresses are high, and thus Maxwell time is short. As stresses are relieved, the Maxwell time becomes long, and relaxation essentially ceases.
Tunable diode laser measurements of CH3OOH absorption cross‐sections near 1320 CM−1
Authors: Becker K. H. , Brockmann K. J. , Bechara J.
Published: February 2008

Infrared absorption spectra and absorption cross‐sections in the C‐H deformation band of CH3OOH near 1320 cm−1 have been measured with a tunable diode laser spectrometer. Methylhydroperoxide concentrations in a slowly flowing gas mixture were determined by UV absorption. Peak absorption cross‐sections of the strongest lines observed were found to lie in the range (0.5 –1.5) × 10−18 cm² under near Doppler‐limited conditions. The dependence of the peak absorption cross‐sections on total air pressure in the range 2.5–90 torr was also investigated, and the possibility of CH3OOH atmospheric mixing ratio measurement with a tunable diode laser assessed.
Inverse magnetic fabric in deformed limestones of the Morcles Nappe, Switzerland
Authors: Ihmlé P. F. , Hirt A. M. , Lowrie W. , Dietrich D.
Published: February 2008

Anisotropy of magnetic susceptibility (AMS) was measured at 15 sites in deformed Helvetic limestones of the Morcles nappe in western Switzerland. Inverse magnetic fabrics, characterized by axes of maximum susceptibility subperpendicular to bedding or cleavage, were observed at four sites in the root zone of the nappe. Acquisition and thermal demagnetization of isothermal remanent magnetization show that the ferromagnetic mineralogy is dominated by pyrrhotite, with various proportions of magnetite, hematite and goethite. The matrix minerals were studied in thin section with a staining technique to distinguish different carbonates, by X‐ray texture goniometry and by microprobe analysis. Observations of AMS at room and liquid nitrogen temperatures, and of the temperature dependence of bulk susceptibility, lead to the conclusion that the inverse fabrics result from a paramagnetic component due to Fe2+ ions in the calcite matrix.
Computer simulations of iron in magnesium silicate perovskite
Authors: Wright Kate , Price Geoffrey D.
Published: February 2008

We use atomistic computer simulation techniques to investigate the site partitioning of iron in (Mg,Fe)SiO3 perovskites. Our calculations predict that the most energetically favourable reaction for iron substitution will be a direct exchange of Fe2+ for Mg2+. Substitution of Fe into the octahedral site and Si into the 8–12 fold coordinated site, as proposed by Jackson et al. [1987], is predicted to be extremely unlikely.
A slow seismic event recorded in Pasadena
Authors: Kanamori Hiroo
Published: February 2008

A prominent long‐period wave with a duration of 2000 sec or longer was recorded with a very‐broadband system in Pasadena on June 18, 1988. This wave was not observed elsewhere, and is considered of local origin. The acceleration amplitude is 2.5×10−5 cm/sec² in the northwest direction, with the vertical component less than 10% of the horizontal. The horizontal acceleration can be interpreted as due to a tilt of the ground of 2.5×10−8 radians to the northwest. A slowly propagating pressure wave with an amplitude of about 15 mbars could be the cause of the tilt; however, there were no reports suggesting such pressure changes. A more likely cause is a slow tectonic event near Pasadena. The required magnitude of such a slow event is Mw=0, 2, and 4, for a distance of 0.1, 1, and 10 km respectively. This event could be part of a tectonic episode associated with the larger earthquakes which occurred in southern California around this time, especially the December 3, 1988, Pasadena earthquake (ML=4.9) which occurred six months later within 4 km of the Pasadena station.
Regional analysis of D″ velocities from the ray parameters of diffracted P profiles
Authors: Wysession Michael E. , Okal Emile A.
Published: February 2008

In examining the slownesses of linear profiles of diffracted P arrivals, we have discerned regional variations in the compressional velocity structure of D″, the base of the mantle. Three methods of determining the slownesses were tested, concluding that the waveform cross‐correlation (XC) technique is more reliable over a wide range of epicentral distances than methods involving a linear regression through either the first motion or first peak arrival times. XC slownesses suggest a statistically conservative range in D″ average velocities of 3.1%, and reveal regions of very fast velocities under Asia and the eastern Pacific basin and of very slow velocities under the New Guinea/Solomon Islands region. Slownesses were found to correlate well with the tomographic model V3 of Morelli and Dziewonski [1986], derived from a different technique and data set. Synthetic seismograms were generated using a summation of spheroidal normal modes, and at periods greater than 45 s the diffracted waves show much less variation and are very well modeled by PREM.
A theory of electron cyclotron waves generated along auroral field lines observed by ground facilities
Authors: Wu C. S. , Yoon Peter H. , Freund H. P.
Published: February 2008

A generation mechanism for radio waves in the frequency range 150–700 kHz observed by ground facilities is suggested in terms of an electromagnetic electron cyclotron instability driven by auroral electrons. The excited waves can propagate downward along the ambient magnetic field lines and are thus observable with ground facilities. The trapped auroral electrons are supposed to play an important role in the generation process, because they give rise to a thermal anisotropy which consequently leads to the instability. The present work is a natural extension of the theory proposed earlier by Wu et al. [1983] which was discussed in a different context but may be used to explain the observed waves originated at low altitudes (< 0.5 RE). This paper presents a possible wave generation mechanism valid in the entire auroral field line region of interest.
Effects of azimuthal asymmetry on ULF waves in the dipole magnetosphere
Authors: Lee Dong‐Hun , Lysak Robert L.
Published: February 2008

The properties of the coupling of compressional and transverse ULF waves strongly depend on the azimuthal wavenumber m. We investigate these effects in a numerical model of ULF wave propagation in a dipolar magnetosphere. As the azimuthal wave number m becomes larger, the frequencies of the global modes are increased, each coupling location is shifted toward the plasmapause, and the wave energy of global compressional modes in the magnetosphere is confined to a smaller region near the magnetopause. These conclusions are qualitatively consistent with previous analytical and numerical models. It is suggested that the radial dependence of the azimuthal wavelength in the dipole geometry is important to the propagation of compressional waves. This effect is not present in either box or cylindrical models, in which the azimuthal wavelength does not depend on the radial distance, and can be distinguished from effects arising from the inhomogeneity of the Alfven speed. On the other hand, the Alfven shear modes are found to have periods independent of m.
Simultaneous Na lidar and HF radar observations of vertical velocities in the mesosphere above Urbana, Illinois
Authors: Franke S. J. , Beatty T. , Thorsen D. , Liu C. H. , Gardner C. S. , Roesler F. L. , Harlander J.
Published: February 2008

The first simultaneous Na lidar and Medium Frequency (2.66 MHz) Doppler radar observations of vertical winds in the mesosphere (79.5–100 km) above Urbana, Illinois are reported. The lidar and radar systems were operated simultaneously for a 24‐h period during January, 1989. The lidar measured Na density profiles and the radar measured the vertical component of velocity. The Na density data was used to derive the vertical velocity using the continuity equation. This data set provides a unique opportunity to check the consistency of parameters measured by the two very different experimental techniques. Excellent agreement is found between the radar velocities and the velocities inferred from the Na density on the bottomside of the Na layer. Significant differences are found between the velocities obtained with the two techniques on the top side of the Na layer. Possible reasons for this discrepancy are discussed.
Recurring variations of probable solar origin in the atmospheric Δ14C time record
Authors: Hood L. L. , Jirikowic J. L.
Published: February 2008

After removal of the ∼ 11,000‐year geomagnetic contribution to a relatively high‐precision atmospheric Δ14C record covering the past 7200 years, residual variations exhibit a 2200–2600 year quasi‐periodicity that has been recognized in earlier studies. We find here that century‐scale variations in the most recent ‘cycle’ are positively correlated with similar short‐term variations in each of the two previous cycles. Thus the quasi‐periodicity consists of both a long‐term variation of the mean and a superposed, approximately recurring pattern of century‐scale variations. The strongest of these latter variations occur near successive maxima of the ∼ 2400 year cycles. During the last millennium, the largest century‐scale variations (occurring near the most recent 2400 year maximum) are known to be mainly a consequence of the pronounced Maunder, Spörer, and Wolf solar activity minima. Therefore, the recurrence of large amplitude Δ14C variations at 2400 year intervals is most directly explained as due to solar forcing at both the ∼ 2400 year and century‐scale periods. A fully terrestrial 2400 year modulation of an independent century‐scale solar forcing function is disfavored by the joint occurrence of relatively strong Δ14C maxima and solar activity minima during the current millennium, according to independent proxy records. The probable existence of a ∼2400 year solar quasi‐cycle has implications for the predictability of future pronounced solar activity minima and for the interpretation of certain minor Holocene climatic variations.
Factors controlling the photochemical generation of gaseous H2O2 in the Los Angeles atmosphere
Authors: Sakugawa Hiroshi , Tsai Wangteng , Kaplan Isaac R. , Cohen Yoram
Published: February 2008

The factors for controlling the photochemical generation of gaseous H2O2 were studied on the basis of both field data and model predictions. Field data of the concentration of gaseous H2O2 at ground‐level were obtained in west Los Angeles during 1985–88. The results indicate that there is a clear seasonal trend of gaseous H2O2 (0.03–1.35 ppb, n=150) with highest concentrations in the summer. Statistical analyses revealed that the concentration of H2O2 increases with increasing solar radiation at a statistically significant level. A one‐dimensional photochemical model, which is based on the prevailing meteorological conditions and primary pollutants loading in Los Angeles, also predicted that solar radiation is the major factor in determining the formation rate of H2O2 in the atmosphere. These results indicate that solar radiation significantly controls the formation of gaseous H2O2. Considering the low photochemical activity in the winter, H2O2 is probably limiting for the oxidation of SO2 in the Los Angeles winter atmosphere where the SO2 content exceeds the H2O2 concentrations. Our results also imply that, if the UV radiation in the troposphere increases due to the depletion of the stratospheric O3 content, the H2O2 levels will increase and as a result the production of sulfuric acid will increase in the winter atmosphere.
On the implications of an intrinsic magnetic field in early Mars
Authors: Kar Jayanta
Published: February 2008

It is shown that, the intrinsic magnetic field of early Mars was strong enough to deflect the solar wind and form a magnetosphere. The implications of such a magnetosphere earlier in Mars' history are discussed qualitatively from the point of view of atmospheric evolution. Escape of atmospheric constituents through the polar regions could contribute significantly to the atmospheric loss processes inferred from observations.
Broadband F‐k analysis of array data to identify sources of local scattering
Authors: Gupta I. N. , Lynnes C. S. , Wagner R. A.
Published: February 2008

F‐k analyses of short‐period recordings of both U.S. and Soviet underground nuclear explosions at the Eskdalemuir (EKA), Scotland array indicate arrivals from a local source about 15 km due northwest of the array. Use of residual seismograms derived by subtracting the beamed record from each array channel confirmed the presence of the same scatterer. The secondary seismic source appears to be short‐period surface waves due to the scattering of incident P waves at a nearby deep valley known as Moffat Water, in agreement with Key's (1967) results. Similar analyses of the NORESS (Norway) array data from U.S. and Soviet nuclear shots also indicate secondary arrivals suggesting a local near‐surface scatterer about 25–30 km southwest of the array, in the region of Lake Mjosa. Thus, short‐aperture array data can be useful in identifying and locating sources of near‐receiver scattering.
Lower mantle velocity inhomogeneity observed at GRF array
Authors: Davis J. Peter , Weber Michael
Published: February 2008

GRF broadband array recordings provide strong support for the existence of anomalous P‐coda phases along the Kuriles ‐ European path first observed using WWSSN data. The data suggest that the phase, termed here PdP, arrives 3–5s after the direct P‐wave and has a slowness 0.7–0.8 s/deg smaller. The latter measurement precludes PdP's misidentification as a source stopping phase, and given the magnitude of the slowness difference, slab multipathing and diffraction are equally unlikely. Because the phase is clearly not observed for all Kurile events and from timing and geometric considerations, crustal reverberations are also untenable as an explanation for PdP's appearance. The hypothesis which best explains the PdP arrival time, arrival angle, and waveform is the presence of a 3% velocity jump in the lower mantle approximately 290 km above the core‐mantle boundary. Because of the failure of other studies to observe PdP under favorable recording conditions, the reflector must be of limited regional extent beneath Northern Siberia.
The vapor pressures of supercooled HNO3/H2O solutions
Authors: Hanson David R.
Published: February 2008

A procedure utilizing the Gibbs‐Duhem relation is used to extrapolate vapor pressures of supercooled HNO3 mixtures to 190 K. Values of A and B from the equation logP = A − B/T are presented for nitric acid solutions between 0.20 and 0.25 mole fraction HNO3. In the stratosphere, if sufficient HNO3 vapor is present because it has not come into equilibrium with the nitric acid trihydrate, supercooled nitric acid solutions could condense at temperatures up to 1.5 ±0.8 K above the ice point.
Denitrification of the polar winter stratosphere: Implications of SAM II cloud formation temperatures
Authors: Hamill Patrick , Toon O. B.
Published: February 2008

We use the SAM II extinction profiles and the associated temperature profiles to determine the amount of denitrification of the winter polar stratospheres. We see clear evidence of the denitrification process in the Antarctic data. There are indications in the Arctic data that denitrification mechanisms may be at work there also. At the latitudes observed by the SAM II satellite system, denitrification begins before the formation of extensive ice clouds and may be due to sedimentation of nitric acid particles. However, we cannot exclude the possibility of denitrification by type II PSC's at latitudes not observed by SAM II.
Comment on “Detection of multiply deuterated methane in the atmosphere”
Authors: Kaye Jack A. , Jackman Charles H.
Published: February 2008

It has recently been reported [Mroz et al., 1989] that the abundance of mass‐20 isotopes of methane (CH4), which correspond to either of the highly deuterated forms 12CD4 or 13CHD3, is some 500 times that expected based on the statistical combination of H, D, 12C, and 13C and observed CH4 amounts. These authors then suggested that it is possible that the enhanced concentration of these species is due to their longer lifetimes than that of CH4 itself because of their slower rate of loss by reaction with the hydroxyl radical (OH). We have tested this hypothesis with a two‐dimensional atmospheric chemical‐dynamical model and found that no large enhancements of 13CHD3 and 12CD4 can result in this way; in the troposphere enhancement factors of between 4 and 5 and between 7 and 8, respectively, were found, with enhancements becoming only slightly larger (14 and 25, respectively) in the stratosphere. The factor of 500 enhancement reported by Mroz et al. must have other origins.
Asymmetric propagation of surface waves on the aspherical Earth
Authors: Tsuboi S.
Published: February 2008

We investigate anomalies of both the phase velocity and the amplitude of surface wave that depend on the direction traversed along the great circle. Pairs of observed Rayleigh wave packets are convolved to show that the great circle phase velocity may depend on the propagation direction. We calculate synthetic seismograms using the eigensolutions obtained by the variational method to see if these anomalies are reproduced by present laterally heterogeneous earth models. The results show that present models can reproduce these anomalies qualitatively.
Thermal expansion of mantle minerals at high pressures—A theoretical study
Authors: Reynard Bruno , Price Geoffrey D.
Published: February 2008

Recent experimental work has shown that the pressure dependence of the thermal expansion coefficient can be expressed as:

 

where δT, the Anderson‐Gruneisen parameter, is assumed to be independent of pressure, and for the materials studied has a value that lies between 4 and 6. Calculation of δT from seismic data, however, appears to suggest a contradictory value of between 2 and 3 for mantle‐forming phases. Using an atomistic model based on our previously successful many‐body interatomic potential set (THBl), we have performed calculations to obtain values of δT for four major mantle‐forming minerals. Our model results are in excellent agreement with experimental data, yielding values of between 4 and 6 for forsterite and MgO, and values in the same range for MgSiO3−perovskite and γ‐Mg2SiO4. Moreover, the calculations confirm that δT is indeed constant with pressure up to the core‐mantle boundary. The apparent conflict between the values of δT predicted from seismic data and those obtained from experiment, and now from theory, is discussed.
Atmospheric contamination: A possible source for heavy noble gases in basalts from Loihi Seamount, Hawaii
Authors: Patterson D. B. , Honda M. , McDougall I.
Published: February 2008

Re‐evaluation of available noble gas data obtained from the glassy rims of basalts from Loihi Seamount, Hawaii, shows that contamination of magmas prior to eruption, by addition of a significant component of atmosphere‐derived heavy noble gases, is a plausible explanation for the observed atmosphere‐like isotopic compositions of Ne, Ar, Kr, and Xe. The most likely source for the atmospheric component is interaction of the magma with seawater carrying dissolved atmosphere‐derived noble gases.

The possibility of a significant atmospheric component in Loihi samples suggests that the observed heavy noble gas compositions may not be representative of the mantle source of Loihi magmas. While leaving open the question of the noble gas composition in the source region, atmospheric contamination provides a valid alternative to the interpretation that the mantle source region of Loihi magmas has an atmosphere‐like noble gas composition.
VLF heating of the lower ionosphere
Authors: Inan Umran S.
Published: February 2008

A controlled wave‐injection experiment with a 28.5 kHz transmitter having a radiated power of 100 kW has revealed evidence of ionospheric heating by the VLF waves. Calculations indicate that the observed effect can be attributed to the absorption of wave energy in the lower ionosphere, which is estimated to result in a 30% enhancement in the collision frequency at 85 km. This process also represents a new means of direct coupling of lightning energy to the lower ionosphere.
Highly nonlinear magnetic pulses at comet Giacobini‐Zinner
Authors: Tsurutani Bruce T. , Smith Edward J. , Matsumoto Hiroshi , Brinca Armando L. , Omidi Nojan
Published: February 2008

Nonlinear solitary magnetic pulses have been detected near the outbound bow shock/wave of Comet Giacobini‐Zinner. The pulses have peak field‐to‐background compression ratios ranging from 2.3 to 7.0 and full‐width half‐maximum durations from 12 to 72s, comparable to the H2O group ion gyroperiod. The waves air nearly circularly polarized and typically propagate at large angles (55°–75°) relative to the ambient magnetic field. The waves are all right‐hand polarized in the spacecraft frame, independent of their direction of propagation relative to the solar wind.

Because all of the solitary waves have the same spacecraftframe polarizations, one interesting hypothesis is that the waves may have phase speeds greater than the solar wind speed The role that the waves may play with the bow shock is discussed briefly.
The lower hybrid drift instability at the magnetopause
Authors: Gary S. Peter , Sgro A. G.
Published: February 2008

When the interplanetary magnetic field is northward, wave‐particle cross‐field transport may contribute to solar wind‐magnetosphere coupling. Such transport is studied here through the use of hybrid computer simulations (particle ions, fluid electrons with nonzero mass) carried out in the x‐y plane of a plasma with a density gradient in the x direction, no average iow speed, and a magnetic field B = B(x)ž. At early times, the lower hybrid drift instability grows on the gradient. However, at times long compared to an ion gyroperiod, the fluctuations coalesce to longer wavelengths in the y‐direction and nondiffusive density x‐profiles emerge which exhibit “plateaus” and “inclusions” qualitatively similar to those observed by ISEE near the magnetopause. These results call into question critical assumptions of quasilinear theories of cross‐field transport by this instability.
IMP‐8 observations of traveling compression regions: New evidence for near‐Earth plasmoids and neutral lines
Authors: Slavin J. A. , Lepping R. P. , Baker D. N.
Published: February 2008

An examination of IMP‐8 tail lobe magnetic field measurements has been conducted to determine whether the traveling compression region (TCR) phenomena detected by ISEE‐3 in the distant geotail, and believed to be caused by tailward moving plasmoids, are present closer to the earth. The study produced 16 examples of TCRs at distances of X = −31 to −37 RE. For two events considered in detail TCRs were observed in close association with substorm growth phase signatures in the lobes. The lengths of these TCRs are estimated to be 8–12 RE. It is our conclusion that the IMP‐8 TCR observations provide new evidence that small plasmoids and, hence, multiple reconnection neutral lines can exist earthward of X = −35 RE.
Atmospheric signals at high latitudes in a coupled ocean‐atmosphere general circulation model
Authors: Currie Robert G. , Hameed Sultan
Published: February 2008

We report evidence for a ca. 40 month signal in air pressure simulated in a general circulation model, together with two further natural signals previously found, the ca. 26 month quasi‐biennial oscillation (QBO) and the ca. 14 month atmospheric Chandler tide. These 3 natural signals interact with the annual cycle and its harmonics to create a rich spectrum of summation and difference tones. Theoretically we expect 33 tones to be produced and evidence for 29 of these is found. The three classes of signals combined to contribute 51% of total variance, and range in period from 2 to 68 months. These results indicate that the spectrum of atmospheric variations on these time scales is discrete, unlike that of a chaotic system.
Directional variations in thermal emission from geologic surfaces
Authors: Jakosky Bruce M. , Finiol Gary W. , Henderson Bradley G.
Published: February 2008

We investigated the directional emission properties of geologic surfaces using a ground‐based, hand‐held infrared radiometer and thermistor probe. Field sites involved surfaces ranging from smooth playa and sand surfaces to a very rough aa lava flow in the Lunar Crater Volcanic Field, NV, as part of the Geological Remote Sensing Field Experiment. Large directional variations in thermal emission were found; they result from the presence of surface roughness–at large scales producing spatial variations in kinetic temperature and at small scales producing emissivity variations. These variations are important in remotely determining surface structure and understanding surface energy balance and emission spectra.
the pulsating cusp
Authors: Smith M. F. , Lockwood M.
Published: February 2008

Recent observations at the magnetopause and of the high‐latitude ionosphere, suggest that the cusp may be pulsed in nature. Specifically ground‐based observations in the dayside auroral oval reveal transient optical features accompanied by bursts of enhanced plasma flow. Also, recent interpretation has shown cusp satellite data to be consistent with a burst of enhanced reconnection. In this paper we use these observations to produce a scenario in which both the satellite and ground‐based observations can be fitted. The scenario we develop is based on the flux transfer event (FTE) models of Southwood et al. and Scholer and shows that the signatures, at both low and high altitudes, can be interpreted in terms of FTEs.
The September 29, 1989 ground‐level event observed at high rigidity
Authors: Swinson D. B. , Shea M. A.
Published: February 2008

Ground‐level solar cosmic ray events are usually observed by high latitude neutron monitors at relatively low rigidities (> 1 GV) and are not usually observed by underground cosmic ray detectors because of their much higher threshold rigidity. However, the September 29, 1989 ground‐level event was sufficiently large and unusual that it was recorded by the Embudo, New Mexico underground muon telescope which has a threshold rigidity of 19 GV. The observed increase was 2.2 ± 0.2% in the hour interval from 1100 to 1200 UT. There was no statistically significant increase in the data from the Socorro underground muon telescope which has a threshold rigidity of 45 GV. This is the first detection of a ground‐level solar cosmic ray event by any underground cosmic ray muon telescope where the event has been clearly distinguishable above the background cosmic ray intensity.
Pyridinium ions and pyridine in the free troposphere
Authors: Schulte P. , Arnold F.
Published: February 2008

Composition measurements of atmospheric positive ions were made in the middle troposphere (3000 – 6000 m) above central Europe using an improved aircraft‐borne mass spectrometer. The by far most abundant “core ion” species was found to be protonated pyridine (H+C5H5N) whose identification is strongly supported by in‐flight ECD (electric field induced collisional dissociation) studies of this ion resulting in fragment ions which are characteristic for H+C5H5N. ACIMS (active chemical ionisation mass spectrometry) studies carried out on the same flights independently reveal the presence of a trace gas consistent with pyridine posessing a mole fraction of 1.6 pptv (parts per trillion by volume) at about 4000 m altitude. The formation mechanism of H+C5H5N is briefly discussed.
The correlation of tropospheric and stratospheric temperatures and its effect on the detection of climate changes
Authors: Liu Qing , Schuurmans Cornelius J. E.
Published: February 2008

Based on 42 years of seasonal mean temperature anomalies of the troposphere and stratosphere in De Bilt, the Netherlands, we find that the tropospheric and lower stratospheric temperatures are inversely correlated. The high stratospheric temperatures are apparently uncorrelated with tropospheric temperature. The inverse correlation of tropospheric and lower stratospheric temperatures is most apparent in summer. This correlation is associated with the prevailing weather systems, the warm troposphere seasons are associated with more high pressure systems, the cold troposphere seasons are associated with more lower pressure systems, being consistent with the Dines' relationship (Dines, 1919). We point out that the small warming trends in the troposphere and cooling trends in the lower stratosphere from the middle sixties to 1985 are not evidently caused by the greenhouse effect, as the internal fluctuations of the atmosphere‐ocean system can also create the same trends. We think that it is until now (maybe even in the near future), impossible to find any reliable evidence of climatic change by searching for the combined signal of the tropospheric warming and stratospheric cooling. Another way of detecting the climatic changes is to search for the signal of the increase of the lower stratospheric cooling with increasing altitude. We will show that this method may be able to separate the climatic change due to the external forces from the atmospheric internal fluctuations.
Thermal pressure in the laser‐heated diamond anvil cell
Authors: Heinz Dion L.
Published: February 2008

Estimation of the thermal elastic effect is necessary for the calibration of the pressure and temperature conditions during laser‐heated diamond anvil cell experiments, since above 800K, the standard technique of using ruby florescence to measure pressure fails. Continuum calculations based upon the thermoelastic equations for an elastic medium were used to estimate the thermal pressure resulting from a radially symmetric temperature gradient in an elastic sphere with zero displacement on its surface. This calculation corresponds to the thermal pressure generated in a laser‐heated diamond anvil cell sample that is compressed without a pressure medium. This solution must fall between circumstances where the sample is held at constant pressure and where the sample is held at constant volume. It is shown here that the thermal pressure in an elastic medium with a Gaussian temperature gradient is approximately 40–60% of the thermodynamic value of the thermal pressure in a material raised to some constant temperature with the volume constrained to be constant. Even though the thermal pressure correction can be significant in terms of the total pressure that the sample experiences, these calculations indicate that the correction can be estimated to approximately 10%.
Source characteristics of the Loma Prieta, California, Earthquake of October 18, 1989 from global digital seismic data
Authors: Choy George L. , Boatwright John
Published: February 2008

Displacement, velocity and acceleration records of P and SH body waves recorded at teleseismic distances are analysed to determine the static and dynamic source parameters of the Loma Prieta, California earthquake of October 18, 1989 (mb 6.6, Ms 7.1). Three distinct bursts of energy corresponding to three subevents can be recognized in most records. The displacement waveforms indicate that the first subevent contributes negligible moment while the largest releases of moment and energy are controlled by the second and third subevents. The second and third subevents are located north and south of the initial nucleation. A fourth small subevent needed to model later features of the P waveforms suggests that slow slip continued after the major releases of energy occurred. The waveforms are fit with a fault plane solution having strike 130°, dip 65° and slip 140° for all the subevents. The focal depths of the two major subevents are 16 and 12 km, and their asperity radii are 4.0 and 6.0 km, respectively. The seismic moment, M0, is 2.2×1026 dyne‐cm. From spectral analysis of teleseismic velocity, the radiated energy, Es, is estimated to be 1.1×1022 dyne‐cm, implying an apparent stress of 15 bars. From the high‐frequency level of the teleseismic acceleration spectrum and a rupture area of 440 km2, we derive a dynamic stress drop of 51 bars.
Thermospheric dynamics at the South Pole
Authors: Hernandez G. , Smith R. W. , Roble R. G. , Gress J. , Clark K. C.
Published: February 2008

A self‐aligning Fabry‐Perot spectrometer has been installed at Amundsen‐Scott Station, Antarctica (Geographic South Pole) and has been used to determine neutral upper thermosphere winds and temperatures, obtained from the measurement of the Doppler shift and Doppler width of the line profiles of the [OI] 15,867 K (630 nm) line emission, during the austral winter of 1989 (April 1989 to September 1989). These first ground‐based measurements of F‐region neutral dynamics at the South Pole, show a rich variety of dynamic phenomena and strong couplings with the ionospheric plasma. Data for two contrasting days in April 1989 are presented here. The data of April 23 UT illustrate the diurnal variations of winds and temperatures during geomagnetic quiet‐to‐moderate conditions, while the data of April 27 UT illustrate diurnal variations during geomagnetically disturbed periods. These data are compared with the average pattern obtained at a similar geomagnetic latitude and conditions, but in the Northern Hemisphere (Longyearbyen, Spitsbergen) and with predictions of the average dynamics in the South Pole region made by the NCAR thermosphere‐ionosphere general circulation model (TIGCM). The measured winds at the South Pole have a stronger prevailing westward component in its diurnal cycle than is either observed at Longyearbyen (in the Northern Hemisphere) or predicted at South Pole by the TIGCM.
Heterogeneous chemistry on liquid sulfate aerosols: A comparison of in situ measurements with zero‐dimensional model calculations
Authors: Mather J. H. , Brune W. H.
Published: February 2008

The possibility that stratospheric chlorine is converted from reservoir to reactive forms by heterogeneous reactions on background sulfate aerosols is examined. Tightly constrained photochemical models have been used to calculate [ClO] for the morning and the afternoon conditions observed on January 24, 1989 outside the Arctic polar vortex by instruments on the NASA ER‐2 aircraft. Calculations involving gas‐phase chemistry only and calculations with heterogeneous chemistry including HCl evaporation from the aerosol both produce ClO abundances that agree with observations; calculations in which HCl removal from the aerosol is controlled by heterogeneous reactions produce ClO abundances that are 3 to 3.5 times larger than observations. These results suggest that HCl evaporation must be included in a model of the chemistry of background aerosols. As a result, heterogeneous chemistry on background aerosols is inefficient for the direct conversion of chlorine to its reactive forms throughout most of the stratosphere. However, the background aerosols can be effective at converting NOx to HNO3, and thus by homogeneous chemistry, a ClO enhancement of a factor of two at midlatitudes can result.
Measurement of isotopic abundances in collected stratospheric ozone samples
Authors: Schueler B. , Morton J. , Mauersberger K.
Published: February 2008

Enrichment of heavy O3 isotopes has been measured in collected stratospheric samples. A balloon‐borne cryogenic sampler was used to gather six O3 samples between 26 and 35 km in three flights. Subsequent laboratory mass spectrometer analysis of rare O3 isotopes at both mass 49 and 50 has resulted in more precise measurements than have previously been reported with in situ and ground‐based techniques. In one flight, 50O3 was enriched by 12–16% and 49O3 by 9–11%, both increasing with altitude. In the remaining two flights, the isotope enrichment was nearly mass‐independent at 8–9%. The enrichments in O3 at mass 50 are less than the large 40% value observed in some stratospheric measurements but similar to 49O3 and 50O3 fractionations produced in laboratory‐generated ozone.
Carbon dioxide emissions from Deccan Volcanism and a K/T boundary Greenhouse Effect
Authors: Caldeira Ken , Rampino Michael R.
Published: February 2008

A greenhouse warming caused by increased emissions of carbon dioxide from the Deccan Traps volcanism has been suggested as the cause of the terminal Cretaceous extinctions on land and in the sea. We estimate total eruptive and noneruptive CO2 output by the Deccan eruptions (from 6 to 20 × 1016 moles) over a period of several hundred thousand years based on best estimates of the CO2 weight fraction of the original basalts and basaltic melts, the fraction of CO2 degassed, and the volume of the Deccan Traps eruptions. Results of a model designed to estimate the effects of increased CO2 on climate and ocean chemistry suggest that increases in atmospheric pCO2 due to Deccan Traps CO2 emissions would have been less than 75 ppm, leading to a predicted global warming of less than 1°C over several hundred thousand years. We conclude that the direct climate effects of CO2 emissions from the Deccan eruptions would have been too weak to be an important factor in the end‐Cretaceous mass extinctions.
Tectonics of Lakshmi Planum, Venus: Tests for Magellan
Authors: Grimm Robert E. , Phillips Roger J.
Published: February 2008

The origin of Lakshmi Planum and its surrounding mountain belts remains an important unresolved element in the global tectonic framework of Venus. From the perspective of gravity signature and potential driving forces, the mantle upwelling model is the simplest and its principal failure, that it cannot produce radial shortening on the uplift periphery, may be resolved if the lithosphere is laterally heterogeneous. Our preferred model consists of a hot mantle plume rising beneath a pre‐existing block of tessera. The lithosphere is weakened at this hotter and presumably thicker crust, and the outward near‐surface flow is attenuated at the peripheral discontinuity in lithospheric strength. Crustal thickening and mountain belt formation occur there. We propose several criteria to test this “tessera‐plume” model together with its competitors at the higher resolution in both imaging and gravity afforded by the Magellan mission.
The radar scattering characteristics of Venus landforms
Authors: Ford Peter G. , Senske+ David A.
Published: February 2008

Nine geologic units are identified in a recently published Arecibo image of the Venus equatorial region [Campbell, et al., 199O]. A detailed examination of the radar scattering properties of these units using data from the imaging mode of the Pioneer Venus Radar Mapper (PVM) shows them to fall into three distinct classes: 1) dark plains, 2) tessera, narrow‐spaced parallel lineaments, and bright and dark banded terrain, and 3) bright plains, mottled plains, ovoids, lineament belts, and edifices. Additional units interpreted to be analogous to those mapped from the Arecibo data are identified in the region imaged exclusively by PVM, and are found to have similar scattering properties. An examination of the scattering properties of units mapped as tessera—Tellus Regio and eastern Beta Regio, as compared with the northern flanks of Thetis Regio—leads to the conclusion that part of Thetis possesses characteristics similar to Tellus.
Imaging of discontinuities in nonlinear 3‐D seismic in‐version
Authors: Carrion Philip M. , Červený Vlastilav
Published: February 2008

We present a nonlinear approach for reconstruction of discontinuities in geological environment (earth's crust, say). The advantage of the proposed method is that it is not limited to a Born approximation (small angles of propagation and weak scatterers). One can expect significantly better images since larger apertures including wide angle reflection arrivals can be incorporated into the imaging operator. In this paper, we treat only congressional body waves: shear and surface waves are considered as noise.