bluuebunny/crossref_metadata_2025 huggingface dataset:
Measurements of the stratospheric carbon dioxide concentration over Japan using a Balloon‐borne cryogenic sampler
Authors: Nakazawa T. , Machida T. , Sugawara S. , Murayama S. , Morimoto S. , Hashida G. , Honda H. , Itoh T.
Published: February 2004

Stratospheric air samples have been collected once per year since 1985 over Japan using a balloon‐borne cryogenic sampler and then analyzed for their CO2 concentrations. The measurements showed high values of CO2 in the lowest part of the stratosphere, then a decrease with height to 20.0–25.0 km, and almost constant values above this level. From the comparison with the results of our aircraft measurements in the upper troposphere and lower stratosphere, it is suggested that the vertical profile of stratospheric CO2 over Japan is strongly related to transport processes that are associated with tropospheric air being introduced into the stratosphere in the tropical region and then moving poleward with different speeds at different heights. The average rate of the CO2 increase from 1985 to 1991 was estimated to be 1.4 ppmv/year; this is similar to the rate found for the troposphere over the same period.
Sulfur chemistry in the wake of comet Shoemaker‐Levy 9
Authors: Zahnle Kevin , Mac Low Mordecai‐Mark , Lodders Katharina , Fegley Bruce
Published: February 2004

A curious and unexpected result of the impact of P/Shoemaker Levy 9 with Jupiter was the production of enormous amounts of molecular sulfur (S2). Here we show that S2 is the natural product of disequilibrium chemistry at low pressures in shocked jovian air, its formation a byproduct of hydrogen recombination. The species observed by the HST — S2, CS2, and H2S — imply that the G fragment penetrated the NH4SH cloud but did not reach the water table. A typical impact within or below the NH4SH clouds produces about 0.03–0.1 impactor masses of S2. Because comets are relatively hydrogen‐poor, SO2, not S2, is the major product of shocking a water‐rich comet, while S2, CS2, and OCS are major products of a dessicated comet. In all cases we find that as the gas cools S2 converts to the stable low temperature allotrope S8, although other chemical fates not modeled here might intervene first.
Foreshocks and pre‐events associated with the nucleation of large earthquakes
Authors: Shibazaki Bunichiro , Matsu'ura Mitsuhiro
Published: February 2004

We propose a theoretical model which can explain the occurrence of foreshocks and pre‐events associated with the nucleation of large earthquakes. We consider a broad weak zone with a locally strong part (asperity) on a fault plane in a two‐dimensional framework and examine the transition process from quasistatic nucleation to high‐speed rupture propagation through numerical simulations. The dynamic rupture of the asperity occurs in three different manners, as aseismic slip, foreshock or pre‐event, depending on the peak stress of the asperity. In all cases the rupture of the asperity accelerates the nucleation of main rupture.
Observation of pressure change associated with hydrothermal upwelling at a seamount in the South Mariana Trough using an ocean bottom seismometer
Authors: Sato Toshinori , Kasahara Junzo , Fujioka Kantaro
Published: February 2004

An OBSH (ocean bottom seismometer with hydrophone) was deployed just 1 m from a hot thermal vent on the summit region of a seamount located 18 km east of the south Mariana Trough axis to record continuous data on hydrothermal activity. Although the seismicity beneath the seamount was very weak, numerous pulse shape (pressure) events showing sudden pressure decrease were observed on the hydrophone channel. The characteristic period of the pressure events varied from 20 seconds to 1 minute. After the submersible Shinkai 6500 relocated the OBSH 10 m south of the vent, where no thermal vents existed, the number and amplitude of pressure events drastically decreased. This suggests that pressure events were generated by the hot water upwelling from the thermal vent. The pressure events appear to be related to the ocean tide. This experiment indicates that observations using OBSHs are an effective means of monitoring hydrothermal activity.
Aftershock distribution of the October 4, 1994 Mw8.3 Kurile Islands Earthquake determined by a local seismic network in Hokkaido, Japan
Authors: Katsumata K. , Ichiyanagi M. , Miwa M. , Kasahara M. , Miyamachi H.
Published: February 2004

On October 4, 1994, an earthquake with magnitude Mw8.3 occurred in the western part of Kurile Islands at 43.42°N, 146.81°E and 33 km in depth. The hypocenter parameters were determined by Hokkaido University in Japan. Aftershocks following this remarkable event were located using data from a local seismic network operated by Hokkaido University. We found that most of the aftershocks occurred (1) on the fault plane of the mainshock, (2) in the subducting plate around the fault plane of the mainshock, and (3) in the focal area of the largest aftershock, which occurred on October 9 with Mw7.3. Both (2) and (3) were not active immediately after the mainshock. Considering the time sequence of the aftershock activity, we identified one of the nodal planes of the Harvard quick CMT solutions as the fault plane of the mainshock; the strike is almost parallel to the trench axis and the dip angle is near vertical. It is obvious that this event is different from a low‐angle thrust‐type interplate earthquake. The distribution of aftershocks strongly suggests that it is an intraplate event.
On the utility of the molecular oxygen dayglow emissions as proxies for middle atmospheric ozone
Authors: Mlynczak Martin G. , Olander Daphne S.
Published: February 2004

The molecular oxygen dayglow emissions, O2(a1Δg → X3Σg) at 1.27 µm and O2(b1Σg → X3Σg) at 762 nm, arise in part from processes related to the Hartley band photolysis of ozone. It is therefore possible to derive daytime ozone concentrations from measurements of the volume emission rate of either dayglow. The accuracy to which the ozone concentration can be inferred depends on the accuracy to which numerous kinetic and spectroscopic rate constants are known, including rates which describe the excitation of molecular oxygen by processes that are not related to the ozone concentration. We find that several key rate constants must be known to better than 7% accuracy in order to achieve an inferred ozone concentration accurate to 15% from measurements of either dayglow. Currently, accuracies for various parameters typically range from 5% to 100%.
Geographical differences in the UV Measured by intercompared spectroradiometers
Authors: Seckmeyer G. , Mayer B. , Bernhard G. , McKenzie R. L. , Johnston P. V. , Kotkamp M. , Booth C. R. , Lucas T. , Mestechkina T. , Roy C. R. , Gies H. P. , Tomlinson D.
Published: February 2004

Five UV spectroradiometers representative of the types used in monitoring programs on several continents were intercompared at the Fraunhofer Institute for Atmospheric Environmental Research (IFU), Garmisch‐Partenkirchen, Southern Germany, during a campaign in August 1994. Global spectral irradiances between 290 and 410 nm were measured over a range of solar zenith angles from 30° to 80°. Scans were synchronized to enable useful comparisons to be made under changing weather conditions, which included overcast, partly cloudy, and clear skies.

No exchange of data was allowed between participating groups until after the campaign. At wavelengths longer than 310 nm, the spectra generally agreed to within ±5%. At wavelengths shorter than 310 nm, differences between instruments were larger, especially at larger solar zenith angles. Causes of differences are discussed. For all instruments, deviations in erythemally weighted irradiances were always less than 7% from the mean. The agreement between measurement systems is sufficient to allow an investigation of geographical differences in UV, under all observing conditions. UV doses measured at sites in the southern hemisphere are systematically larger than those measured at the corresponding northern latitudes. During the summer months the daily doses at the South Pole exceed those at mid‐latitudes in the Northern Hemisphere. Further investigations must be performed to establish a global UV‐climatology.
A spectroradiometer for the measurement of direct and scattered solar irradiance from on‐board the NASA ER‐2 high‐altitude research aircraft
Authors: McElroy C. T.
Published: February 2004

A compact, diode‐array spectrophotometer has been designed to make measurements of the downward spectral flux on a horizontal surface, the limb brightness and the apparent brightness in the nadir direction from on‐board the NASA ER‐2 research aircraft. The instrument was included as part of the photochemical payload used for the Stratospheric Photochemistry, Aerosol and Dynamics Expedition (SPADE) of the NASA High‐Speed Research Program. The spectrophotometer is based on a 1024‐element, randomly‐addressable Reticon photodiode array and makes measurements covering the 300 to 775 nm spectral region at a resolution of about 1 nm. Some aspects of the design and the performance of the instrument during SPADE will be presented. The direct‐beam, spectral measurements are in good agreement with modelled data (MODTRAN).
Nonlinear vortex structures with diverging electric fields and their relation to the black aurora
Authors: Johnson Jay R. , Chang Tom
Published: February 2004

Large, radially divergent electric fields have been observed by the FREJA satellite and have been associated with black auroral curls. We interpret these structures as two‐dimensional solitary nonlinear plasma waves. In accordance with observation, we suggest that these are slowly propagating vortex structures traveling along elongated density depletions perpendicular to the magnetic field. We demonstrate that these structures are localized in space (the order of 1 km) and can have large, outwardly directed radial electric fields (the order of 1 V/m)—characteristics consistent with FREJA observations.
Evidence of bulk attenuation in the asthenosphere from recordings of the Bolivia Earthquake
Authors: Durek Joseph J. , Ekström Göran
Published: February 2004

Radial modes excited by the 9 June 1994 Bolivia earthquake are analyzed to improve constraints on bulk attenuation in the Earth's interior. Using data recorded at 53 stations, quality factors for six radial modes are determined. The new observations are combined with previously published surface wave and normal mode attenuation measurements, and inverted for radial variations in shear and bulk attenuation, Qμ−1(r) and Qκ−1(r). The consequences of restricting finite Qκ to specific regions of the Earth's interior are investigated using a layered model parameterization. The optimal model is characterized by: 1) no bulk attenuation in the core, 2) a ratio of bulk to shear dissipation in the asthenosphere (∼30%) consistent with the presence of partial melt, and 3) a ratio in the remainder of the mantle (∼1%) consistent with solid‐state mechanisms of attenuation.
Calculation of static deformation following the Bolivia Earthquake by summation of Earth's normal modes
Authors: Ekström Göran
Published: February 2004

The vertical ground displacement associated with the 9 June 1994 great Bolivia earthquake is calculated by summation of Earth's normal modes. Because of the great depth of the earthquake, the contributions to the surface displacement field from modes of low radial and angular orders predominate. Convergence is fast, and the truncated mode sum provides a good estimate of the total global displacement field. The vertical displacement is calculated to be on the order of 1 cm within a few hundred km of the epicenter, and 1 mm at distances as great as 1500 km. Normal mode seismograms are calculated for a location near the epicenter, and the static offset is seen to occur primarily between the P and S phases, consistent with the effect of a near‐field term. The predicted seismograms are in qualitative agreement with the recently reported observations of seismically recorded static displacements on the BANJO broadband array [Jiao et al., this issue]. The static offset calculated in this study is smaller than the observations and predictions reported by Jiao et al., probably owing to uncertainties in the observations and in their approximate calculations, which are based on dislocation theory in an elastic halfspace.
‘Alfvénic shocks’ and low‐altitude auroral acceleration
Authors: Mishin E. V. , Förster M.
Published: February 2004

Electrostatic shocks (ESs) and small‐scale, field‐aligned currents (FACs) are known to be associated with low‐altitude auroral acceleration. We show that this phenomenon can be consistently described by including the transverse wave‐guide for shear Alfvén waves (TAWG) and the density dip in the Alfvén wave model. The TAWG is the density depletion in a low β plasma at h ≤ 2 RE. Paired, anti‐parallel FACs are found to be its eigenmodes. The ne‐dip in the centre, caused by a steep gradient of the electric field, promotes formation of the strong double layer (SDL). This in turn yields a narrow field‐aligned electron beam at the edge of an arc or the black aurora, depending upon whether it is the region of the upward or downward Birkeland current, respectively.
Challenging models for flow in unsaturated, fractured rock through exploration of small scale processes
Authors: Glass R. J. , Nicholl M. J. , Tidwell V. C.
Published: February 2004

Fluid flow in unsaturated, fractured rock is studied with respect to applied environmental problems ranging from remediation of existing contaminated sites to evaluation of potential sites for isolation of hazardous or radioactive wastes. Spatial scales for such problems vary from meters to kilometers with temporal scales from months to tens of thousands of years. Because such scales often preclude direct physical exploration of system response and detailed site characterization, we are regularly forced to use our understanding (or misunderstanding) of the underlying physical processes to predict large scale behavior. It is essential that conceptual models used as the basis for prediction be firmly grounded in physical reality. In this paper, we provide examples of how recent advances in understanding of small‐scale processes within discrete fractures may influence the behavior of fluid flow in fracture networks and ensembles of matrix blocks sufficiently to impact the formulation of intermediate‐scale effective media properties. We also explore, by means of a thought experiment, how these same small‐scale processes could couple to produce a large‐scale system response inconsistent with current conceptual models of flow through unsaturated, fractured rock.
Quantitative visualization of entrapped phase dissolution within a horizontal flowing fracture
Authors: Glass R. J. , Nicholl M. J.
Published: February 2004

An experiment was conducted to demonstrate the utility of quantitative fracture flow visualization techniques in the study of entrapped fluid phase (air) dissolution into a flowing phase (water) within a horizontal, transparent, analog rough‐walled fracture. The fracture aperture field and phase occupancy were measured using light transmission techniques and then combined to calculate bulk water‐phase saturation within the fracture as a function of time. Fracture relative permeability as a function of water‐phase saturation showed a smooth power law behavior during dissolution. Periodic step pulses of clear water within the dyed water inflow yielded dye concentration fields that demonstrate channeling induced by the entrapped air phase. Clusters of the entrapped air‐phase exhibited three types of dissolution behavior: general shrinkage, interfacial recession along cluster appendages, and cluster splitting. Locations for the advance of the wetting phase (water) into a nonwetting entrapped air cluster on its dissolution are not always correlated with either zones of high mass transfer rate (as inferred from gradients in the pulsed dye concentration fields) or with narrow apertures where the wetting phase has been thought to most easily invade. These results suggest that within an individual cluster of the entrapped phase, fluid pressure is at equilibrium and that the path of cluster shrinkage may be controlled primarily by capillary forces resulting from the full three‐dimensional curvature that minimizes surface energy of the phase interface.
Estimation of tail reconnection lines by AKR onsets and plasmoid entries observed with GEOTAIL spacecraft
Authors: Murata Takeshi , Matsumoto Hiroshi , Kojima Hirotsugu , Fujita Atsushi , Nagai Tsugunobu , Yamamoto Tatsundo , Anderson Roger R.
Published: February 2004

We estimate the location of the reconnection line and plasmoid size in the geomagnetic tail using data from the Plasma Wave Instrument onboard the GEOTAIL spacecraft. We first compare AKR onset events with high energy particle observations at geosynchronous orbit. We determine the plasmoid ejection (reconnection) time by the AKR enhancement only when it corresponds to energetic particle enhancement within five minutes. The traveling time of the plasmoid from the X‐line to the spacecraft is calculated by the difference in time of the AKR onset and that of the plasmoid encounter with GEOTAIL. Assuming the plasmoid propagates with the Alfvén velocity in the tail lobe as MHD simulations predict, we estimate the location of the reconnection line in 11 events. The results show that the most probable location of the plasmoid edge is distributed around x = −60 RE in the GSE coordinates. The estimated size of the plasmoids ranges from 10 to 50 RE in the x direction. If we apply this result to the alternative plasmoid model in which the evolution of the tearing instability causes the generation of plasmoids, the X‐line should be approximately at x = −35 RE.
Comet Shoemaker‐Levy 9 at Jupiter
Authors: Shoemaker Eugene M.
Published: February 2004

From the 16th to the 22nd of July, 1994, the world was privileged to witness an event that probably recurs less often than once a century. Collision of the brightest nuclei of Periodic Comet Shoemaker‐Levy 9 produced enormous dark clouds that were the most dramatic and easily observed features on Jupiter recorded by human visual observation. They were seen by tens of thousands of people through hundreds or thousands of telescopes ranging in aperture from 5 to more than 100 cm. Tens of millions of people participated vicariously in the impact event through viewing on television the magnificent images from the Hubble Space Telescope (HST) and from numerous ground‐based telescopes.
Coseismic crustal deformation from the 1994 Hokkaido‐Toho‐Oki Earthquake Monitored by a nationwide continuous GPS array in Japan
Authors: Tsuji Hiromichi , Hatanaka Yuki , Sagiya Takeshi , Hashimoto Manabu
Published: February 2004

Using a brand‐new nationwide continuous GPS array, we monitored coseismic displacements from the October 4, 1994 Hokkaido‐Toho‐Oki (Kurile islands) earthquake (MJMA=8.1). Based on 2‐week time series of site coordinates of 21 GPS stations, we present a coseismic deformation field of whole Hokkaido within 1 cm precision. For example, the station at Nemuro, 170 km west of the epicenter, moved 44 cm to the east and subsided 10 cm. Even stations in southern Hokkaido, 600 km apart from the epicenter, moved a few cm horizontally toward the epicenter. We compare the GPS result with displacements calculated from two preliminary models, assuming fault planes parallel or perpendicular to the Kurile trench. Since the observed were far‐field displacements on land, both models can explain the GPS result.
An analytic expression for the composition of aqueous HNO3‐H2SO4 stratospheric aerosols including gas phase removal of HNO3
Authors: Carslaw Kenneth S. , Luo Beiping , Peter Thomas
Published: February 2004

An analytic expression is given for the composition and volume of stratospheric HNO3‐H2SO4‐H2O aerosols in terms of the temperature and total amounts of H2O, HNO3 and H2SO4, taking into account conservation of HNO3. In contrast to previous parameterisations of equilibrium vapour pressures, the present scheme for calculating the aerosol composition does not require an iteration procedure, thus computation times are significantly reduced, making it ideal for inclusion in large‐scale atmospheric models. Calculated compositions are compared with the results of a comprehensive thermodynamic model for all stratospheric conditions and maximum deviations are presented.
Numerical modeling of Shoemaker‐Levy 9 impacts as a framework for interpreting observations
Authors: Boslough Mark B. , Crawford David A. , Trucano Timothy G. , Robinson Allen C.
Published: February 2004

Computational models of the impacts of Comet Shoemaker‐Levy 9 onto Jupiter may provide the best framework by which the observational data can be interpreted. Among the observations that have already been at least partially explained in a way that appears to be consistent with the impact models are: the sources and timings of multiple flashes observed from Earth, the temperatures and durations of the single flashes observed from the Galileo spacecraft, and the asymmetry of the plumes and ejecta patterns observed by the Hubble Space Telescope. Further modeling subsequent to the impacts has shown that (contrary to our pre‐impact expectations) fireball trajectory data do not provide strong constraints on either fragment mass or maximum penetration depth. Instead, it is the cross‐sectional area of the fragment (or swarm of sub‐fragments) at the time of impact that determines the ejection velocity and trajectory of the fireball. The observation of seemingly consistent plume heights, coupled with this computational result, suggests that SL‐9 fragments were loosely‐bound “rubble piles,” possibly with widely varying masses, that in most cases dispersed to about the same diameter (2.0±0.5 km) by the time they reached the Jovian atmosphere. After more data become available and correlated, and more simulations are performed, we expect that fragment size estimates will become more precise.
Simultaneous observations of neutral and ionic magnesium in the thermosphere
Authors: Gardner James A. , Viereck Rodney A. , Murad Edmond , Knecht David J. , Pike C. P. , Broadfoot A. Lyle , Anderson Emmet R.
Published: February 2004

Earth‐limb observations by the GLO instrument aboard space shuttle mission STS‐53 include the first simultaneous resonant‐scattering detection of Mg+ (279.6–280.3 nm) and neutral Mg (285.2 nm) in the thermosphere. Although Mg+ emissions are observed in approximately 45% of GLO scans over a wide geographic and local‐time range, neutral Mg is observed in fewer than 1% of the measurements, and most of these sightings occur on two consecutive orbits in a near‐equatorial patch at local dusk. Neutral Mg is observed at tangent heights between 150 and 230 km, with an instrument‐view‐column density of 0.4–1.4 × 108 cm−2, compared with simultaneous Mg+ values of 1.4–5.8 × 109 cm−2. Calculated in‐cloud densities are [Mg+] ∼250 cm−3 and [Mg] ∼5 cm−3, and the average ratio of [Mg+] to [Mg] in the individual measurements is 34:1.
Iron hydride formed by the reaction of iron, silicate, and water: Implications for the light element of the Earth's core
Authors: Yagi Takehiko , Hishinuma Takahiro
Published: February 2004

In situ high pressure‐temperature X‐ray observations were made on the system of iron, silicate mineral, and water up to 4.9 GPa and 1350°C using a cubic‐anvil high pressure apparatus and synchrotron radiation. Above a pressure of 2.8 GPa at temperatures above 550°C, iron reacts with water to form iron hydride and iron oxide. The chemical composition of the iron hydride formed is estimated to be FeH0.3‐FeH0.4. This result implies that if water was contained together with iron and silicates at sufficient depth within the primordial Earth, iron should have transformed into iron hydride. The density of iron hydride thus formed can explain a large portion of the density deficit of the Earth's core. These results show that hydrogen is likely a component of the Earth's core.
En echelon ruptures during the Great Bolivian Earthquake of 1994
Authors: Chen Wang‐Ping
Published: February 2004

Rupture during this event has two characteristics. First, bursts of major moment release (subevents) have a component of eastward movement from the epicenter. Second, later subevents show northward directivity. These observations lead to a model with four subevents, the latter three being line sources propagating within approximately ±30° of north. This model has en echelon regions of moment release over sub‐horizontal plane(s) and rupture speeds up to 3.5±0.5 km/s within subevents. Moment release over en echelon regions can accommodate high moment release over a limited seismogenic volume within subducted lithosphere. Depending on the exact geometry of the Wadati‐Benioff zone and the precise direction of rupture propagation, lower bounds on the thickness of the seismogenic zone during this event range approximately 10–40 km. While several aspects of the en echelon rupture model dovetail with predictions based on the anticrack model for deep‐focus seismicity, one must also allow for the possibility that the rupture zone extended beyond the expected thickness of metastable olivine wedge.
Near‐infrared imaging of SL9 impacts on Jupiter from Pic‐du‐Midi Observatory
Authors: Colas F. , Tiphène D. , Lecacheux J. , Drossart P. , de Batz B. , Pau S. , Rouan D. , Sèvre F.
Published: February 2004

Observations of SL9 impacts with an infrared camera on the 1 meter telescope at Pic‐du‐Midi has provided images in filters J, H and K, which show the temporal evolution of the impact sites, in particular at an early stage. The light curves of impacts H and L are presented here; they exhibit similar characteristics, with three successive maxima, corresponding to a succession of atmospheric phenomena following an impact.
Self‐consistent kinetic photoelectron effects on the polar wind
Authors: Tam Sunny W. Y. , Yasseen Fareed , Chang Tom , Ganguli Supriya B.
Published: February 2004

Anomalous electron heat fluxes and recent observations of day‐night asymmetries in polar wind features indicate that photoelectrons may affect polar wind dynamics. These anomalous fluxes require a global kinetic description (i.e., mesoscale particle phase space evolution involving microscale interactions); their impact on the polar wind itself requires a self‐consistent description. In this Letter, we discuss results of a self‐consistent hybrid model that explains the dayside observations. This model represents the first global kinetic collisional description for photoelectrons in a self‐consistent classical polar wind picture. In this model, photoelectrons are treated as test particles, ion properties are based on global kinetic collisional calculations, thermal electron features and the ambipolar field are determined by fluid calculations. The model provides the first global steady‐state polar wind solution that is continuous from the subsonic collisional regime at low altitude to the supersonic collisionless regime at high altitude. Also, the results are consistent with experiments in several aspects, such as order of magnitude of the ambipolar electric potential, qualitative features of the ion outflow characteristics, electron anisotropy and upwardly directed electron heat flux on the dayside.
Constraining odd‐degree earth structure with coupled free‐oscillations
Authors: Resovsky Joseph S. , Ritzwoller Michael H.
Published: February 2004

Several pairs of normal mode multiplets sensitive to long‐wavelength mantle structure are potential coupling partners. Geometric selection rules render such coupling the only means by which normal modes sample odd‐degree mantle structure. That overtone coupling can be strong and can significantly impact normal mode spectra is illustrated using synthetic seismograms for a realistic earth model. These observations motivate the generalization of normal mode spectral fitting to permit simultaneous estimation of even‐ and odd‐degree structural constraints. When generalized spectral fitting is applied to a data set of approximately 150 high signal‐to‐noise vertical records, dominated by data from the Northern Bolivian event (6/9/1994), it is found to reduce misfits appreciably for coupled multiplets 1S5–2S4 and 2S5–1S6, to yield odd‐degree constraints generally consistent with recent mantle models, and to improve agreement between estimated and predicted even‐degree constraints.
Direct detection of the current in a magnetotail flux rope
Authors: Frank L. A. , Paterson W. R. , Kokubun S. , Yamamoto T. , Lepping R. P.
Published: February 2004

The field‐aligned current densities in the core of a magnetotail flux rope were directly detected with plasma instrumentation on board the Geotail spacecraft at a downstream distance of about 96 RE (Earth radii). The axis of the flux rope and the core magnetic fields were directed cross‐tail, and the magnitudes of these core magnetic fields were similar to that in the magneto‐tail lobe at these distances. The radius of the core cross‐section was about 0.7 RE, and the total current was 500,000 A. Together with a recently reported, similar measurement with the Galileo spacecraft these direct detections of current greatly strengthen the previous identifications in favor of flux ropes that were solely based on their magnetic signatures. The detection of the flux rope with the Geotail spacecraft occurred during a period of relative magnetic quiescence.
The role of the Gendrin mode of VLF propagation in the generation of magnetospheric emissions
Authors: Helliwell Robert A.
Published: February 2004

Impulsive VLF wave packets and electron beams may be formed in the magnetosphere from the superposition of Gendrin mode components defined by the condition
where θ=wave normal angle measured from the Earth's static magnetic field
,f=frequency of the wave component and fH = electron gyrofrequency. The frequency range of the Gendrin mode spectrum is defined by fL < f < fH/2, where fL = lower hybrid resonance frequency ≈
and fHi = proton gyrofrequency. Since the group ray velocity of all Gendrin components is given by
where fN = plasma frequency, and is aligned with
and since the longitudinal (parallel to
) component of the phase velocity is the same as υG, a Gendrin wave packet will travel in a homogeneous medium without distortion, constituting a kind of soliton. An electron whose parallel velocity υ∥ is close to υG (i.e., near longitudinal resonance) may become trapped by the E∥ of the Gendrin wave packet, giving up energy to the packet as it propagates in a region of decreasing υG, such as a typical field line path approaching the magnetic equator. As the packet grows E∥ increases causing more trapping and accordingly more wave growth, giving rise to an “Impulsive Wave Instability” (IWI). Wave packet growth is limited by wave loss due to drift away from the main packet of previously generated components that no longer satisfy the Gendrin condition. As the packet leaves the equator growth ceases, the packet collapses and the previously trapped electrons become transient electron beams that may themselves trigger more emissions. It is suggested that the impulsive VLF emissions observed by DE1 and other satellites may be caused by the IWI mechanism.
Plate motion and crustal deformation estimated with geodetic data from the Global Positioning System
Authors: Argus Donald F. , Heflin Michael B.
Published: February 2004

We use geodetic data taken over four years with the Global Positioning System (GPS) to estimate (1) motion between six major plates and (2) motion relative to these plates of ten sites in plate boundary zones. The degree of consistency between geodetic velocities and rigid plates requires the (one‐dimensional) standard errors in horizontal velocities to be ∼2 mm/yr. Each of the 15 angular velocities describing motion between plate pairs that we estimate with GPS differs insignificantly from the corresponding angular velocity in global plate motion model NUVEL‐1A, which averages motion over the past 3 m.y. The motion of the Pacific plate relative to both the Eurasian and North American plates is observed to be faster than predicted by NUVEL‐1A, supporting the inference from Very Long Baseline Interferometry (VLBI) that motion of the Pacific plate has sped up over the past few m.y. The Eurasia‐North America pole of rotation is estimated to be north of NUVEL‐1A, consistent with the independent hypothesis that the pole has recently migrated northward across northeast Asia to near the Lena River delta. Victoria, which lies above the main thrust at the Cascadia subduction zone, moves relative to the interior of the overriding plate at 30% of the velocity of the subducting plate, reinforcing the conclusion that the thrust there is locked beneath the continental shelf and slope.
Have wet and dry Precambrian crust largely governed Cenozoic intraplate magmatism from Arabia to East Africa?
Authors: Bonavia Franco F. , Chorowicz Jean , Collet Bernard
Published: February 2004

To explain Cenozoic continental volcanism between Arabia and East Africa, the existing model infers that a plume impinged beneath Ethiopia, between 30 Ma and 20 Ma, and volcanism extruded within a 1000 km radius. Because relative motion of the Afro‐Arabian plate was about northeast in the last 120 Ma, we infer that at 84 Ma a plume, originated from the core‐mantle boundary, impinged beneath Nubia‐Arabia and is now under the Tanzania craton. This plume caused uplift (Afro‐Arabian swell) and magma under‐plating. After Fyfe's idea (1992), the conceptual model proposed herein suggests that, following plume impact, there was in Nubia‐Arabia only intrusion of mafic dykes because the crust was largely unprocessed (wet). At about 50 Ma the plume was under Ethiopia, and coeval volcanism extruded because the crust was highly recycled (dry). In Zaire‐Burundi and Tanzania, volcanism is explained to be coeval with the arrival of the plume because there also the crust is recycled. In Arabia and Yemen‐Ethiopia continental‐flood basalts younger than 30 Ma formed because lithospheric extension along the Red Sea‐Gulf of Aden was the cause of (or the result of) plume(s), probably originated from the upper mantle.
Measurement of heat of fusion of model basalt in the system Diopside‐forsterite‐anorthite
Authors: Kojitani Hiroshi , Akaogi Masaki
Published: February 2004

Compositions of natural olivine tholeiites were simplified in the system CaO‐MgO‐Al2O3‐SiO2, and approximately eutectic composition in the system diopside(Di)‐ forsterite(Fo) ‐ anorthite(An) (Di:Fo:An = 49.0:7.5:43.5 wt%) was chosen as the model basalt composition. High‐temperature drop calorimetry was performed at 1405–1676K for the samples with the model basalt composition consisting of the mixture of synthetic diopside, forsterite and anorthite. The heat of fusion of the model basalt was obtained to be 506±38 J/g from the difference between the heat content of liquid and that of the mineral mixture at 1543K, which was the approximated eutectic temperature. This heat of fusion shows almost zero enthalpy of mixing in this system. Taking account of the pressure, temperature and composition effects on enthalpy, the heat of fusion of 490–560 J/g is estimated for generation of MORB (mid‐ocean ridge basalt) in the upper mantle.
Evidence for static displacements from the June 9, 1994 Deep Bolivian Earthquake
Authors: Jiao Wenjie , Wallace Terry C. , Beck Susan L. , Silver Paul G. , Zandt George
Published: February 2004

The 1994 Bolivian Earthquake (Mw=8.3) was recorded on‐scale by 8 very‐broadband stations deployed approximately 600 km south of the epicenter. When these seismograms are carefully converted to ground displacement, there appears to be a static offset which is on order of 2 cm. We have modeled the waveforms with a synthetic waveform method that contains near‐, intermediate‐ and far‐field terms. Although the synthetics are only calculated for an elastic half‐space, they compare favorably with the observed waveform in terms of shape. However, the theoretical amplitude is 1/2 of the observed static offset, which probably reflects the limitations of a homogeneous half‐space model and/or the instabilities in deconvolution.
A ground based measurement of the anomalous cloud absorption effect
Authors: Evans W. F. J. , Reinhart C. , Puckrin E.
Published: February 2004

Measurements of the solar shortwave flux using equipment based on solar cell sensors and pyranometers have yielded new information concerning the anomalous cloud absorption effect. A comparison of the solar fluxes for clear and overcast skies in January and February, 1995 suggests that the near‐infrared portion of the solar spectrum beyond 1.1 microns is absorbed preferentially by clouds. In addition, by comparing the observed and modelled column transmittances, it appears that the solar radiation beyond 1.1 microns is absorbed at higher transmittances than expected. On the average, the column absorption under heavy clouds was about 50 W/m², up to a maximum of about 75 W/m². An approximate estimate of the cloud radiative forcing (CRF) ratio was made for overcast days, and it was found to vary from 1.4 to 2.0, in general agreement with the CRF ratio reported by Cess et al. [1995]. It has been assumed previously in climate models that clouds scatter about 30% of the incident solar radiation while absorbing only about 4%. However, the maximum anomalous absorption of about 50 W/m² that we have measured is large in comparison to the radiative forcing of 3.3 W/m² that has been attributed to the presence of greenhouse gases since the pre‐industrial period, and may possibly imply that the climate predictions from general circulation models will have to be recomputed.
Mean winds and tidal and planetary wave motions over Hawaii during airborne lidar and observations of Hawaiian Airglow ALOHA‐93
Authors: Isler Joseph R. , Fritts David C.
Published: February 2004

The mean and low‐frequency wave motions in the mesosphere and lower thermosphere from 70 to 98 km were observed with the MF radar on Kauai during the Airborne Lidar and Observations of Hawaiian Airglow ALOHA‐93 measurement campaign. Two‐day mean zonal winds exhibited a transition from a variable structure with altitude at the beginning of October having westward motions near 80 km and eastward motions at upper and lower levels to more uniform eastward winds with altitude at the end of October. Two‐day mean meridional motions were equally variable, with northward motions at all altitudes on October 1, northward motions above ∼80 km and southward motions below throughout much of the campaign, and largely northward motions at the end of October. Zonal and meridional winds exhibited significant oscillations at ∼5 to 30 day periods, indicative of planetary wave activity during this interval. Diurnal tidal amplitudes and phases were likewise variable, with maximum and minimum rms amplitudes of ∼ 35 and 10 ms−1, approximate phase quadrature with meridional leading zonal, amplitude and phase variability on time scales of ∼ 5 to 15 days, and an overall phase advance during October of ∼10 h. Other tidal components and the two‐day wave had rms amplitudes of ∼ 5 to 10 ms−1.
Interdecadal variability of northern hemisphere circulation recorded by Gulf of Mexico corals
Authors: Slowey Niall C. , Crowley Thomas J.
Published: February 2004

The atmospheric circulation of the extratropical Northern Hemisphere displays several preferred patterns of variability, the most prominent being the Pacific/North American (PNA) pattern. Here we show that a decrease of coral growth at the Flower Garden Banks, Gulf of Mexico, coincides with a decrease in winter air temperature due to the late 1950s shift in the PNA pattern. These results suggest that it may be possible to reconstruct the history of change in the PNA pattern during the last several centuries and examine its relationship to the El Niño/Southern Oscillation phenomenon, the Little Ice Age, and other forms of interdecadal climatic variability. Initial application of this approach suggests that the wintertime phase of the PNA pattern was largely positive from the late 1880s to the first decade of the twentieth century.
P‐wave image of the Peninsular Ranges Batholith, southern California
Authors: Magistrale Harold , Sanders Christopher
Published: February 2004

We invert earthquake P‐wave arrival times to image the 3D distribution of P wave velocities in the Mesozoic Peninsular Ranges batholith and nearby areas in southern California. There is a 3% velocity contrast between the eastern and western Peninsular Ranges at 4 and 20 km depth (west side faster) and a 1 to 1.5% velocity contrast across the San Andreas fault zone (south side faster) in the San Bernardino region at 4 to 14 km depth. The San Andreas velocity contrast is due to the juxtaposition of different rock types by slip along the fault zone. The Peninsular Ranges batholith velocity contrast is due to a difference in rock composition across the batholith. The maximum gradient in the crustal velocities is coincident with a compositional boundary within the batholith that reflects emplacement of the batholith across juxtaposed oceanic and continental crust. Quaternary fault development has been in part concentrated at this boundary.
A large statistical study of the entry of interplanetary magnetic field Y‐component into the magnetosphere
Authors: Wing S. , Newell P. T. , Sibeck D. G. , Baker K. B.
Published: February 2004

We used 5 years of GOES‐6 and 6 years of GOES‐7 data to correlate the y‐component of the geosynchronous magnetic field with the y‐component of IMF. One motivation is that the subsolar merging model and the antiparallel model predict distinctly different patterns for By in the magnetosphere as a function of IMF By. Although both models predict that nightside magnetospheric magnetic field will tilt in the direction of the IMF By, the antiparallel merging model predicts that magnetospheric magnetic field lines in the vicinity of local noon will tilt in the direction of the IMF, where as the subsolar model does not. The correlation coefficients between the geosynchronous data and the IMF By peak at both noon (0.61) and midnight (0.50), favoring the antiparallel model. These results were obtained with 1789 (noon) and 1312 (midnight) data points. The slopes of the regression lines indicate 29% IMF By entry at noon and 79% at midnight. The local‐time distribution of the slopes varies smoothly from midnight peak to a broad minimum near noon.
Stability of hydrous phases in the transition zone and the upper most part of the lower mantle
Authors: Ohtani Eiji , Shibata Takeo , Kubo Tomoaki , Kato Takumi
Published: February 2004

Phase relation for Mg2SiO4+20.4 wt.%H2O composition was studied in the pressure range from 11 GPa to 22.5 GPa. The sequence of the phase transitions in the temperature range from 800°C to 1000°C with increasing pressure was as follows; Forsterite + Water → Phase A + Clinoenstatite + Water → Phase E + Water → Superhydrous phase B + Phase F + Water → Brucite + Phase F (+Water). Coexistence of brucite and phase F was observed at pressures above 20 GPa. These phases are stable at least up to 22.5 GPa and around 1000°C, and are the candidates for the hydrous phase in a cold slab descending into the base of the transition zone and the uppermost part of the lower mantle.
The relationship of leader and return stroke processes in cloud‐to‐ground lightning
Authors: Mazur Vladislav , Ruhnke Lothar H. , Laroche Pierre
Published: February 2004

The unique relationship between the leader and return stroke in cloud‐to‐ground flashes and the ambient cloud potential distribution is formulated. This relationship in the form of a ratio of an electric field produced by a leader, ΔEl, to that of a return stroke, ΔEr, is analyzed for two electrostatic leader models, the bi‐directional leader and the Schonland “source charge” models, and is then compared with field measurements. It is found that the ΔEl/ΔEr ratios of real flashes fall between the curves of the ratios calculated for the two leader models, with each model representing an extreme condition of ambient electric field distribution.
Simultaneous observation of convective adjustment and turbulence generation in the mesosphere
Authors: Lehmacher Gerald , Lübken Franz‐Josef
Published: February 2004

We present simultaneous in situ measurements of turbulence and temperature in the midlatitude mesosphere obtained as part of the DYANA campaign on March 13, 1990 at Biscarrosse, France (44°N, 1°W). In this study, we have extended the temperature measurements of our rocket borne ionization gauge down to 70 km and directly compared them to the small scale density fluctuations. Between 74 and 81 km we observed a unique, sawtooth shape layer in the temperature profile with a slightly superadiabatic lapse rate. In the same region, strong turbulent density fluctuations were present. We interpret these observations as convective adjustment and associated turbulence.
Far‐UV emissions from the SL9 impacts with Jupiter
Authors: Ballester G. E. , Harris W. M. , Gladstone G. R. , Clarke J. T. , Prangé R. , Feldman P. D. , Combi M. R. , Emerich C. , Strobel D. F. , Talavera A. , Budzien S. A. , Vincent M. B. , Livengood T. A. , Jessup K. L. , McGrath M. A. , Hall D. T. , Ajello J. M. , ben Jaffel L. , Rego D. , Fireman G. , Woodney L. , Miller S. , Liu X.
Published: February 2004

Observations with the International Ultraviolet Explorer (IUE) during the impacts of the fragments of comet D/Shoemaker‐Levy 9 with Jupiter show far‐UV emissions from the impact sites within a ∼10 min time scale. Positive detections of H2 Lyman and Werner band (1230–1620 Å) and H‐Lyα emissions are made for impacts K and S, and marginally for P2. No thermal continuum is observed. The radiated far‐UV output was >1021 ergs. The H2 spectrum is consistent with electron collisional excitation if significant CH4 absorption is included. Such emissions could result from plasma processes generated by the impacts. Non‐thermal excitation by the high altitude entry and explosion shocks may also be relevant. Emissions by Al+ (1671 Å) and C (1657 Å) of cometary origin are tentatively identified.
Short‐term variability in marine atmospheric dimethylsulfide concentration
Authors: Ayers G. P. , Gillett R. W. , Ivey J. P. , Schäfer B. , Gabric A.
Published: February 2004

Dimethylsulfide (DMS) concentrations measured twice per hour in marine boundary layer air at the Cape Grim baseline station exhibit high variability over timescales as short as several hours. Major sources of this variability are identified as a diurnal cycle associated with the daytime destruction of DMS by reaction with hydroxyl radical, and a strong dependence upon wind speed, with high DMS concentrations at high wind speeds. The wind speed dependence was found to be broadly consistent with the wind speed dependence proposed by Liss and Merlivat [1986] for 10 m wind speed in the range 3.6 to 13 m s−1.
A 2,200 years periodicity in the Asian Monsoon System
Authors: Naidu Pothuri Divakar , Malmgren Björn A.
Published: February 2004

We have carried out a high‐resolution study of fluctuations in upwelling intensity along the Oman Margin, western Arabian Sea, through the last 19,130 years based on several marine microfossil indices of upwelling. We document a periodicity of 2,200 years in the upwelling indices, which would be governed by the south‐west (SW) monsoon with such a periodicity. Our data further demonstrate greater amplitude in the variability of the SW monsoon during the Holocene than during the last glacial period. Our reported 2,200 years periodicity has two implications (1) oceanic circulation changes partly influence monsoon strength at sub‐Milankovitch cycles (2) previously documented 2,300 years periodicity in atmospheric 14C might be induced by oceanic circulation changes.