bluuebunny/crossref_metadata_2025 huggingface dataset:
Latitude variations in interplanetary Lyman‐α data from the Galileo EUVS modeled with solar He 1083 nm images
Authors: Pryor W. R. , Barth C. A. , Hord C. W. , Stewart A. I. F. , Simmons K. E. , Gebben J. J. , McClintock W. E. , Lineaweaver S. , Ajello J. M. , Tobiska W. K. , Naviaux K. L. , Edberg S. J. , White O. R. , Sandel B. R.
Published: February 2004

Observations of interplanetary Lyman‐α obtained by the Galileo Extreme Ultraviolet Spectrometer (EUVS) experiment near solar maximum in 1990 show a distinct migration in the upwind brightness maximum from 36±5°N to 6±5°N ecliptic latitude over a period of several months. Our earlier models based on solar Lyman‐α flux proxies appropriate for use in the ecliptic plane ( Pryor et al., 1992; Ajello et al., 1994) capture the solar rotation effects present in the data, but do not reproduce this latitude migration. We introduce a new type of model that uses He 1083 nm images to produce a proxy for Lyman‐α as a function of both solar longitude and latitude. This model reproduces the observed latitude migration of the Lyman‐α brightness maximum.
The magnetic hysteresis properties of Ball‐milled monodomain titanomagnetite, Fe2.4Ti0.6O4
Authors: Brown A. P. , O'Reilly W.
Published: February 2004

Synthetic titanomagnetite, Fe2.4Ti0.6O4 (TM60) was ground in a tungsten carbide ball mill for times up to 80 hours. Initially the material becomes “harder” (coercive force, Hc, and ratio of remanence to saturation, Mr/Ms, rise), which is explicable in terms of reduced particle size and reduced domain wall multiplicity. On further grinding the material becomes “softer”, as expected for monodomain particles with reducing volume. The “optical particle size” of typically 0.4 µm, determined from direct observation by SEM, is, however, ten times bigger than the “magnetic crystal size” inferred from an analysis of the hysteresis loop parameters. The small magnetic crystal size is consistent with the observed X‐ray line broadening. The two observations can be reconciled by inspection of Transmission Electron Micrographs which show an internal microstnicture which can be interpreted as the presence of “nanocrystals” within the particle envelope . The production of such nanocrystals by the grinding of particles is described in the materials science literature. It may be that a review of the rock magnetism literature describing the magnetic properties of “crushed grains” will discover features explicable in terms of nanocrystals.
Wavelet analysis and visualization of the formation and evolution of low total ozone events over northern Sweden
Authors: Weinberg Beth L. , Drayson S. Roland , Freese Katherine
Published: February 2004

The formation and development of abnormally low total ozone events (LOEs), which typically last an average of 3–4 days, are analyzed to determine conditions under which these events may form. Wavelet analysis is performed on 13 years of daily total column ozone (TOZ) obtained by the Nimbus‐7 Total Ozone Mapping Spectrometer each day of the record. With wavelet analysis, the contributions and relative phases of signal components may be ascertained at specific times of interest. Timescales relevant during LOEs are identified and the contributions and phase relations of all components present in the TOZ signal are compared for common patterns and features. For a location in Sweden, the formation of 96% of the 52 LOEs studied required that all components with timescales (τ) less than a maximum value (τmax) were present in their negative phases. This suggests that LOEs result from the simultaneous interaction of TOZ‐depleting processes. The number of interacting processes varies with season and location. In addition, two criteria are seen to prevail when LOEs form in this location. First, background conditions favorable for the development of an event exist; these occur when TOZ is in a spectral state where all components with Δτ1<τ<τmax are in their negative phases. Second, a process takes place that can force the remaining short‐timescale components (τ<Δτ1) into their negative phases. Processes associated with “initiating” timescales (Δτ1) of ≈ 2–6 days are found to be a key factor in the initiation of LOEs in this location. Although the background conditions are not uncommon, the likelihood that both criteria are simultaneously met is low and the occurrence of LOEs is indeed rare (averaging 4.7 events per year from 1980–1990).
Further evidence for inclination shallowing in red beds
Authors: Garcés Miguel , Parés Josep Maria , Cabrera Lluís
Published: February 2004

Red beds and related shallow marine siliciclastic sediments within the extensional Catalan Neogene basins offer a unique opportunity to study the relationship between sediment anisotropy, remanence acquisition and inclination shallowing. On the basis of the dominant fabric features, sedimentary facies are grouped into laminated, massive and bioturbated. The bulk susceptibility appears to be dominated by paramagnetic phyllosilicates and clay minerals. The magnetic susceptibility fabric is dominantly foliated while the degree of anisotropy is very variable and is dependent on the facies type. Strong foliation dominates in the laminated sediments whereas weak anisotropy characterizes the bioturbated and massive mass‐flow facies. Moreover, we observe a correlation between facies type and remanence inclination. The undisrupted thinly laminated facies provides the most biased inclination values: 20° as opposed to 60° of the expected geomagnetic field. Steeper inclinations are reported from bioturbated muds, while the best record of the geomagnetic inclination is found in the weakly anisotropic mass flow deposits.
238U‐230Th dating of a geomagnetic excursion in Quaternary basalts of the Albuquerque Volcanoes Field, New Mexico (USA)
Authors: Peate D. W. , Chen J. H. , Wasserburg G. J. , Papanastassiou D. A. , Geissman J. W.
Published: February 2004

We report the 238U‐230Th age derived from samples from three basalt flows from the Albuquerque Volcanoes Field, central New Mexico (USA), interpreted to have erupted during one of the Bruhnes Chron geomagnetic field polarity events. Whole‐rock samples and magnetite separates from two of the samples define an isochron with an age of 156±29 ka (2σ). It is now possible to determine the ages of geomagnetic excursions with reasonable precision, by the 238U‐230Th method, using basalts erupted between possibly 25 and up to 250 ka. Although a strict correlation of the polarity event recorded by the Albuquerque lavas with other high amplitude field phenomena in the latest Quaternary is not yet possible, the Blake and the less well‐documented Old Crow and Biwa I/Jamaica events are likely candidates.
Is the lower‐mantle rheology Newtonian today?
Authors: van den Berg Arie P. , Yuen David A.
Published: February 2004

The issue concerning the dominant creep mechanism in mantle convection has been studied numerically with a rheology incorporating both linear and non‐linear elements. We have employed a rheology suggested by the recently obtained melting temperature of lower‐mantle constituents. For an effective Rayleigh number between 105 and 106 this type of strongly temperature and pressure‐dependent rheology induces a circulation in the Earth's mantle, which is characterized by a sluggish type of flow in the lower mantle with a, prevailing Newtonian character, while in the upper mantle much more vigorous flows are developed in a predominantly non‐Newtonian rheology.
Systematic errors in seismic crosshole data: Application of the coupled inverse technique
Authors: Maurer H. R.
Published: February 2004

Systematic errors in seismic travel‐time data from mis‐located shot and receiver positions and/or systematic timing delays can distort considerably the results of tomographic inversions. Standard crosshole tomographic inversion algorithms do not account for systematic errors. Given sufficient data redundancy, the coupled inverse technique allows velocities, source and receiver coordinates and systematic delays to be reliably determined. Efficiency of a coupled inverse technique in crosshole applications is demonstrated through inversions of synthetic data sets and calculations of the formal resolution matrix. Tests revealed that shot delays may trade off with shot coordinates, but neither coordinates nor delays show strong dependencies or correlations with velocity parameters.
Seismic structure of the upper oceanic crust revealed by in situ Q logs
Authors: Goldberg D. , Sun Y.‐F.
Published: February 2004

In situ seismic attenuation is computed through 2.1 km of the upper oceanic crust in the vicinity of ODP Hole 504B. The results strongly tie crustal properties to seismic measurables and observed geological structures: we find that the attenuation can be used to define seismic layer boundaries and is closely related to the intensity of vertical heterogeneity. The in situ attenuation Q−1 consists of both intrinsic and scattering contributions, but is dominated by the scattering attenuation unless porosities are near zero, when it approaches typical estimates from seismic refraction studies. The attenuation is analytically modeled by multiple backscattering from heterogeneities observed in a sonic Vp log and is found to decrease step‐wise in relatively homogeneous layers from Q=25 to Q > 300 between the top of seismic layer 2A and a sharp discontinuity at 1.3 km depth. These changes correspond with heterogeneities at 1.0–1.3 m and at 5.6–10.0 m wavelengths that we interpret to be associated with fracturing and structure of pillow basalts and lava flows in seismic layers 2A and 2B. Although seismic velocity studies suggest that the layer 2/3 boundary also occurs at about 1.3 km, the large variation in Q (140 to 460) below this depth indicates that a seismically homogeneous and uniform layer 3 has not been reached in Hole 504B. We derive an empirical relationship between attenuation and porosity Q−1=Q0−1 eβϕ, where Q0−1=0.004 and β=25, that may be applicable at other oceanic crust locations and useful for constraining seismic inversion models.
Hydration and uplift of the oceanic crust on the Mid‐Atlantic Ridge associated with hydrothermal activity: Evidence from boron isotopes
Authors: Palmer M. R.
Published: February 2004

Boron isotope systematics of vent fluids from the Mid‐Atlantic Ridge (MAR) and the faster spreading East Pacific Rise (EPR) reveal that at the MAR ∼50% of seawater boron is removed from circulating fluids on the downwelling limb of the hydrothermal convection cell, whereas little boron is removed at EPR sites. Geophysical and petrographic studies suggest that downwelling fluids on the MAR penetrate deep in the oceanic crust and upper mantle where boron is removed during serpentinization of peridotite. The associated hydration of the oceanic crust reduces its density and modelling of the data suggests that this results in uplift, leading to significant elevation of the median valley walls in the vicinity of active hydrothermal systems.
Temporal variations in diffuse hydrothermal flow at TAG
Authors: Schultz A. , Dickson P. , Elderfield H.
Published: February 2004

We have obtained direct measurements of diffuse hydrothermal effluent temperature, velocity and chemistry from the TAG hydrothermal mound, 26°08′N, 44°49′W, Mid‐Atlantic Ridge. We report on the time series physical measurements obtained from a location on the eastern flank of the main summit complex. Several features were observed including strong tidal variability in flow, a conspicuous elevation of effluent temperatures during the period 11 October–17 October 1994, and a long term increase in temperature superimposed upon all other trends. The six‐day‐long temperature excursion is coincident with increases in sediment and effluent temperatures observed by instruments left in place on the TAG mound by other workers. We have established through time‐lapse seafloor video observations and through drilling records that the mid‐October effluent temperature excursion is correlated closely with local drilling activity by the Ocean Drilling Program.
Dayside Pc5 pulsation detected by Viking ion data at L=4
Authors: Yamauchi M. , Lundin R. , Mursula K. , Marklund G. , Potemra T. A.
Published: February 2004

On September 12, 1986, when the largest magnetic storm (Dst = −157 nT) during Viking operations took place, the satellite observed unusual energy modulation of sub‐keV ring current ions. The modulation is seen in both the pitch angle domain (conic‐like distribution) and the space‐time domain (wavy variation of ion flux with a period of a few minutes). The wavy variation is synchronized with a clear and distinct magnetic field‐line oscillation which is probably a standing Alfvén wave. This is observed simultaneously on the ground as a Pc5 pulsation over a wider range of latitude than the satellite observation.
Mineralogy, chemical composition and structure of the MIR Mound, TAG Hydrothermal Field
Authors: Stepanova T. V. , Krasnov S. G. , Cherkashev G. A.
Published: February 2004

The study of samples collected from the surface of the MIR mound (TAG Hydrothermal Field) by video‐controlled hydraulic grab allowed identification of a number of mineralogical types. These include pyrite‐chalcopyrite (Py‐Cp), bornite‐chalcopyrite‐opaline (Bn‐Cp‐Op) and sphalerite‐opaline (Sp‐Op) sulfide chimneys, massive sulfides composed of pyrite (Py), chalcopyrite‐pyrite (Cp‐Py), marcasite‐pyrite‐opaline (Mc‐Py‐Op), sphalerite‐pyrite‐opaline (Sp‐Py‐Op) and sphalerite‐chalcopyrite‐pyrite‐opaline (Sp‐Cp‐Py‐Op), as well as siliceous and Fe‐Mn oxide hydrothermal deposits. Most of the minor elements (Ag, Au, Cd, Ga, Hg, Sb and Pb) are associated with Zn‐rich massive sulfides, Co Bi, Pb, and As with Ferich ones, while Cu‐rich sulfides are depleted of trace metals. Cu‐enriched assemblages are concentrated in the northern part, Zn‐enriched in the center, and siliceous rocks in the south of the MIR mound. According to paragenetic relations, the development of the mound started with the formation of quartz (originally opaline) rocks and dendritic assemblages of melnikovite‐pyrite, followed by deposition of chalcopyrite and recrystallization of primary pyrite, subsequent generation of sphalerite‐rich assemblages and final deposition of opaline rocks. The late renewal of hydrothermal activity led to local formation of Cu‐rich chimneys enriched in Au, Ag, Hg and Pb probably due to their remobilization from inner parts of the deposit.
Geomagnetic intensity and 14C abundance in the atmosphere and ocean during the past 50 kyr
Authors: Laj Carlo , Mazaud Alain , Duplessy Jean‐Claude
Published: February 2004

We have used a new sedimentary record of geomagnetic field intensity, combined with published volcanic data, to examine the extent to which geomagnetic changes have affected 14C production in the past. The production record was then converted into an atmospheric Δ14C signal using a 4‐box model of past oceanic circulation. The results indicate that changes in geomagnetic field intensity account for at least 80% of the Δ14C shift documented by published U‐Th data, which are of the order of 500 per mil with respect to a constant production hypothesis. Model simulations show that changes in past oceanic circulation account for only ±100 per mil of Δ14C variation, which is within the uncertainty of the geomagnetic correction. In terms of dating, these results show that the radiocarbon ages have to be shifted by 2 to 3.5 kyr towards older ages during the 20–40 ka interval.
Tidal loading in south western Europe: A test area
Authors: Francis O. , Melchior P.
Published: February 2004

The gravity attraction and loading effects computed on the basis of recent ocean tide models still present non negligible discrepancies for the principal tidal lunar wave M2. The installation of new tidal gravity stations in these regions would be useful to assess the accuracy of these new ocean tide models, in particular for the Atlantic ocean. This investigation clearly proves that there is a real scientific interest to set up a new Earth tides gravity profile along the coasts from Belgium to Portugal.
The evolution of material surfaces in convection with variable viscosity as monitored by a characteristics‐based method
Authors: Ten Arkady , Yuen David A. , Larsen Tine B. , Malevsky Andrei V.
Published: February 2004

We have studied the evolution of material surfaces in strongly time‐dependent convection for both Newtonian and non‐Newtonian temperature‐ and depth‐dependent rheologies. A spline‐characteristic method has been employed. The method of characteristics is second‐order in time and fourth‐order in space. Our strategy is to employ a very dense grid for the material surface field with about 50 to 100 times more points than for the temperature field grid. We have detected sharp entrainment of the surrounding material into both the ascending and descending flow structures. We have observed the breakoff process involving the descending plume. Mixing takes place very differently for the two rheologies. With time, small vortical features are developed inside the Newtonian plumes, while unmixed islands still persist in the non‐Newtonian flow.
Detection of He+ layering in the topside ionosphere over Arecibo during equinox solar minimum conditions
Authors: González Sixto A. , Sulzer Michael P.
Published: February 2004

We describe recent developments in and results from topside incoherent scatter radar (ISR) measurements at Arecibo, PR, emphasizing helium ion measurements. Recent improvements in the data taking modes and the data processing permit isolation of the concentrations of oxygen, helium and hydrogen ions between the F region peak and 2000 km with about 10 minute time resolution. The need for the three ion non‐linear least squares fits is justified by use of the goodness of fit; a two ion fit is shown to be unacceptable. The new measurements are optimized for the rapid height variations in the solar minimum nighttime ionosphere by replacing the traditional 1 ms pulse with a 500 µs pulse. We show results from one day of a five day experiment during the Spring of 1994. For these equinox solar minimum conditions, the altitude distribution of the helium ions usually has a maximum near the O+ to H+ transition altitude (ht), forming a distinct layer, most noticeable during the night. The maximum helium ion concentrations tend to be quite low, 2 or 3 × 10³ cm−3, or 10–20% of the topside plasma at the peak of the He+ layer. The transition altitude, ht, varies from about 1200 km to 1400 km during the day to near 500 km at night, and the He+ layer follows this altitude variation. Finally we show that the location of the layer near ht and its intensification during the night can be explained using ambipolar diffusion equations.
Ozone measurements in a tropopause fold associated with a cut‐off low system
Authors: Langford A. O. , Masters C. D. , Proffitt M. H. , Hsie E.‐Y. , Tuck A. F.
Published: February 2004

The two‐dimensional structure of a tropopause fold that formed on the western flank of a cut‐off cyclone over the western United States is examined through time series of vertical ozone profiles made using the NOAA Aeronomy Laboratory's Differential Absorption Lidar (DIAL) system at Fritz Peak Observatory (39.9°N, 105.3°W, 2.68 km above sea level). The observations are compared to calculated potential vorticity fields, and the net influx of ozone to the troposphere is estimated to be ∼5.5 × 1032 molecules assuming that the fold is irreversibly mixed into the troposphere below 8.5 km.
The ATLAS series of shuttle missions
Authors: Kaye Jack A. , Miller Timothy L.
Published: February 2004

The ATLAS space shuttle missions were conducted in March 1992, April 1993, and November 1994. The ATLAS payload and companion instruments made measurements of solar irradiance and middle atmospheric temperatures and trace gas concentrations. The solar irradiance measurements included total and spectrally resolved solar irradiance. The atmospheric measurements included microwave, infrared, and ultraviolet limb sounding, nadir ultraviolet backscatter, and solar occultation techniques. This paper introduces a special section in this issue of Geophysical Research Letters.
Indium concentration in Pacific seawater
Authors: Amakawa H. , Alibo D. S. , Nozaki Y.
Published: February 2004

The concentration of indium in the seawaters of the western North Pacific was measured by using isotope dilution inductively coupled plasma mass spectrometry (ID‐ICPMS). The data suggest a surface maximum and the profiles show a possible decrease with depth. The measured concentrations of indium range from 0.047 to 0.155 pmol/kg and are almost three orders of magnitudes lower than those reported for the North Pacific by Chow and Snyder [1969]. We believe that the earlier data reflect experimental artifacts. Our data are also lower by about one order of magnitude than those in the North Atlantic reported by Matthews and Riley [1970]. The possibility exists that their data also suffered from contamination problems. It is also likely that the concentration of indium in the Atlantic is indeed significantly higher than those in the Pacific due to the difference in the atmospheric input if indium behaves like A1. Redetermination of the Atlantic samples is essential to resolve the two possibilities.
Evidence for interannual and interdecadal climate variability in the South Atlantic
Authors: Venegas Silvia A. , Mysak Lawrence A. , Straub David N.
Published: February 2004

A singular value decomposition (SVD) analysis is used to determine the coupled modes of variability of monthly sea surface temperature (SST) and sea level pressure (SLP) data from the South Atlantic region, for the period 1953–1992. We find that the three leading SVD modes respectively account for 63%, 20% and 6% of the total square covariance. The first mode represents an approximately 15‐year period oscillation in the strength of the subtropical anticyclone, accompanied by fluctuations of a north‐south dipole structure in the SST. It appears to be linked to the global‐scale interdecadal (15‐year) joint mode in SST and SLP recently studied by Mann and Park. The second mode is characterized by east‐west displacements of the anticyclone center, in association with strong 6 to 7‐year period fluctuations of SST off the coast of Africa. The third mode is characterized by north‐south displacements of the anticyclone and 4‐year period fluctuations in the SST in a broad band across the central South Atlantic. This mode is strongly correlated with ENSO.
A new determination of Jupiter's radio rotation period
Authors: Higgins Charles A. , Carr Thomas D. , Reyes Francisco
Published: February 2004

The result of a measurement of the period of rotation of Jupiter's inner magnetosphere with unprecendented precision is presented. The measurement was made from the University of Florida database of 35 apparitions of Jovian decametric observations at frequencies of 18, 20, and 22 MHz between 1957 and 1994. The mean of our 24 independent measurements was 9h55m29s.685, and the standard deviation of the mean was 0s.0034. The System III (1965) Jovian rotation period value that is currently accepted by the International Astronomical Union is greater than our value by 7.4 times our standard deviation; it appears to be in need of revision. We set an upper limit of 27 milliseconds per year on a possible drift of the rotation period as measured by our method.
Estimation of fracture zone geometry from steady‐state hydraulic head data using iterative sequential cokriging
Authors: Renshaw Carl E.
Published: February 2004

The hydrogeology of fractured crystalline rock is often controlled by a few highly conductive features such as faults and/or fractures zones. Accurate modeling of fluid flow and transport in these systems requires that the geometry of these conductive features be characterized explicitly. A new method for estimating the geometry of these features is presented. The method is an extension of the recently developed geostatistical technique of sequential cokriging. In this extension, the geometry of the fracture zone is iteratively updated until an update increases the discrepancy between the estimated and observed hydraulic heads. Results from two hypothetical examples demonstrate that the method can accurately estimate the geometry of highly conductive fracture zones.
Validation of NOAA‐9 SBUV/2 total ozone measurements during the 1994 Antarctic Ozone Hole
Authors: Lienesch J. H. , Planet W. G. , DeLand M. T. , Laamann K. , Cebula R. P. , Hilsenrath E. , Horvath K.
Published: February 2004

The Solar Backscatter Ultraviolet (SBUV/2) instrument on the NOAA‐9 spacecraft made total ozone measurements over Antarctica during the 1994 Austral Spring depletion. These measurements continue those made by the SBUV/2 on NOAA‐11. In recent years NOAA‐9 drifted from a poor orbit to one where earth observations and calibration capabilities are not restricted. An interim calibration of the NOAA‐9 SBUV/2 instrument was established with data from June 1994 and applied to observations during September, October, and November 1994. To validate the NOAA‐9 ozone measurements, daily zonal ozone averages from NOAA‐9 and NOAA‐11 measurements in the Northern Hemisphere have been compared. Comparisons have also been made with ground‐based measurements from five Dobson stations dispersed on the Antarctic continent. The results show that, on average, the NOAA‐9 data agree to within 1–2 percent with the Dobson stations with standard deviations of the difference ranging from 5.3 to 7.7% and to within several percent with NOAA‐11 Northern Hemisphere data when restricted to solar zenith angles less than 80 degrees. This agreement makes possible not only a continuation of the Antarctic measurements without a large instrument‐related bias, but also establishes the NOAA‐9 data as a suitable transition data set during the replacement of NOAA‐11 by NOAA‐14.
New kinetic evidence for the near‐Earth reconnection
Authors: Fujimoto M. , Nakamura M. S. , Nagai T. , Mukai T. , Yamamoto T. , Kokubun S.
Published: February 2004

An anomalously large southward Bz (−23 nT) is detected in association with tailward jet (1600 km/s) by GEOTAIL at XGSM = −46 RE. Variations of MHD parameters suggest that the large southward Bz is caused by piling‐up of reconnected field lines by the jet against the standing plasma sheet. In addition, the ion distribution at the time of the large southward Bz is found to show a counter streaming ions (CSI) feature. A hybrid simulation of a reconnection process not only reproduces this feature, but also proves that the CSI ions are from both the lobes. Taking this CSI feature as new kinetic evidence that both the lobes are magnetically connected, we firmly conclude that the event is interpreted in terms of near‐Earth reconnection.
Measurement of atmospheric NO3 1. Improved removal of water vapour absorption features in the analysis for NO3
Authors: Aliwell S. R. , Jones R. L.
Published: February 2004

Atmospheric measurements of the nitrate radical generally detect its absorption of visible radiation in the band near 662 nm. This band is negatively correlated with strong absorptions due to tropospheric water vapour which must therefore be fitted in the spectral analysis to reduce the spectral residual to the level at which sufficient sensitivity to NO3 can be obtained. Previously this had been fitted using a cross‐section typically derived from spectra obtained just before sunset or just after sunrise which took no account of the diurnal variation in temperature and water vapour column amounts. An improved method of accounting for water vapour absorptions is presented here. When fitted together with their temperature dependence, water vapour cross‐sections calculated using a line‐by‐line approach gave a more accurate fitting of water vapour absorptions, thus improving the analysis for NO3.
Measurement of atmospheric NO3 2. Diurnal variation of stratospheric NO3 at midlatitude
Authors: Aliwell S. R. , Jones R. L.
Published: February 2004

NO3 total column abundances covering the diurnal cycle were measured at midlatitude (52.4°N) during May 1995 by visible absorption spectroscopy using the Moon as a light source. The variation of measured slant column amounts with lunar zenith angle indicated that the NO3 was chiefly located within the stratosphere. Model calculations of the diurnal variation of NO3 at the measurement site give systematically lower column abundances than the measurements. This discrepancy may be explained by uncertainties in rate and equilibrium constant data used in the model calculations. A value for the equilibrium constant for N2O5 thermal decomposition of 2.7 ×1 0−27 exp(10500/T) cm³ molec.−1 and exp[−2425/T] for the activation energy of the reaction of O3 with NO2 to produce NO3 are suggested from the fit of modelled to experimental data.
An assessment of the total ozone mapping spectrometer for measuring ozone levels in a solid rocket plume
Authors: Syage Jack A. , Ross Marty N.
Published: February 2004

The question whether the total ozone mapping spectrometer (TOMS) is capable of measuring ozone levels in a solid rocket motor plume is examined. Simulated measurements were computed for a chemical kinetics and dispersion model of a Titan IV plume. The principal disadvantage of TOMS for measuring local plume ozone levels is that the detection field‐of‐view is typically much larger than the column area for ozone loss. A secondary problem is attenuation of backscattered light by plume species and particles that can distort the ozone measurement.
Global Positioning System measurements of Indian Plate Motion and convergence across the lesser Himalaya
Authors: Freymueller J. , Bilham R. , Bürgmann R. , Larson K. M. , Paul J. , Jade S. , Gaur V.
Published: February 2004

We use Global Positioning System (GPS) measurements acquired from 1991 to 1995 to constrain the motion of sites in Bangalore, in southern India, and Kathmandu, Nepal, relative to a global GPS network. These measurements permit estimates of the northward motion of the Indian plate and convergence between the southern Himalaya and the Indian subcontinent. The velocities of Bangalore and Kathmandu in the ITRF92 reference frame agrees with that predicted by the NNR‐NUVEL1A plate motion model for Indian plate motion, and differ from that predicted for the Australian plate, confirming the independent motion of the Indian and Australian plate fragments. No significant motion was detected between Bangalore and Kathmandu during the three years from 1991–1994, even though Kathmandu is located in the hanging wall of the active Himalayan thrust system. The Himalayan thrust system is thought to accommodate 18±7 mm/yr of convergence and has been the source of several historic M ∼ 8 earthquakes. The absence of motion of Kathmandu relative to the Indian plate can be explained if the thrust system is presently locked south of the Greater Himalaya. Our preferred model has no steady slip on the detachment south of the Greater Himalaya, and steady slip at a rate greater than 6 mm/yr (1/3 of the long‐term convergence rate) can be ruled out at 95% confidence level.
The origin of large scale structure in mantle convection: Effects of plate motions and viscosity stratification
Authors: Bunge Hans‐Peter , Richards Mark A.
Published: February 2004

Convection in Earth's mantle is dominated by long‐wavelength structure, as evidenced by the very “red” spectra of both seismic velocity heterogeneity in the deep mantle and the non‐hydrostatic gravity field, or geoid. Here we show that this large‐scale structure may be a consequence of two factors that influence the scale of mantle convection. First, the existence of surface plates, which tend to organize the flow. Second, a substantial increase in lower mantle viscosity for which there is considerable independent geophysical evidence. Combining these two factors in 3‐D spherical mantle convection models explains rather well the observed seismic spectrum of mantle heterogeneity.
Role of photospheric footpoint shear in the impulsive dynamics of the solar corona
Authors: Ma Z. W. , Bhattacharjee A.
Published: February 2004

A frequently observed feature of a solar flare is its impulsive growth from a relatively quiescent background. This imposes a significant constraint on magnetic reconnection models which propose to account for flares: not only should the time scale be fast, but it must also exhibit an impulsive character. It is shown that the spatial width of the shearing motion of the photospheric footpoints has a significant qualitative effect on the time‐evolution of the current sheet and the reconnection electric field in a two‐dimensional coronal loop with a neutral line. The reconnection dynamics for localized footpoint shear profiles does not show an impulsive phase and occurs on a Sweet‐Parker time scale (∼ η−1/2), whereas the reconnection dynamics with broad shear profiles occurs on a faster time scale with a weaker dependence on the resistivity (∼η−1/5), and furthermore, exhibits an impulsive phase due to flux pile‐up near the reconnection layer.
The relation between the northern polar cap and auroral electrojet geomagnetic indices in the wintertime
Authors: Vassiliadis D. , Angelopoulos V. , Baker D. N. , Klimas A. J.
Published: February 2004

The polar cap (PC) index is a measure of the high‐latitude geomagnetic disturbances due to Hall and field‐aligned currents. The index is well correlated with the auroral electrojet AL and AUindices (correlation with the PC index is 76% and 66%, resp.). Here we obtain several types of data‐based models that relate the PC to the AL and AU indices in the wintertime, when the ionospheric conductivity is mostly due to the precipitating particles of the field‐aligned currents. The new models predict AL and AU from PC with correlations much higher than those found by earlier studies. Thus linear moving‐average filters reproduce the observed AL with a correlation of 88% (AU: 75%) while linear autoregressive moving‐average (ARMA) models based on the PC index produce in‐sample single‐step predictions with 98% and 97% correlations with AL and AU respectively. For long‐term, out‐of‐sample prediction, the linear ARMA prediction from the PC index has an asymptotic prediction error which is at least 25% more accurate than the prediction from solar wind input. Nonlinear models are slightly more accurate than their linear counterparts, indicating a weak nonlinearity in the relation between the polar cap and auroral zone indices. The prediction‐observation correlations are sufficiently high that models based on the PC index can be used for specification of the auroral geomagnetic activity.
A comparison of ambipolar diffusion coefficients in meteor trains using VHF radar and UV lidar
Authors: Chilson Phillip B. , Czechowsky Peter , Schmidt Gerhard
Published: February 2004

In this paper we present the first comparative estimations of ionic diffusion rates for sporadic meteor trains near the mesopause made using VHF radar and UV Rayleigh lidar observations. In both cases we initially assumed that the meteor trains dissipate primarily through ambipolar diffusion. For the radar data, the diffusion coefficient within the meteor train was determined from the decay rate of the backscattered power. From the the lidar data we then calculated profiles of the atmospheric temperature and density in the height range at which the meteor echoes were detected. These data were used to estimate the ambipolar diffusion coefficients that would result assuming different species of ions. Our results appear consistent with the notion that short‐lived underdense meteor trains in the height range of 85–95 km decay primarily by ambipolar diffusion. However, the diffusion coefficients obtained from the radar observations were smaller than those found from the lidar data assuming metal meteoric ions. One possible explanation could be that the radar meteor echoes resulted from ionized constituents of the atmosphere.
First‐principles calculation of the equation‐of‐state, stability, and polar optic modes of CaSiO3 perovskite
Authors: Chizmeshya Andrew V. G. , Wolf George H. , McMillan Paul F.
Published: February 2004

We report the results of a first‐principles LAPW calculation of the equation‐of‐state, dynamic stability, and infrared‐active transverse optic vibrational mode frequencies of CaSiO3 perovskite. A Birch‐Murnaghan fit to the computed energy‐volume relation of the cubic phase yields values of Vo=45.62 Å³, Ko=227 GPa, and Ko′=4.29 for the thermally‐corrected equation‐of‐state parameters. These values are in excellent agreement with recent quasi‐hydrostatic compression data to 10 GPa, but significantly differ from values derived from higher pressure non‐hydrostatic compression data. We calculate the volume dependence of the infrared‐active TO mode frequencies using a frozen‐phonon approach. The lowest frequency ferroic mode is predicted to occur near 228 cm−1 at ambient pressure and displays classic soft‐mode behavior in the tensile regime, in quantitative agreement with earlier molecular and lattice dynamical calculations, based on empirical potentials. These established a link between the low frequency ferroic mode and the thermally activated crystalline‐amorphous transition in a model CaSiO3 perovskite system. Our present calculations also reveal that the static cubic perovskite structure is unstable with respect to small octahedral rotations, corresponding to Brillouin zone edge dynamical instabilities, at ambient pressure and throughout the pressure range of the lower mantle. We speculate that coupling of the low frequency ferroic mode with octahedral tilting modes and strain lower the activation energy for the crystalline‐amorphous transition.
Ozone variability in the upper stratosphere during the declining phase of the solar cycle 22
Authors: Chandra S. , Froidevaux L. , Waters J. W. , White O. R. , Rottman G. J. , Prinz D. K. , Brueckner G. E.
Published: February 2004

Recent studies of the solar cycle variation of ozone have shown that the response of ozone in the upper stratosphere to solar UV variation, as inferred from the SBUV (Solar Backscatter Ultraviolet) type measurements, is about a factor of two greater than estimated from 2‐D photochemical models. Because of potential errors in accounting for the long term instrument drift in the SBUV type of measurements, the significance of this discrepancy is difficult to quantify. In this paper, ozone measurements from the Microwave Limb Sounder (MLS) and the solar irradiance measurements from the Solar Stellar Irradiance Comparison Experiment (SOLSTICE) and the Solar Ultraviolet Irradiance Monitor (SUSIM) onboard the Upper Atmosphere Research Satellite (UARS) are analyzed to estimate the upper stratosphere ozone response to changes in the solar UV irradiance. During the three year period of UARS measurements, analyzed here for the declining phase of the solar cycle 22, the solar irradiance in the 200–205 nm range decreased by about 5 % from a near solar maximum to a near solar minimum level. During the same period, ozone mixing ratio measured from the MLS instrument decreased by about 2–4% in the 0.7–3 hPa region. In the upper stratosphere, the general characateristics of the MLS time series are similar to those inferred from the NOAA‐11 SBUV/2 measurements. The SBUV/2 trends above 1.5 hPa, however, are significantly greater than those derived from the MLS data. The UARS data suggest that the long term solar UV response of ozone in the upper stratosphere is underestimated by 2‐D photochemical models as in previous studies based on the SBUV type measurements.
Ion populations on open field lines within the dayside low‐latitude boundary Layer: Theory and observations during a transient event
Authors: Lockwood M. , Moen J.
Published: February 2004

We analyze of ion populations observed by the NOAA‐12 satellite within dayside auroral transients. The data are matched with an open magnetopause model which allows for the transmission of magnetosheath ions across one or both of the two Alfvén waves which emanate from the magnetopause reconnection site. It also allows for reflection and acceleration of ions of magnetospheric origin by these waves. From the good agreement found between the model and the observations, we propose that the events and the low‐latitude boundary precipitation are both on open field lines.
Implications of Io's magnetic signature: Ferromagnetism?
Authors: Cheng A. F. , Paranicas C.
Published: February 2004

The Galileo spacecraft recently measured an ≈ 40% decrease of Jupiter's magnetic field near Io from a distance of 0.5 RIo [Kivelson et al., 1996], a signature that cannot be explained in terms of the previously known Alfven wing current system alone. The Galileo observations can be explained by an additional magnetic moment of Io aligned with the ambient Jovian field. There is no Earth‐like magnetosphere at Io because its magnetic moment is not sufficient to stand off the Jovian field far above Io's atmosphere. The Alfven wing current system must close within the Io interior, implying an electrical conductivity in the outer layers much higher than that expected for solid rock alone. Since widespread sulfur‐rich aquifers are present to support Io's extensive volcanism, the thermal and electrical conductivities in Io's outer layers will be higher than would be the case for solid rock. We suggest that on average the temperature remains below the Curie point to a depth on the order of at least 300 km. Io's magnetic moment could then be explained as thermoremanent magnetization of ferromagnetic material. In this model, Io's outer layers cooled through the Curie temperature in a magnetic field about 15 times the current ambient field at Io. At that time, Io was closer to Jupiter, and/or Jupiter's dynamo magnetic moment was stronger.
Seismic evidence for stretched continental crust in the Japan Sea
Authors: Kurashimo Eiji , Shinohara Masanao , Suyehiro Kiyoshi , Kasahara Junzo , Hirata Naoshi
Published: February 2004

The Japan Sea is a major marginal sea in the western Pacific comprised of basins and bathymetric highs. Technically, these features were created by multiple‐rifting and spreading processes, as exemplified in the creation of the Japan Basin and Yamato Basin. However, there are smaller scale features for which seismic crustal models have been inadequate to infer or verify their origin and evolution. Recent advances in marine seismological surveys enable us to obtain heterogeneous seismic crustal structures in sufficient detail to characterize these features. In September of 1992, a seismic experiment was conducted to obtain the detailed seismic crustal structure in the southwestern part of the Japan Sea, including the basin and bank areas. Seventeen ocean bottom seismometers (OBSs) were deployed on two lines. Explosives and airguns were fired as controlled seismic sources. The model of the crust obtained in the northern Tsushima Basin is about 13 km thick including a 1.5‐km‐thick sedimentary layer. Beneath the bank area the crust is 22 km thick and the upper crust is relatively homogeneous with a P‐wave velocity of about 6 km/s. The bank is interpreted to be a stretched continental crust fragment.
On the use of carbon tetrachloride as a transient tracer of Weddell Sea deep and bottom waters
Authors: Meredith Michael P. , Van Scoy Kim A. , Watson Andrew J. , Locarnini Ricardo A.
Published: February 2004

Antarctic bottom waters have long been known to be a mixture of Circumpolar Deep Water and Shelf Water. Recent observations show that in the Antarctic bottom waters of the Scotia Sea and northern Weddell Sea, the ratios of carbon tetrachloride (CCl4) to chlorofluorocarbons (CFC‐11, 12) are inconsistent with the ratios observed in the surface layer of the Weddell Sea. This is the result of a deficit of CCl4 in the bottom waters, and renders the compound unsuitable for use as a transient tracer from which apparent ages can be derived directly. The summer near‐surface temperature minimum of Antarctic Surface Water exhibits a similar inconsistency, demonstrating that CCl4 can be removed from cold waters with high oxygen levels, probably through a biological process. It is inferred that Shelf Water features a similar CCl4 deficit which is transferred to the new Antarctic bottom waters upon formation, accounting for the observed deep CCl4 deficit.
Solar wind control of Jovian electron flux: Pioneer 11 analysis
Authors: Morioka Akira , Tsuchiya Fuminori
Published: February 2004

The relations between Jovian electron flux and the solar wind were investigated using energetic particle and solar wind parameter data from Pioneer 11. The cross‐correlation study disclosed that the flux change of Jovian electrons observed in interplanetary space showed an anti‐correlation with the solar wind variation, suggesting that the release of Jovian electrons was controlled by the solar wind at the Jovian magnetosphere. It was also confirmed from simulation models that the modulation of the electron flux in interplanetary space was the result of both the above “source modulation” by the solar wind in the outer magnetosphere of Jupiter and the “barrier effect” induced by the co‐rotating interaction region (CIR) in the solar wind.
Prediction of magnetic storms by nonlinear models
Authors: Valdivia J. A. , Sharma A. S. , Papadopoulos K.
Published: February 2004

The strong correlation between magnetic storms and southward interplanetary magnetic field (IMF) is well known from linear prediction filter studies using the Dst and IMF data. However, the linear filters change significantly from one storm to another and thus are limited in their predicting ability. Previous studies have indicated nonlinearity in the magnetospheric response as the ring current decay rate varies with the Dst value during storms. We present in this letter nonlinear models for the evolution of the Dst based on the OMNI database for 1964–1990. When solar wind data are available in advance, the evolution of storms can be predicted from the Dst and IMF data. Solar wind data, however, are not available most of the time or are available typically an hour or less in advance. Therefore, we have developed nonlinear predictive models based on the Dst data alone. In the absence of solar wind data, these models cannot predict the storm onset, but can predict the storm evolution, and may identify intense storms from moderate ones. The input‐output model based on IMF and Dst data, the autonomous model based on Dst alone, and a combination of the two can be used as forecasting tools for space weather.
Observations of the two‐day wave in WINDII data during January, 1993
Authors: Ward W. E. , Wang D. Y. , Solheim B. H. , Shepherd G. G.
Published: February 2004

Analysis of variations in the zonal and meridional wind observed by the Wind Imaging Interferometer (WINDII) on the Upper Atmosphere Research Satellite (UARS) from January 19 to January 31, 1993 reveal a strong quasi two‐day wave (QTDW) signature. These observations were taken during the time of peak amplitude for this QTDW event [Wu et al., 1993] and extend from 41°N to 71°S. Daytime and nighttime results are presented for the altitude ranges 90 to 150 km and 90 to 102 km respectively. The QTDW is found to occur with significant amplitude well into the winter hemisphere and lower thermosphere. Its latitudinal structure below 103 km is found to be similar to that calculated by Hagan et al. [1993] using the background wind profile of Portniagin and Solov'yeva [1992]. The peak amplitude occurs at 94 km with a magnitude of about 50 m/s for the meridional wind and 30 m/s for the zonal wind. Mean profiles from the summer midlatitudes show a secondary maximum in amplitude near 115 km and a node at 130 km. Above 130 km the wave appears to be evanescent.
Application of separatrix crossing theory to nondiffusion model of current sheet resonance
Authors: Savenkov B. V. , Zelenyi L. M.
Published: February 2004

The resonance phenomenon in charged particle dynamics in the Earth's magnetotail is investigated in terms of quasiadiabatic theory. The resonant properties of particle motion are found to be related to non‐diffusion chaotic migration and separatrix crossings.