bluuebunny/crossref_metadata_2025 huggingface dataset:
Energetic particle characteristics of magnetotail flux ropes
Authors: Scholer M. , Klecker B. , Hovestadt D. , Gloeckler G. , Ipavich F. M. , Galvin A. B.
Published: February 2008

During the recent ISEE‐3 Geotail Mission three events have been identified from the magnetometer data which are consistent with a spacecraft crossing of a magnetotail flux rope. We present energetic electron and proton observations obtained by the Max‐Planck‐Institut/University of Maryland sensor system during two of the possible flux rope events. During one event remote sensing of the flux rope with energetic protons reveals that the flux rope is crossed by the spacecraft from south to north. This allows determination of the handedness of the magnetic field twist and of the flux rope velocity relative to the spacecraft. A minimal flux rope radius of 3 RE is derived. Energetic proton intensity is highest just inside of the flux rope and decreases towards the core. Energetic electrons are streaming tailward near the outer boundary indicating openess of the field lines and are isotropic through the inner part of the flux rope.
The effects of transient rheology on the interpretation of lower mantle viscosity
Authors: Sabadini R. , Yuen D. A. , Gasperini P.
Published: February 2008

We have reexamined the role played by transient rheology in the interpretation of mantle viscosity. This investigation has been carried out by comparing the amplitude responses with the data of secular variation of, the relative sea‐level histories at sites well within the ice margins and at the ice margin like the city of Boston. A linear Burgers’ body rheology has been assumed in the lower mantle. The data near the edge of the ice load proves most sensitive to the transient viscosity structure. The non‐monotonic behavior of sea‐level data near Boston can be explained both by a steady‐state lower mantle viscosity of 1022P with a thick lithosphere and also by a transient lower mantle rheology but with a thin lithosphere. The long‐term viscosity of the lower mantle in this second model has a steady‐state value of around 5×1023P.
On the efficiency of the Cowling mechanism in the auroral electrojet
Authors: Yasuhara F. , Kamide Y. , Vickrey J. F.
Published: February 2008

By using Chatanika radar measurements of the ionospheric electric field and conductivity, an attempt is made to estimate the extent to which the Cowling mechanism is taking place in the westward auroral electrojet. We assess the effectiveness of this mechanism in terms of the ratio α = IPS/IHN, where IHN and IPS are the northward Hall and the southward Pedersen currents, respectively. Estimates of α are made for regions in which the electric field had both westward and southward components in the midnight sector during high geomagnetic activity. It is found that α varies considerably with latitude within the westward electrojet and that α decreases with increasing IHN. Assuming east‐west uniformity of the associated ionospheric quantities, these variations indicate that significant portions of the charges carried by the northward Hall current (due to the westward electric field) are removed from the "excess" charge region without generating an intense polarization field. This implies that the classical Cowling mechanism is taking place only incompletely.
Further observations of X‐rays inside thunderstorms
Authors: McCarthy M. , Parks G. K.
Published: February 2008

A control and an x‐ray detector were flown into thunderstorms in 1984. The x‐ray detector found statistically significant radiation flux increases in the energy range 5 to > 110 keV for time intervals of several seconds each. Simultaneously the control detector showed no statistically significant changes. The x‐ray flux is sometimes seen to increase prior to observed lightning discharges and then return to background levels within 0.1 seconds of a lightning flash initiation. The temporal development of these x‐ray bursts is discussed and related to inferring the scale size of the x‐ray emitting regions.
On spacecraft‐induced optical emission:A proposed second surface luminescent continuum component
Authors: Prince R. H.
Published: February 2008

The status of observations and current theories of spacecraft‐induced optical emission (ram glow) from the Atmospheric Explorer‐C satellite to the most recent shuttle missions is reviewed. To resolve the discrepancy between the observed spectral continuum and the most likely gas‐phase emitter, the NO2 continuum, a second continuum is proposed, lying further to the red and due to true surface emission (chemiluminescence) as a consequence of atomic and molecular oxygen adsorption. An altitude variation modelled on the basis of this mechanism, using laboratory data, offers good agreement with observations by the AE‐E satellite, and is capable of producing the quantitative intensities in general.
New results on the generation of broadband electrostatic waves in the magnetotail
Authors: Grabbe Crockett L.
Published: February 2008

The theory of the generation of broadband electrostatic noise in the magnetotail is extended through numerical solution of the dispersion relation under conditions that exist in the plasma sheet boundary layer. It is found that the low‐frequency portion of the spectrum has a broad angular spectrum but a fairly sharp peak near 75° with respect to the magnetic field, while the high‐frequency portion has a narrower angular spectrum that is strongly concentrated along the magnetic field line. These results are in excellent agreement with observations of the broadband wave spectrum and a recent measurement of the propagation direction. The effect of a second cold component of electrons is analyzed, and it is found that it can increase the upper cutoff frequency of BEN to the observed value at about the plasma frequency.
Secondary magnetization of Triassic‐Jurassic volcaniclastic rocks of the Quesnel Terrane, Quesnel Lake, B.C.
Authors: Rees Chris J. , Irving E. , Brown Richard L.
Published: February 2008

Upper Triassic‐Lower Jurassic rocks at Quesnel Lake form part of the Quesnel terrane, which was emplaced against the Omineca Belt, part of the North American (paleo‐)continental margin, in the late Early Jurassic. Hard magnetizations, which may or may not be primary, were identified in volcanic wackes, but they are poorly grouped. However, removed magnetizations of intermediate unblocking temperatures (200‐500°C) and coercivities (30‐50 mT) are systematically directed northeast and downward (D=35°, I=57°, a95=9° 5 sites, 22 specimens; paleopole 62°N, 15°W, dm=13°, dp=10°) with respect to present horizontal. We interpret this to be an overprint, acquired after Middle to Late Jurassic folding, as a result of mid‐Cretaceous plutonism during the Cretaceous Normal Superchron. The paleopole is compatible with Early to mid‐Cretaceous paleopoles from other terranes in the southern Canadian Cordillera, but does not agree with observations from post‐Jurassic cratonic rocks. This disagreement indicates that in the mid‐Cretaceous these terranes, along with at least part of the Omineca Belt to which they were attached, formed a quasi‐rigid super‐terrane which was situated about 2000 km farther south than its present position relative to the craton.
Stability of phase B, A hydrous magnesium silicate, to 2300°C at 20 GPA
Authors: Kato Takumi , Kumazaw Mineo
Published: February 2008

The stability of phase B, hydrous magnesium silicate (Mg23Si8O42H6), has been investigated experimentally up to 20 GPa and 2500°C. Phase B is synthesized by heating a powder mixture of forsterite and periclase under hydrous conditions at pressures above 15 GPa, and temperatures above 1500°C, and is stable up to its incongruent melting temperature (2300°C at 20 GPa), above which it decomposes into an assemblage of liquid and periclase. The remarkable stability of phase B indicates the possibility of its presence as a host for H2O in the deep upper mantle of the Earth.
Initial results from the DE‐1 ozone imaging instrumentation
Authors: Keating G. M. , Craven J. D. , Frank L. A. , Young D. F. , Bhartia P. K.
Published: February 2008

The first synoptic global‐scale images of total column ozone are obtained in the sunlit hemisphere using the imaging instrumentation on board the spacecraft Dynamics Explorer 1 (DE‐1). The total column ozone is determined using the backscatter ultraviolet technique. The high apogee altitude of the eccentric, polar orbit allows global‐scale images of the terrestrial ozone field to be obtained in 12 minutes with good spatial resolution. Previous ozone‐monitoring spacecraft have required much longer time periods for comparable spatial coverage because of their lower altitudes. The much higher altitude of DE‐1 also provides hours of continuous imaging of features, as compared to minutes or seconds with previous spacecraft. Substantial short‐term (less than 1 day) variations in the synoptic ozone field have been detected. This paper provides a brief description of this unique observation platform and shows the validity of the measured fields using comparisons with the Dobson network and with various meteorological measurements.
On the feasibility of quantitative analysis of atmospheric OH by titration
Authors: Prinn Ronald G.
Published: February 2008

A method is proposed for quantitative analysis of atmospheric OH using a titration technique. The method uses a mixture of two gases: the titrant gas which is destroyed predominantly by reaction with OH on a time scale of a few days or less; and the dispersant gas which is inert essentially and is used to determine the dispersion rate of the mixture once it is released into the atmosphere. The rate of change of the ratio of the concentrations of the titrant and dispersant gases can be related to the local OH concentration. Measurements of this ratio are made for an hour or so after release of the mixture. A hypothetical example is given which utilizes a mixture of two halocarbons measured using a gas chromatograph with an electron‐capture detector.
The ¹D‐³S transition in atomic oxygen: A new method of measuring the O abundance in planetary thermospheres
Authors: Meier R. R. , Conway R. R.
Published: February 2008

The forbidden 2p4 ¹D ‐ 3s ³So transition of atomic oxygen at 1641 Å has been identified in the satellite dayglow spectrum of Huffman et al. (1980). By modelling the optically thick ³P ‐ ³S 1304 Å transition, a probability of 5.4 × 10−6 is determined for ³So atoms branching to the ¹D state rather than to the ³P ground state. The ratio of the 1641 Å to 1304 Å intensities is found to be a linear function of the atomic oxygen abundance; therefore the ratio can be used to determine the O concentration in optically thick planetary thermospheres.
ISEE 1 and 2 observation of the spatial structure of a compressional Pc5 wave
Authors: Takahashi Kazue , Russell Christopher T. , Anderson Roger R.
Published: February 2008

A compressional Pc5 wave was observed on an ISEE 1 and 2 outbound path on September 28, 1981 at L = 5.6‐7.3 near the magnetic equator at ∼10 hr local time during the recovery phase of a geomagnetic storm. The wave propagated westward with a large azimuthal wave number of ∼30 and exhibited in‐phase oscillations of plasma density and magnetic field magnitude. During this event, component‐dependent variations in phase and amplitude were observed for the magnetic field oscillations. The radial and compressional components had a constant phase and their amplitude was finite. In contrast, the azimuthal component changed its phase by 180° and its amplitude became zero during the middle of the wave event. We interpret this observation as indicating the spatial structure of the Pc5 wave. The polarization reversal is likely to be caused by a crossing of a node of a standing wave located 4° above the geomagnetic equator.
Ion acceleration in quasi‐perpendicular collisionless magnetosonic shock waves with subcritical Mach number
Authors: Ohsawa Yukiharu , Sakai Jun‐ichi
Published: February 2008

A self‐consistent evolution of quasi‐perpendicular collisionless laminar magnetosonic shock waves with subcritical Mach number is investigated by using a 2‐1/2 dimension, relativistic, electromagnetic particle code with full ion and electron dynamics. It is shown that significant ion acceleration occurs within the shock ramp by resonant interactions. The ions are heated primarily in the direction perpendicular to a magnetic field. Our results are in good agreement with the recent observations of interplanetary shocks by ISEE spacecraft.
The location of the subsolar bow shock of Venus: Implications for the obstacle shape
Authors: Russell C. T. , Luhmann J. G. , Phillips J. L.
Published: February 2008

The rise in periapsis altitude with time has allowed the Pioneer Venus spacecraft to begin probing the subsolar Venus bow shock. This has allowed the altitude of the subsolar bow shock to be determined by in situ observations for the first time. The observed altitude of 2280 km at the nose together with the previously determined terminator altitude can be used to infer the shape of the obstacle using the gas dynamic model of the solar wind interaction with Venus. When this shape is compared to the measured locations of the Venus ionopause (defined as the point where the magnetosheath magnetic field pressure and ionospheric thermal pressures are equal), it is found that the observed ionopause position is too low to qualify as the obstacle. We infer that a layer of the mass loaded plasma in the magnetosheath forms the magnetic barrier.
Upper limits for stratospheric H2O2 and HOCℓ from high resolution balloon‐borne infrared solar absorption spectra
Authors: Larsen J. C. , Rinsland C. P. , Goldman A. , Murcray D. G. , Murcray F. J.
Published: February 2008

Solar absorption spectra from two stratospheric balloon flights have been analyzed for the presence of H2O2 and HOCℓ absorption in the 1230.0 to 1255.0 cm−1 region. The data were recorded at 0.02 cm−1resolution during sunset with the University of Denver interferometer system on October 27, 1978 and March 23, 1981. Selected spectral regions were analyzed with the technique of nonlinear least squares spectral curve fitting. Upper limits of 0.33 ppbv for H2O2 and 0.36 ppbv for HOCℓ near 28 km are derived from the 1978 flight data while upper limits of 0.44 ppbv for H2O2 and 0.43 ppbv for HOCℓ at 29.5 km are obtained from the 1981 flight data.
Observations of middle atmospheric CH4 and N2O vertical distributions by the Spacelab 1 Grille Spectrometer
Authors: Muller C. , Vercheval J. , Ackerman M. , Lippens C. , Laurent J. , Lemaitre M. P. , Besson J. , Girard A.
Published: February 2008

Methane and nitrous oxide have been observed by limb absorption spectrometry using the Spacelab One grille spectrometer. The CH4 ν3 band is obsserved with a 0.1 cm−1 resolution up to 80 km while N2O can be seen up to 52 km in strong lines of its ν3 band. The values are compared, where possible, with previous observations and are in agreement with rocket determinations.
Time‐series measurements of hydrothermal activity on northern Juan De Fuca Ridge
Authors: Johnson H. Paul , Tunnicliffe Verena
Published: February 2008

During August/September 1984, the submersible ALVIN visited a large, active hydrothermal system on the Juan de Fuca Ridge. A time‐lapse camera, taking photographs every 42 minutes for six days, was deployed at an active vent to characterize the dynamic nature of this system. This report documents the growth rate of a low temperature (measured at 56°C) hydrothermal deposit and establishes that this growth is not constant; periods of substantial erosion are superimposed upon the general growth pattern. Quantitative photographic interpretation of the suspended particulate load suggests a strong diurnal component to these fluctuations. Water flow, manifest by the movement of attached worm tubes, also shows strong variations but on a semi‐diurnal basis correlated to tidal motions.
The structure of young oceanic crust near a very fast spreading ridge
Authors: McClain James S. , Atallah Carl A.
Published: February 2008

We have modeled the structure of the young oceanic crust near the fastest spreading ridge ever to be profiled using seismic refraction techniques. The data were originally collected during the Capricorn expedition of the Scripps Institute of Oceanography in 1953. One of the split leg profiles from that expedition, C22, was conducted near the East Pacific Rise at 15°S, where the half spreading rate is over 80 mm/yr. By digitizing the data, and modeling the two splits of C22 using synthetic seismograms, we have found that the crust is normal in thickness (5 to 7 km) and in velocity structure. An upper crustal transition zone is present on both legs and would appear to be a regular feature of young oceanic crust. It is probably too deep (1.5 to 2 km beneath the seafloor) to be correlated with the boundary between pillow basalts and sheeted dikes. Instead, we attribute this transition zone to changes in crustal porosity and/or hydrous minerals in the oceanic crust. From the appearance of wide‐angle moho reflections near the rise axis, we suggest that the very large crustal magma chamber that might be expected under this fast spreading ridge is not present. This presumably results from the cooling of the crust by pervasive hydrothermal circulation.
Systematics of Ti isotopes in carbonaceous chondrite whole‐rock samples
Authors: Niemeyer S.
Published: February 2008

Titanium isotopic compositions in whole‐rock samples are reported for meteorites from all four carbonaceous chondrite classes. Characteristic isotopic patterns are derived for each class, since meteorites in a given class usually, though not always, give the same pattern. No anomalies are resolved at the 47/46 and 48/46 ratios, but small 50 excesses are prevalent [ε(50/46) mean values are CI=+1.0±0.8; CM=+2.4±0.6; CO=+3.0±0.5; CV=+3.3±0.5]. Among the three classes where Ti anomalies are clearly present, the mean values for the 50 excesses are the same within the uncertainties. In contrast, the CI class gives just a hint of a 50 excess. Available data, including analyses of Murchison (CM) density separates, suggest that anomalous Ti is not confined to phases in refractory inclusions. Kakangari, a petrologically and chemically peculiar meteorite, shows a clear deficit of 50, thereby supporting a previous suggestion that it is a unique carbonaceous chondrite.
Lidar measurements of gravity wave saturation effects in the sodium layer
Authors: Gardner C. S. , Voelz D. G.
Published: February 2008

The linear theory of internal gravity waves predicts an exponential growth of the velocity amplitudes with altitude. At high enough altitudes, the wave amplitudes become so large that nonlinear effects and turbulent breakdown prevent the velocities from increasing further with height. When this happens, the wave is said to be saturated. In this paper, it is shown that the wave amplitude and amplitude growth factor can be accurately computed from measurements of the sodium layer spatial power spectrum. Lidar measurements are presented which show gravity wave growth lengths that are nearly twice the unsaturated value of 12 km.
On the dissolved surface oxygen supersaturation in the Arctic
Authors: Top Zafer , Martin Seelye , Becker Paul
Published: February 2008

Recently we reported anomalous dissolved neon‐helium ratios in the Arctic Ocean and suggested that the neon supersaturation is caused by the freezing process. We also predicted supersaturation of dissolved gases such as oxygen, which are heavier than neon. To pursue the tracer potential of these gases, we recently collected more seawater samples for the measurements of the noble gases, made dissolved oxygen measurements, and performed a set of laboratory freezing experiments. Here, we report the results of dissolved oxygen measurements made during the laboratory freezing experiments, and during the MIZEX 84 field program. In the laboratory we found that 1cm of ice growth caused approximately 0.5% dissolved oxygen supersaturation in a 90cm deep water column. Conversely, the ice phase was 53±2% undersaturated in dissolved oxygen, a result which is, within experimental uncertainties, identical to that obtained in the field.
Synthetic seismograms for a complex crustal model
Authors: Sandmeier K.‐J. , Wenzel F.
Published: February 2008

The algorithm of the original Reflectivity Method has been vectorized and implemented on a CDC CYBER 205 computer. Calculation times are shortened by a factor of 20 to 30 compared with a general purpose computer with a capacity of several million floating point operations per second (MFLOP). The rapid calculation of synthetic seismograms for complex models, high frequency sources and all offset ranges is a provision for modeling not only particular phases but the whole observed wavefield. As an example we model refraction data of the Black Forest, Southwest Germany and are able to derive rather tight constraints on the physical properties of the lower crust.
Minimum detectable pollution levels from satellite imagery
Authors: Tsonis A. A. , Leaitch W. R.
Published: February 2008

In this paper the detection of haze using satellite imagery is compared with simultaneous aircraft measurements of haze parameters. The vertical optical depths of the effective pollutant layers are compared with results from the satellite data in order to gauge a threshold for the detection of haze from satellites. This comparison indicates that in terms of the optical depth this threshold is approximately equal to 0.065. Regression analysis indicates that a ground aerosol SO4= concentration of ∼3 µgm−3 may be typical of such a value of optical depth.
Velocity shears and sub‐km scale irregularities in the nighttime auroral F‐region
Authors: Basu Sunanda , Basu Santimay , Senior C. , Weimer D. , Nielsen E. , Fougere P. F.
Published: February 2008

Preliminary results are presented on the nature of a distinct class of sub‐km high latitude irregularities which can create localized regions of near saturated VHF and fairly intense UHF scintillations in the nighttime auroral F‐region. The unique feature of this class of irregularities is that it is associated not with large scale (several tens of km) organized density gradients in the F‐region but with velocity shears with shear gradient scale lengths ∼10km. The presence of velocity shears was established by EISCAT ion drift measurements, continuous STARE measurements of electron drift and the in‐situ ion drift measurements from the HILAT satellite. Analytical and numerical simulation studies of velocity shear driven Kelvin‐Helmholtz type plasma instabilities are necessary to elucidate the generation mechanism of this class of irregularities.
Effect of nonprecipitating clouds on the aerosol size distribution in the marine boundary layer
Authors: Hoppel W. A. , Frick G. M. , Larson R. E.
Published: February 2008

The size distribution of particles smaller than 0.5 µm has been measured over the tropical Atlantic and Pacific oceans with a differential mobility analyzer. In regions remote from continental influences the size distribution generally has peaks at about .02‐.03 µm and at .08‐.15 µm with a minimum in the .05‐.08 µm radius range. The data provides strong evidence that nonprecipitating clouds play an important role in transferring material from the gas phase and from smaller particles into the 0.08 to .15 µm radius range, and that they are responsible for the doubly peaked size distributions frequently observed over the oceans.
Implications of the Stagnation Line Model for energy input through the dayside magnetopause
Authors: Pudovkin Mikhail I. , Semenov Vladimir S. , Heyn Martin F. , Biernat Helfried K.
Published: February 2008

Based on the formation of a stagnation line at the magnetopause the electromagnetic energy transport from the solar wind into the dayside magnetosphere is analyzed. The resulting energy flux is proportional to v∞B∞² sin² (θ∞ ‐ ϕ∞), where v∞ and B∞ are the solar wind speed and magnetic field and θ∞ ‐ ϕ∞ is the angle between the IMF and the stagnation line projected into the interplanetary space. A stagnation line parallel to the separator gives approximately the sin4(θ∞/2) energy flux dependence of Akasofu's ε‐index.
An apparent double‐planed Benioff Zone beneath northern Chile resulting from misidentification of reflected phases
Authors: Cahill Thomas , Isacks Bryan L.
Published: February 2008

Epicenters of intermediate‐depth events located by the ISC, taken together with focal depths determined from the reflected phase pP, define a double‐planed seismic zone beneath northern Chile and northwestern Argentina. The lower zone of seismicity, however, is the result of a systematic misidentification of sP as pP at many North American seismograph stations. The lower seismic plane consists of 14 earthquakes located between 22° and 24.5° S that occurred between 1964 and 1984. Depths calculated from pP arrival times reported to the ISC are heavily biased by the abundance of reports from high‐gain stations in western North America. Reports from these stations place the lower zone events at 125‐150 km depth, 35‐45 km below the main Wadati‐Benioff zone. Short‐period seismograms produced by the lower zone earthquakes at North American stations show only one clear reflected phase following P, which is often incorrectly identified as pP. Our identification of this phase as sP results in a shallower depth determination that is in agreement with pP and sP arrival time reports from stations in Africa and Southern Europe. The absence of a strong pP phase from North American records for the 14 events can be explained by the proximity of its take‐off angle to a nodal plane on the focal sphere. The majority of intermediate depth events in the region lie in the upper plane; these earthquakes do produce recognizable pP phases. Hence, no clear evidence exists for a double‐planed seismic zone in this region.
Global reorientation and its effect on tectonic patterns on Ganymede
Authors: Murchie Scott L. , Head James W.
Published: February 2008

The perturbation to the momental figure of Ganymede by the impact basin Gilgamesh was modelled, and it was found that the formation of the basin could have significantly reoriented the satellite. Global trends of groove orientation suggest that groove sets formed in reactivated zones of weakness, which were created by tidal despinning and furrow formation. The paleopole on which despinning occurred was shifted about 15° after the emplacement of most grooved terrain. The youngest grooves have orientations consistent with those expected for fractures caused by the reorientation.
Preliminary measurements of SO2 adsorbed on ice
Authors: Sommerfeld R. A. , Lamb D.
Published: February 2008

Three adsorption isotherms of SO2 on ice were measured at −3°, −11°, and −30°C in the SO2 concentration range of 0.3 to 6 ppmV. The isotherms indicated that there is a strong increase of adsorption as the temperature rises toward the melting point. This behavior may correlate with the presence of a "quasi‐liquid" layer on the surface of ice. If this behaviour is typical of impurity adsorption on ice, it is important in the processes that govern the acquisition, transport and storage of atmospheric pollutants by snow.
Large plasmaspheric electric fields at L ∼ 2 measured by the S3‐3 satellite during strong geomagnetic activity
Authors: Gonzalez W. D. , Pinto O. , Mendes O. , Mozer F. S.
Published: February 2008

Large plasmaspheric electric fields at L ∼ 2 measured by the S3‐3 satellite during strong geomagnetic activity are reported in this letter. Since these measurements have amplitudes comparable to those of the local corotation electric field, during such events the plasmasphere is expected to get strongly altered even at such low L‐values. Furthermore, those measurements could contribute to the understanding of the physics of the convection‐electric field penetration to the low latitude plasmasphere as well as of the “disturbed” dynamo, during strong geomagnetic activity. For this purpose, critical parameters related to geomagnetic activity are also presented for the reported electric field events.
Electron acoustic instabilities in the geomagnetic tail
Authors: Ashour‐Abdalla Maha , Okuda Hideo
Published: February 2008

Electron acoustic waves present in a two temperature electron plasma can be driven unstable when ion beams propagate along the magnetic field. Both linear theory and numerical simulations indicate that this instability contributes to the generation of broadband electrostatic noise (BEN) in the geomagnetic tail.
Three dimensional energetic ion bulk flows at comet P/Giacobini‐Zinner
Authors: Richardson I. G. , Cowley S. W. H. , Hynds R. J. , Sanderson T. R. , Wenzel K‐P. , Daly P. W.
Published: February 2008

Using energetic ion data obtained by the EPAS experiment on the ICE spacecraft we investigate the three dimensional ion bulk flow in the mass loading region around the comet P/Giacobini‐Zinner. We find relatively abrupt changes in flow speed (∼ 100 km s−1) at the boundaries between the pickup and mass loading regions. Flow deflections away from the comet tail of ∼15° are observed at the boundaries with peaks upto ∼30° inside the mass loading region. Ion energies of ∼300 keV are found inside the mass loading region which suggest the need to consider other ion acceleration mechanisms in addition to solar wind pickup.
Mesospheric ozone changes associated with 27 day solar ultraviolet flux variations
Authors: Aikin A. C. , Smith H. J. P.
Published: February 2008

Solar ultraviolet flux changes associated with the 27‐day solar rotational period cause corresponding variations in mesospheric ozone near the maximum of the 11‐year sunspot cycle. This statement is based on a correlation and spectral analysis of ozone mixing ratios, deduced from Solar Mesospheric Explorer satellite‐based measurements of 1.27‐µm O2 airglow emission and solar flux observations made from the same spacecraft in 1982. With the Lyman α flux taken as an indicator of solar ultraviolet variability, spectral analysis shows a primary period of 27.1 days with a secondary period of 13.5 days. The 27.1‐ day period is observed in the ozone mixing ratio data together with other periods, including 13.5 days. Both a classical statistical analysis and a time series treatment show that for 244 days there is a correlation between ozone and solar flux near 50 km and between 65 and 70 km. Calculations predict a positive correlation over the entire mesosphere if there is no change in temperature accompanying the solar flux. Lack of correlation is temperature induced.
The observation of HF‐enhanced plasma waves with the EISCAT/UHF‐radar in the presence of strong Landau‐damping
Authors: Frey A.
Published: February 2008

It is well known that intense HF‐radiowaves of the ordinary mode transmitted from the ground enhance plasma waves near the reflection height in the ionosphere. These enhancements are observed as an increase in the returned power of radars having a wavevector equal to one half the wavevector of the enhanced plasma waves. It is expected that strong Landau‐damping will suppress such enhancements if kλD ≃ 0.25 ( k and λD correspond to the wavevector of the Langmuir wave and the Debye‐length) which was the case for Langmuir‐waves detected by the EISCAT/UHF radar during a recent HF‐modification experiment at Tromsø. Enhanced plasma waves were observed unexpectedly at a low heater frequency of fHF = 2.76 MHz. Enhancements at this frequency were not observed during previous attempts and were believed to be damped too strongly to be observable. The observed power threshold can marginally be matched with theory under the assumption of low but not unreal electron and ion temperatures. The observed spectra indicate that the interaction is more intricate than expected under the given conditions.
The major boundary faults in eastern Long Valley Caldera; magnetotelluric and gravity constraints
Authors: Hermance John F. , Karlsdottir Ragna
Published: February 2008

Geophysical studies of the major boundary fault(s) in eastern Long Valley caldera have led to significantly different models being proposed for the subsurface structure of this area. Pakiser originally interpreted gravity data to propose a steep vertical offset across the eastern boundary fault(s) which may be as great as 5 km. On the other hand, Hill employing seismic refraction data, and Abers, who reinterpreted the available gravity data in the light of the "hard" seismic constraints of Hill, suggested that the offset across this fault may be much more gentle. However, new magnetotelluric data may call for a revision of these models. Based on these recent MT results, offsets along the eastern boundary fault appear to be somewhat steeper than recent models would suggest. Our current thinking would favor a model more in keeping with the one originally envisaged by Pakiser, but with less throw (approximately 2 km) across the faults.
Comparison of GEOS‐3 and SEASAT Altimeter Resolution Capabilities
Authors: Marks Karen M. , Sailor Richard V.
Published: February 2008

A comparison is made between GEOS‐3 and SEASAT altimeter data with regard to noise power spectral density (PSD), derived geoid PSD, and short wavelength resolution. At wavelengths greater than 450 km the noise PSDs for GEOS‐3 and SEASAT are essentially the same and are attributed to mesoscale oceanographic effects. At shorter wavelengths the noise spectra diverge because of the higher GEOS‐3 instrument noise. The average along‐track geoid PSDs are nearly identical between wavelengths of 4500 and 72 km. The spectral coherence between repeat tracks shows that the short wavelength resolution of SEASAT data is ≈32 km, and for GEOS‐3 it is ≈60 km.
The Nazca‐South America convergence rate and the recurrence of the Great 1960 Chilean Earthquake
Authors: Stein Seth , Engeln Joseph F. , DeMets Charles , Gordon Richard G. , Woods Dale , Lundgren Paul , Argus Don , Stein Carol , Wiens Douglas A.
Published: February 2008

The seismic slip rate along the Chile Trench estimated from the slip in the great 1960 earthquake and the recurrence history of major earthquakes has been interpreted as consistent with the subduction rate of the Nazca plate beneath South America. The convergence rate, estimated from global relative plate motion models, depends significantly on closure of the Nazca ‐ Antarctica ‐ South America circuit. NUVEL‐1, a new plate motion model which incorporates recently determined spreading rates on the Chile Rise, shows that the average convergence rate over the last three million years is slower than previously estimated. If this time‐averaged convergence rate provides an appropriate upper bound for the seismic slip rate, either the characteristic Chilean subduction earthquake is smaller than the 1960 event, the average recurrence interval is greater than observed in the last 400 years, or both. These observations bear out the nonuniformity of plate motions on various time scales, the variability in characteristic subduction zone earthquake size, and the limitations of recurrence time estimates.
Magnetic resonance imaging analyses of varved marine sedimentary records of the Gulf of California
Authors: Briskin Madeleine , Robins Jon , Riedel William R. , Booker Ron
Published: February 2008

Nuclear Magnetic Resonance Imaging used for the first time to analyze marine sedimentary records of the Gulf of California is a remarkable improvement over the more conventional X‐ray technique in the identification of organic rich layers. Analytical results indicate that NMRI differentiates clearly between organic rich (light) and organic poor (dark) deposits. It also provides a fine resolution of sedimentary structures, laminae and stratigraphic subtleties. It may be made to yield a three‐dimensional stratigraphy; the procedure is nondestructive. The organic vs. inorganic resolution provided by NMRI technology complemented by X‐ray when needed should facilitate future studies of paleoceanographic, paleoclimatic and biogeochemical cycles recorded in the vast deposits of marine clays.
In‐situ observations of cometary pick‐up iIons ≥0.2 AU upstream of comet Halley: ICE observations
Authors: Wenzel K.‐P. , Sanderson T. R. , Richardson I. G. , Cowley S. W. H. , Hynds R. J. , Bame S. J. , Zwickl R. D. , Smith E. J. , Tsurutani B. T.
Published: February 2008

Burst‐like enhancements of energetic ions were observed by the EPAS instrument on the International Cometary Explorer (ICE) during its closest approach to (28 × 106 km upstream of) Comet P/Halley, in late March 1986. The enhancements showed considerable temporal structure and highly anisotropic angular distributions, with strong ion streaming in the antisolar direction. The ion intensity was modulated by the varying solar wind speed (the latter reaching maxima of around 600 km s−1), as was found to be the case for heavy cometary ions accelerated by pick‐up in the solar wind flow, during the ICE encounter with Comet P/Giacobini‐Zinner (G‐Z). We therefore conclude that we observed pick‐up ions (most probably ≥ 65 keV oxygen ions) produced by heavy neutrals from Comet Halley. The region of pick‐up ions extended to more than 0.2 AU (∼35 × 106 km) from the nucleus at this time, at least three times further than was observed during the Giotto and VEGA encounters. The observations of energetic ions at such large distances suggest the presence, in the neutral atmosphere surrounding the nucleus, of a component with an ionisation scale length of 5‐10 million km, resulting from a relatively high expansion speed of a few km s−1 and/or an ionisation time scale of a few times 106s.
The thermoluminescence sensitivity ‐ Metamorphism relationship in ordinary chondrites: Experimental data on the mechanism and implications for terrestrial systems
Authors: Guimon R. Kyle , Sears Derek W. G. , Lofgren Gary E.
Published: February 2008

Hydrothermal annealing experiments have been performed on samples of the Sharps meteorite in order to investigate the mechanism responsible for the metamorphism‐related, 105‐fold range in the thermoluminescence (TL) sensitivity in ordinary chondrites. Duplicate 50 mg samples of meteorite were annealed under the following conditions: (a) 168 h at 785°C and 1 kbar; (b) the same time, temperature and pressure, but with 2 wt% water; (c) 174 h at 855°C and 0.77 kbar with 2 wt% water and 2 molal sodium disilicate (NadiSi); (d) the same time, temperature and pressure as the preceding samples, but with 10 wt% H2O and 2 molal NadiSi. Samples annealed under the first three sets of conditions showed little or no change in their TL sensitivities, however the samples annealed with 10 wt% water and 2 molal NadiSi showed a 3 to 10‐fold increase in TL sensitivity, and the temperature of the TL peak was suggestive of feldspar in the high‐temperature form. We suggest that these data are consistent with the TL sensitivity‐metamorphism relationship in ordinary chondrites being due to the formation of the TL phosphor, feldspar, by the crystallization of chondrule glass.
New paleomagnetic data from Oligocene formations of northern Aegea
Authors: Kissel C. , Kondopoulou D. , Laj C. , Papadopoulos P.
Published: February 2008

New paleomagnetic data obtained from volcanic and plutonic formations in Thrace (Northern Aegea) show that this region has not undergone any significant rotation since the Lower Oligocene. The mean value of the inclination is shallower than expected on the basis of a geocentered dipole field implying a large northward drift of about 1000 km. Although a comparison with published data from Bulgaria leads to a puzzling large shortening between these two regions, the measured shallow inclinations are coherent with most of other paleomagnetic studies from Oligocene formations throughout the entire Mediterranean area. Together with published results from Chalkidiki Peninsula, our data suggest that the ‘Circum Rhodopean Belt’ was almost rectilinear and trending E‐W in Lower Oligocene time.
Similarity analysis of the Martian polar caps
Authors: Philip J. R.
Published: February 2008

The similarity hypothesis is that the seasonal pattern of deviation from mean CO2 mass in each cap is of the same shape, with an intercap phase difference of half a Martian year. We thereby decompose the annual pressure variation into separate components of CO2 exchange with each cap. Sublimation at one cap and condensation at the other tend to occur simultaneously. The annual fluctuation of CO2 mass in the two caps thus greatly exceeds previous estimates based on treating each cap in isolation. Inferred behavior is generally consistent with optical data on cap recession. The seasonal pattern of meridional mass flux of CO2 is estimated.
On the role of surface tension in the migration of melts and fluids
Authors: Stevenson D. J.
Published: February 2008

It is shown that surface tension can cause redistribution of melt in a partially molten medium, in accordance with a non‐linear diffusion equation for the melt fraction. The associated diffusivity D depends on the surface energy and is positive (stable) for dihedral angle <60° and negative (unstable) for dihedral angle >60°. In the more likely stable case, D ∼ 10−7 cm² .s−1 is typical for mantle melts, but a value as high as 10−1 cm² .s−1 is conceivable for volatile‐rich fluids. Surface tension may play an important role in creating pathways for meta‐somatizing fluids in the Earth, but does not appear likely to affect substantially the existing estimates of large scale melt migration (e.g., beneath mid‐ocean ridges).
A computation of stratospheric heating rates and the diabatic circulation for the Antarctic spring
Authors: Rosenfield Joan E. , Schoeberl Mark R.
Published: February 2008

A radiative transfer model is used to compute the net heating and diabatic circulation from observed temperature and ozone data in the Southern Hemisphere during September and October of 1979, 1980, and 1984. There is an increase in net heating near the pole from September to October, which is associated with an upward cell in the diabatic circulation. This is consistent with dynamical theories of the observed intraseasonal changes in total ozone which postulate the development of an upward circulation at the pole. However, estimates of the mass circulation at the pole suggest that an additional heat source of at least 0.5 K/day is required to maintain the upward cell. Increased net heating at the pole from 1979 to 1980 and decreased net cooling at mid to subpolar latitudes from 1979 to 1984 is also found, which suggests a trend toward increased upward circulation at the poles and downward motion at mid‐latitudes consistent with the observed changes in total ozone.
Comments on the theory of absolute and convective instabilities
Authors: Oscarsson Tord E. , Rönnmark Kjell G.
Published: February 2008

The theory of absolute and convective instabilities is discussed and we argue that the basis of the theory is questionable, since it describes the linear development of instabilities by their behaviour in the time asymptotic limit. In order to make sensible predictions on the linear development of instabilities, the problem should be studied on the finite time scale implied by the linear approximation.
The heights of polar mesospheric clouds
Authors: Thomas Gary E. , Olivero John J.
Published: February 2008

Data from the Solar Mesosphere Explorer satellite of polar mesospheric clouds have been used in determining the variation of cloud height from 1981 to 1985. Applying various corrections to the apparent tangent heights measured at the atmospheric limb, we find no significant variation of height within an individual cloud season (−10 days to + 50 days relative to summer solstice) either with latitude or local time. Furthermore, no significant year‐to‐year variation is found over the 4‐year time span. We find significantly higher (2 km) PMC cloud heights in the north than in the south. The average value of 85.0 ± 1.5 km for the northern PMC is in good agreement with measurements from the OGO‐6 satellite, rocket‐borne photometers and ground‐based triangulation of noctilucent clouds.
An explanation for apparent time delays in phase‐reversed Rayleigh waves from underground nuclear explosions
Authors: Day Steven M. , Stevens Jeffry L.
Published: February 2008

Rayleigh waves from underground nuclear explosions which are accompanied by high levels of tectonic strain release are observed to be reversed and time delayed relative to Rayleigh waves from “normal” underground explosions. The “time delays” can be explained as an interference effect between the explosion and tectonic source time functions which magnifies the true phase difference between the source functions. The phase of the explosion source time function is advanced relative to the phase of the tectonic source function, and the magnitude of the time advance is directly related to the amount of overshoot in the explosion source time function. The phase distortion is more complex than a simple time delay, and may appear as a constant phase shift with no linear trend. Apparent time advances are also possible; however because of small differences between the excitation functions of the explosion and tectonic sources at shallow depths, the phase shift will appear more frequently as an apparent time delay. Observations of Rayleigh wave phase shifts from underground explosions at the Soviet East Kazakh test site recorded at SRO stations are in very good agreement with simulated phase shifts derived from synthetic calculations.
Few 2‐50 km corrugations on the core‐mantle boundary
Authors: Menke William
Published: February 2008

Short‐period PcP amplitudes have been observed to vary by a factor of about 20 in the epicentral range 40‐85°. This behavior is due to the reflection coefficient at the core‐mantle boundary, which varies from a maximum of about 0.5 at an angle of incidence of about 65° to zero at an angle of incidence of about 85° (corresponding to an epicentral ranges of about 60‐90°). We present physical model experiments in which we study the effect of corrugations of the core‐mantle boundary on PcP amplitudes. We find that corrugations with 2‐50 km scale lengths would radically alter the amplitude‐range behavior of short‐period PcP, reducing its variation with range. The observed pattern of short‐period PcP amplitudes indicates that the core‐mantle boundary is smooth on these scales, with amplitudes less than a few hundred meters.
Anisotropy of the inner core inferred from PKIKP travel times
Authors: Morelli Andrea , Dziewonski Adam M. , Woodhouse John H.
Published: February 2008

Travel‐time residuals of the PKIKP phase observed between 170° and 180° show an axisymmetric pattern of degree 2 with an amplitude of about 2 seconds. The effect at shorter distances is much less pronounced and the entire data set cannot be explained by a physically realistic radial distribution of (isotropic) heterogeneity. We propose that, in addition to the general (isotropic) heterogeneity, the inner core is anisotropic with cylindrical symmetry aligned with the earth's rotation axis. Average P‐velocity along this axis is about 1 percent faster than in the equatorial plane.
A new model for the ion beams in the plasma sheet boundary layer
Authors: Whelan T. , Goertz C. K.
Published: February 2008

A new model is proposed for the ion beams frequently observed in the plasma sheet boundary layer. The model assumes injection of magnetosheath plasma onto closed tail field lines. The plasma then expands along the field lines and is convected towards the earth. Particle simulations of the Expansion process are used to calculate properties of these beams. The expansion produces beams of ions at energies of up to a few tens of kBTe, which are consistent with the observed energies of the beams.
Diurnal variation of the OH concentration in ambient air
Authors: Shirinzadeh B. , Wang Charles C. , Deng D. Q.
Published: February 2008

OH concentrations in ambient air outside Ford Laboratory were measured in the months of July and August 1986 using the fluorescence technique at low pressures. The peak OH concentration was observed to be about 3 × 106 molecules/cm³; the daytime average OH concentration was found to be in the range of middle 105 molecules/cm³, and the nighttime average below the detection limit of 0.9 × 105 molecules/cm³. It is demonstrated that use of moving average may create the appearance of oscillatory behavior in the diurnal variations of the deduced OH concentration.