bluuebunny/crossref_metadata_2025 huggingface dataset:
Solar wind speed structure in the inner corona at 3–12 Ro
Authors: Woo Richard
Published: February 2004

Estimates of solar wind speed obtained by Armstrong et al. [1986] based on 1983 VLA multiple‐station intensity scintillation measurements inside 12 Ro have been correlated with the electron density structure observed in white‐light coronagraph measurements. The observed large‐scale and apparently systematic speed variations are found to depend primarily on changes in heliographic latitude and longitude, which leads to the first results on large‐scale speed structure in the acceleration region of the solar wind. Over an equatorial hole, solar wind speed is relatively steady, with peak‐to‐peak variations of 50 km/s and an average of 230 km/s. In contrast, the near‐Sun flow speed across the streamer belt shows regular large‐scale variations in the range of 100–300 km/s. Based on four groups of data, the gradient is 36 km/s per degree in heliocentric coordinates (corresponding to a rise of 260 km/s over a spatial distance on the Sun of two arcmin) with a standard deviation of 2.4 km/s per degree. The lowest speeds most likely coincide with the stalks of coronal streamers observed in white‐light measurements. The detection of significant wind shear over the streamer belt is consistent with in situ and scintillation measurements showing that the density spectrum has a power‐law form characteristic of fully developed turbulence over a much broader range of scales than in neighboring regions.
Morphologic identification of Venusian lavas
Authors: Bruno Barbara C. , Taylor G. Jeffrey
Published: February 2004

Two independent methods are applied to Venusian lavas. First, fractal properties of 30 lavas are used to identify a'a, pahoehoe and transitional morphologies. Eighteen of these flows are then categorized into these same morphologies based on their radar signal. The techniques produce similar identifications, lending confidence to the fractal identification of those flow margins that could not be studied by the radar technique. Three of these flow margins are of lavas in Mylitta Fluctus, a flood basalt. Our fractal analysis suggests all 3 margins were emplaced as a'a flows, which has implications for the emplacement of large lava plateaux in general.
The Einstein Coefficient for spontaneous emission of the O2(a¹Δg) state
Authors: Mlynczak Martin G. , Nesbitt David J.
Published: February 2004

Recently reported measurements of the absorption band strength (i.e., the Einstein B‐coefficient for absorption) for the transition O2(X3Σg → a1Δg) at 1.27 µm, when correctly reanalyzed in this paper, indicate that the Einstein A‐coefficient for spontaneous emission of radiation is 1.47 × 10−4 s−1. This is a factor of 1.75 smaller than the value of 2.58 × 10−4 s−1 that has been used almost exclusively in the aeronomy field for the past 30 years. The determination of the new A‐value is reviewed, with an emphasis on the derivation of the appropriate ratio of the degeneracies of the upper and lower states of this transition. The new A‐value implies that ozone concentrations as inferred from measurements of O2(a¹Δg) emission must be increased significantly in existing databases and also that the efficiency of solar heating in the Hartley band of ozone is larger than previously calculated.
Detection of HBr and upper limit for HOBr: Bromine partitioning in the stratosphere
Authors: Johnson D. G. , Traub W. A. , Chance K. V. , Jucks K. W.
Published: February 2004

We determine mixing ratio profiles for HBr and upper limits for HOBr in the stratosphere with precisions up to 1.7 and 4.8 parts per trillion, respectively, using the combined data from 7 flights of our far‐infrared spectrometer. The measurements suggest that in the range 22–34 km the average mixing ratio of HBr is 2.0±0.8, and that the average mixing ratio of HOBr is less than 2.8 ppt. Our measurements of HBr are in reasonable agreement with a photochemical model which includes 0 or 2% production of HBr through the reaction of BrO with HO2, but in strong disagreement with a model including 5 or 10% HBr production.
A comparison of J‐values from the composition and photodissociative flux measurement with model calculations
Authors: McElroy C. T. , Midwinter C. , Barton D. V. , Hall R. B.
Published: February 2004

The first measurements of the spectral flux on a horizontal surface, limb brightness and apparent surface brightness beneath the NASA ER‐2 research aircraft were made during the Stratospheric Photochemistry, Aerosol and Dynamics Expedition (SPADE) of the NASA High‐Speed Research Program. Results from the May, 1993 campaign are presented. J‐values for the production of O(¹D) from the photodissociation of ozone and the photodissociation rate of NO2 to form NO have been determined and are compared to the currently used, modelled values.
Shallow seismic reflection profiling over a Mylonitic Shear Zone, Ruby Mountains‐East Humboldt Range Metamorphic Core Complex, NE Nevada
Authors: Hawman Robert B. , Ahmed Hishameldin O.
Published: February 2004

Seismic reflection profiling carried out with a sledgehammer source has imaged Tertiary extensional structures over a depth range of 45–500 m within lower plate rocks of the Ruby Mountains‐East Humboldt Range metamorphic core complex. The 400‐m CMP profile straddles an exposed contact between tectonic slices of dolomitic marble and metaquartzite emplaced by low‐angle ductile‐brittle normal faulting. Subhorizontal reflections from layering within the tectonic slices give way at 160 ms (160–220 m depth) to reflections that dip 15–45° to the east, in contrast with dips indicated in a poorly imaged segment of a coincident regional seismic line but in agreement with dips of foliation mapped for nearby up‐plunge exposures of a late Proterozoic ‐ early Cambrian sequence of metaquartzites, marbles, schists, and granitic rocks that forms the bulk of the underlying shear zone. Differences with the regional profile are attributed to the higher frequencies (30–100 Hz) generated by the smaller hammer source and the enhanced lateral resolution provided by the straighter profile and much smaller shot‐receiver offsets (46–157 m) contributing to the stack for each CMP. The results suggest that the near‐surface, east‐dipping component of the anastomozing shear zone extends at least 2 km farther east than previously interpreted. Rough estimates of interval velocities (1500–4500 m/s) inferred from stacking velocities are consistent with velocities of mylonitic rocks measured perpendicular to foliation at low confining pressures when the effects of macroscopic fractures and joints are taken into account. Peaks in amplitude spectra of stacked traces suggest long‐wavelength components of layering resolved at scales from 5–8 m (depth: 50 m) to 15–25 m (depth: 500 m).
Changes in Jupiter's 13‐cm synchrotron radio emission following the impact of comet Shoemaker‐Levy‐9
Authors: Klein M. J. , Gulkis S. , Bolton S. J.
Published: February 2004

Results of an observing program to monitor the synchrotron radio emission from Jupiter's inner radiation belts before, during and after the impact of Comet SL‐9 are reported. The observations were made at 2295 Mhz as part of the NASA‐JPL Jupiter Patrol, a long‐term radio astronomy monitoring program begun in 1971. The data indicate that the intensity of the synchrotron emission at 13 cm wavelength increased by 27 percent within a few days after the comet impacts; the longitudinal beaming curve was distorted during the week of impacts; the magnetic latitude beaming curves flattened after the week of impacts suggesting an increase in the emission at higher magnetic latitudes; and the decay of the enhanced emission is consistent with an exponential with a time constant of ∼125 days. The reported changes following the SL‐9 impact are unprecedented in the 23‐year history of the Jupiter Patrol.
Fate of ClNO2 over aqueous solutions containing iodide
Authors: George Ch. , Behnke W. , Scheer V. , Zetzsch C. , Magi L. , Ponche J. L. , Mirabel Ph.
Published: February 2004

The uptake of nitryl chloride ClNO2 by pure water and NaI solutions was studied as a function of temperature in the range from 268 to 279 K with the droplet train technique. An upper limit of 10−5 was derived for the uptake on pure water, while the uptake rate was observed to be greatly enhanced in the presence of 10−3–10−2 M iodide, yielding uptake coefficients in the range from 1.1 × 10−3 to 6.6 × 10−3. This enhancement is a consequence of a reaction between I− and ClNO2 where we suggest that a transfer of Cl+ to iodide is involved. We also suggest that bulk kinetics alone is unable to describe the measured uptake rate which is influenced by surface reactions. These results show that heterogeneous chemistry in concentrated aerosols may play an important role for the fate of ClNO2, and may affect the concentration of atomic chlorine in the marine boundary layer.
Scale‐dependent resistivity measurements of oracle granite
Authors: Jones Jay W.
Published: February 2004

A series of cross‐hole and single‐hole electrical conductivity measurements were made within saturated Oracle granite. The tests, performed with point source and point reference electrodes (pole‐pole or normal array), were designed to examine the equivalent homogeneous conductivity as a function of the rock volume by increasing the interelectrode separation. The length scale of the tests ranged from 8 inches to over 100 feet. Analysis of the data showed that (1) a power‐law relationship was observed where the electrical conductivity increased (resistivity decreased) with electrode separation; (2) exponential variograms were derived for all distance classes; thus, no finite variance was attained; (3) conductivity can be approximated as a nonhomogeneous, locally isotropic variable; and (4) the log of the apparent resistivity for a particular scale of measurement (i.e., at constant current/potential electrode distances) can be fit to a fractional Brownian motion (fBm) process and thus interpreted as a fractal process. Overall, cross‐hole and single‐hole electrical resistivity measurements proved to be an efficient technique to assess the electrical behavior of the fractured rock mass at the Oracle site.
Effective block size for imbibition or absorption in dual‐porosity media
Authors: Zimmerman Robert W. , Bodvarsson Gudmundur S.
Published: February 2004

A theoretical study is presented of liquid imbibition and solute absorption from a fracture network into a collection of matrix blocks of varying sizes and shapes. An individual irregularly‐shaped matrix block can be modeled with reasonable accuracy using the results for a spherical matrix block, by defining an effective radius ã = 3V/A, where V is the volume of the block and A is its surface area. In the early‐time regime, a collection of spherical blocks of different sizes can be replaced by an equivalent spherical block with a radius of aeq = −1, where the average is taken on a volumetrically‐weighted basis. In the long‐time limit, where no equivalent radius can rigorously be defined, asymptotic expressions are derived for the cumulative uptake as a function of the mean and the standard deviation of the radius distribution function, for both normal and lognormal radius distributions.
Intercomparison of global PAR data sets
Authors: Dye Dennis G. , Shibasaki Ryosuke
Published: February 2004

Global data sets of surface‐incident photosynthetically active radiation (PAR, 400–700 nm) from three satellite‐based methodologies are compared with each other and with ground data. Two are based on C1 data from the International Satellite Cloud Climatology Project (ISCCP): ISCCP‐BR was produced from an existing total shortwave irradiance data set by assuming 50% PAR; ISCCP‐PL is an existing PAR‐specific data set. TOMS PAR is based on 370 nm data from the Nimbus‐7 Total Ozone Mapping Spectrometer (TOMS). ISCCP‐BR and ISCCP‐PL are typically 12–16% and 8–12% greater than TOMS PAR, respectively. Comparison of ISCCP‐BR, ISCCP‐PL, and TOMS PAR with ground data at a mid‐latitude site for non‐winter (snow/ice‐free) months yields RMS differences of 28.1%, 13.7%, and 7.2%, and biases of +25.9%, +12.0%, and +2.8%, respectively. The comparison indicates TOMS PAR provides the most reliable estimates of PAR for snow/ice‐free, growing season months, i.e. when the energy is effective for photosynthesis. Differences among the data sets constitute a significant source of variation in results from biospheric process models that include PAR as a variable.
Double‐hump H+ velocity distribution in the polar wind
Authors: Barakat A. R. , Barghouthi I. A. , Schunk R. W.
Published: February 2004

The polar wind is an ambipolar plasma outflow from the terrestrial ionosphere at high latitudes. As the ions drift upward along geomagnetic flux tubes, they move from collision‐dominated (ion barosphere) to collisionless (ion exosphere) regions. A transition layer is embedded between these two regions where the ion characteristics change rapidly. A Monte Carlo simulation was used to study the steady‐state flow of H+ ions through a background of O+ ions. The simulation domain covered the collision‐dominated, transition, and collisionless regions. The model properly accounted for the divergence of magnetic field lines, the gravitational force, the electrostatic field, and H+‐O+ collisions. The H+ velocity distribution, f(H+), was found to be very close to Maxwellian at low altitudes (deep in the barosphere). As the ions drifted to higher altitudes, f(H+) formed an upward tail. In the transition layer, the upward tail evolved into a second peak with a kidney bean shape, and hence, f(H+) developed a double‐humped shape. The second peak grew with altitude and eventually became dominant as the ions reached the exosphere. This behavior is due to the interplay between the electrostatic force and the velocity‐dependent Coulomb collisions. Moreover, the H+ heat flux, q(H+), was found to change rapidly with altitude in the transition layer from a positive maximum to a negative minimum. This remarkable feature of q(H+) is closely related to the coincident formation of the double‐humped structure of f(H+). The double‐hump distribution might destabilize the plasma or, at least, cause enhanced thermal fluctuations. The double‐hump f(H+), and the associated wave turbulence, have several consequences with regard to our understanding of the polar wind and similar space physics problems. The plasma turbulence can significantly alter the behavior of the plasma in and above the transition region and, therefore, should be considered in future polar wind models. The wave turbulence can serve as a signature for the formation of the double‐hump f(H+). Also, more sophisticated (than the existing bi‐Maxwellian 16‐moment) generalized transport equations might be needed to properly handle problems such as the one considered here.
Correlated observations of HCl and ClONO2 from UARS and implications for stratospheric chlorine partitioning
Authors: Dessler A. E. , Considine D. B. , Morris G. A. , Schoeberl M. R. , Russell J. M. , Roche A. E. , Kumer J. B. , Mergenthaler J. L. , Waters J. W. , Gille J. C. , Yue G. K.
Published: February 2004

We present the first near‐global set of correlated measurements of stratospheric HCl and ClONO2 concentrations. These data, obtained from the Upper Atmosphere Research Satellite (UARS) between August 1992 and March 1993, are analyzed using the Goddard trajectory mapping technique. These data indicate that, between 20 and 30 km altitude and 60°N to 60°S latitude, total inorganic chlorine (Cly) is fairly evenly distributed between ClONO2 and HCl, with HCl the slightly more dominant reservoir. The sum of UARS measurements of HCl and nighttime ClONO2, which approximates Cly at these altitudes, closely agrees with Cly derived from a tracer‐Cly relation originally derived from aircraft data, increasing confidence in the UARS data. Comparisons between these data and two‐dimensional model results suggest that models underpredict ClONO2 (overpredict HCl) near 20 km and overpredict ClONO2 (underpredict HCl) near 30 km, although the 20‐km underprediction is not as large as analyses of aircraft measurements have indicated.
Can observations of postglacial rebound tell whether the rheology of the mantle is linear or nonlinear?
Authors: Wu Patrick
Published: February 2004

It has been argued that since a power‐law mantle may appear to the postglacial rebound process as linear if the rebound stress is less than the ambient tectonic stress, therefore, observations of rebound cannot be used to determine whether the flow law in the mantle is linear or nonlinear. The purpose of this paper is to show that this may not be completely true if the rebound process sees the steady‐state creep. It will be demonstrated that for sites near the centre of rebound, the relative sea level (RSL) observations cannot distinguish a Newtonian mantle from a Power‐law mantle with large ambient stress. However, for sites outside the ice margin, the RSL signature for a power‐law mantle is clearly distinguishable from that due to deep flow in a Newtonian mantle. This characteristic of power‐law medium is independent of the ambient stress level and is unlikely to change with more complicated rebound models. If these results remain valid in future work, then RSL data near the ice margin can be used to argue against a steady‐state power‐law mantle.
Implications of spatial and temporal development of the aftershock sequence for the Mw 8.3 June 9, 1994 Deep Bolivian Earthquake
Authors: Myers Stephen C. , Wallace Terry C. , Beck Susan L. , Silver Paul G. , Zandt George , Vandecar John , Minaya Estela
Published: February 2004

On June 9, 1994 the Mw 8.3 Bolivia earthquake (636 km depth) occurred in a region which had not experienced significant, deep seismicity for at least 30 years. The mainshock and aftershocks were recorded in Bolivia on the BANJO and SEDA broadband seismic arrays and on the San Calixto Network. We used the joint hypocenter determination method to determine the relative location of the aftershocks. We have identified no foreshocks and 89 aftershocks (m > 2.2) for the 20‐day period following the mainshock. The frequency of aftershock occurrence decreased rapidly, with only one or two aftershocks per day occuring after day two. The temporal decay of aftershock activity is similar to shallow aftershock sequences, but the number of aftershocks is two orders of magnitude less. Additionally, a mb ∼6, apparently triggered earthquake occurred just 10 minutes after the mainshock about 330 km east‐southeast of the mainshock at a depth of 671 km.

The aftershock sequence occurred north and east of the mainshock and extends to a depth of 665 km. The aftershocks define a slab striking N68°W and dipping 45°NE. The strike, dip, and location of the aftershock zone are consistent with this seismicity being confined within the downward extension of the subducted Nazca plate. The location and orientation of the aftershock sequence indicate that the subducted Nazca plate bends between the NNW striking zone of deep seismicity in western Brazil and the N‐S striking zone of seismicity in central Bolivia. A tear in the deep slab is not necessitated by the data. A subset of the aftershock hypocenters cluster along a subhorizontal plane near the depth of the mainshock, favoring a horizontal fault plane. The horizontal dimensions of the mainshock [Beck et al., this issue; Silver et al., 1995] and slab defined by the aftershocks are approximately equal, indicating that the mainshock ruptured through the slab.
UARS PSC, ClONO2, HCl, and ClO measurements in early winter: Additional verification of the paradigm for chlorine activation
Authors: Geller Marvin A. , Yudin Valery , Douglass A. R. , Waters J. W. , Elson L. S. , Roche A. E. , Russell J. M.
Published: February 2004

We present an example of observations within a single air mass of ClO, ClONO2, and HCl from the instruments on the UARS spacecraft. A three‐dimensional chemistry‐transport calculation for HCl is used to show that this air mass has been transported through regions cold enough for polar stratospheric cloud formation and chlorine activation through heterogeneous chemical reactions. These data, together with modeling of HCl with and without heterogeneous loss as a qualitative measure of polar processing, indicate directly the transformation of the reservoirs HCl and ClONO2 to reactive chlorine species.
Stability of the Rake during the 1992, Landers Earthquake. An indication for a small stress release?
Authors: Cotton Fabrice , Campillo Michel
Published: February 2004

We use the high quality data set of the Landers earthquake to study in detail the ability of strong motion inversions to resolve the rake during the rupture process. Initially, we constrain the rake to be constant on the fault. Several inversions with different rake values show that a pure strike slip gives the best fit to the data. In a second step, we have allowed the rake to vary spatially. Spatial rake variations are well resolved by the data and remain small; the data strongly constrain the earthquake to be a pure strike‐slip event with almost no variation of the rake. We assume that the direction of the slip vector is always close to the direction of the applied stress, which itself is the vector sum of the pre‐existing stress and the dynamic stress changes. The stability of the rake on a fault with a dynamical rupture process which is clearly heterogeneous suggests that the pre‐existing stress level is quite homogeneous and that it dominates over the dynamic stress changes.
Mid‐latitude Jovian aurora produced by the impact of comet Shoemaker‐Levy‐9
Authors: Hill T. W. , Dessler A. J.
Published: February 2004

We propose a theoretical interpretation of the mid‐latitude ultraviolet auroral emissions in Jupiter's atmosphere that were observed with the Hubble Space Telescope after the impact of comet Shoemaker‐Levy‐9 fragment K. The emissions were observed 47–57 minutes after the impact at a location ∼12° south of the (southern‐hemisphere) impact site and, with brighter intensity, at the magnetically conjugate site in the northern hemisphere. Consistent with these observations, we hypothesize that the aurora is driven by the atmospheric re‐entry of the impact plume. The infalling plume material, moving primarily southward, acts as a snowplow, driving a divergent pair of east‐west flow jets in the upper atmosphere. These jets drive polarization currents in the dynamo layer which are closed by Birkeland (magnetic field aligned) current sheets connecting to Pedersen currents in the conjugate northern ionosphere. We expect, by analogy with terrestrial aurora, that the upward Birkeland current sheets require magnetic‐field‐aligned electrostatic potential drops which in turn accelerate the primary electrons that are responsible for auroral excitation. Other SL‐9 fragments of similar size probably produced similar auroral emissions that were not observed, either because the viewing geometry was unfavorable or because uv observations were not made at those times.
Planetary waves in total ozone and their relation to Antarctic ozone depletion
Authors: Bodeker G. E. , Scourfield M. W. J.
Published: February 2004

Stanford and Ziemke [1993] have recently demonstrated the versatility of the Total Ozone Mapping Spectrometer (TOMS) data set in characterizing the behaviour of Rossby‐gravity waves. Similar analyses performed here are extended to relate interannual differences in Southern Hemisphere mid‐latitude wave activity to the severity of the Antarctic ozone depletion. Total ozone wave powers for wavenumber 1 to 6 have been calculated from TOMS distributions for each day from 1979 to 1992 and a mean measure of Antarctic ozone depletion has been determined for each year. After normalization with respect to stratospheric chlorine loading, interannual differences in the severity of the Antarctic ozone hole are anti‐correlated with total wave powers. Furthermore, wintertime mean wave power and polar stratospheric temperatures are well correlated and appear to lag the equatorial Quasi‐biennial Oscillation (QBO) by 1 year.
CO2 transfer at the air‐sea interface: Numerical tests of the dual‐tracer method
Authors: Phillips Leon F.
Published: February 2004

Gas‐water fluxes of CO2, O2, He, SF6 and NH3 have been calculated for conditions corresponding to the measurements of Liss et al [1981] for O2 exchange and of Smith and coworkers [Smith and Jones, 1986; Smith et al, 1991] for CO2 exchange. For each experimental run, the best value of surface temperature was selected by matching the calculated transfer velocity to the measured value for O2 or CO2, and fluxes of the other gases were then calculated for steady state, boundary layer, surface renewal and eddy diffusion models. The results indicate that the dual tracer method should work well for sparingly soluble gases under conditions where a surface renewal model applies, and moderately well under conditions where the boundary layer model is appropriate, but they leave open the question of when such models should apply.
Diurnal/semidiurnal oceanic tidal angular momentum: Topex/Poseidon Models in comparison with Earth's rotation rate
Authors: Chao Benjamin Fong , Ray Richard D. , Egbert Gary D.
Published: February 2004

The oceanic tidal angular momentum (OTAM) has been demonstrated to be the primary cause for the diurnal and semidiurnal variations in the Earth's rotational rate, or ΔUT1. Three ocean tide models derived from the Topex/Poseidon altimetry mission are employed to yield predictions of ΔUT1 for eight major diurnal/semidiurnal tides. The predictions are compared with geodetic determinations of ΔUT1 from the very‐long‐baseline interferometry data both for long‐term observations and during intensive campaigns. The agreement is good, with discrepancies typically within 2–3 µs. Systematic discrepancies observed for the well‐determined M2 tide clearly reveal the contribution of the Earth's spin libration.
The 9 June 94 Bolivian Deep Earthquake: An exceptional event in an extraordinary subduction zone
Authors: Kirby Stephen H. , Okal Emile A. , Engdahl E. Robert
Published: February 2004

We investigate the physical setting of the Bolivian shock based on the history of the subducting Nazca plate, intraslab seismicity, deep seismic moment release, and seismic tomography. South America has two broad regions of reverse arc curvature. Subduction constrained to this unique geometry produces slab kinking contortions that may cause unusual slab thickening as they sink to the bottom of the transition zone and encounter resistance to penetration into the lower mantle. Such contortions are observed at intermediate depths “upstream” from the slab source regions of both the great 1970 Colombian and 1994 Bolivian events. Thickening helps explain how the Nazca slab accommodates large seismic source dimensions at depths of 625–650 km.
Toroidal splitting observations from the Great 1994 Bolivia and Kuril Islands Earthquakes
Authors: Tromp Jeroen , Zanzerkia Eva
Published: February 2004

The June 9, 1994, Bolivia earthquake and the October 4, 1994, Kuril Islands earthquake provide a unique opportunity for a splitting analysis of the Earth's long‐period toroidal free oscillations. We present toroidal splitting observations for the 6 fundamental modes 0T4, 0T5, 0T6, 0T7, 0T8, and 0T9, and for the 5 first overtones 1T1, 1T2, 1T3, 1T4 and 1T6. The first identification of mode 1T1 is made possible by simultaneously fitting the multiplets 1T1 and 0T7. The observed splitting is reasonably well explained by current shear velocity models of the mantle. Our analysis yields new estimates of the center frequencies and quality factors of these 11 toroidal modes.
Anisotropy of magnetic susceptibility: Measurement schemes
Authors: Borradaile Graham John , Stupavsky Mike
Published: February 2004

The precision of AMS determination is enhanced by measuring susceptibility in directions with a uniform orientation distribution that include the four body diagonals. Some standard 10.5 cm³ samples with mean susceptibility < 100µSI possess too few “magnetic” grains for reliable petrofabric interpretation whatever the measurement strategy. We should only interpret their AMS if they pass fabric homogeneity tests.
ISEE 3 observations of plasmoids with flux rope magnectic topologies
Authors: Slavin J. A. , Owen C. J. , Kuznetsova M. M. , Hesse M.
Published: February 2004

This paper reports new evidence for the existence of plasmoids with force‐free flux rope magnetic topologies. Motivated by the fact that force‐free magnetic flux ropes have intense axial fields at their centers, the ISEE 3 observations have been searched for plasma sheet intervals in which the magnetic field intensity exceeds that in the lobes by ≥10% for a minute or longer. A total of 39 “high field regions” were found which met this simple criterion. Further examination showed that they nearly always correspond to the core regions of plasmoids; i.e, intervals of bipolar Bz with durations of minutes, fast tailward flows and clear substorm associations. A new, more realistic plasmoid magnetic field model which represents the core region as a non‐linear force‐free flux rope was developed and validated using these events. Finally, observations suggesting that plasmoids evolve toward quasi‐force‐free flux rope configurations as they move down the tail are presented.
New results on the site of initiation of coronal mass ejections
Authors: Eselevich Victor
Published: February 2004

In this paper it is shown that in some months of the phase of minimum solar activity 1985–1987 as many as (80–90)% of a total number of CMEs occur near belts of streamers with neutral line (NL), and only (10–20)% of them appear near belts of streamers without NL. (Streamers without NL separate regions in the corona with the same direction of radial fields of magnetic tubes originating from adjacent coronal holes). With increasing solar activity, the center of gravity of the number of emerging CMEs is shifting toward belts of streamers without NL and reaches over 80% of their total number in some months by the end of 1989. The CME position angle (PA) coincides, on average, with the angle of the portion of NL which straddles the CME. It is quite possible that this condition is satisfied not in the average but rigorously for each CME.
Formation of thin current sheets in a quasistatic magnetotail model
Authors: Wiegelmann T. , Schindler K.
Published: February 2004

Observations suggest that thin current sheets forming in the near‐Earth magnetotail late in substorm growth phases may be a crucial part of substorm evolution. In a simple theoretical model the current density was shown to become singular for suitable external perturbations. Here, we address the same problem in a more realistic model based on the adiabatic MHD ‐ theory developed by Schindler and Birn [1982]. We show that under suitable conditions the formation of a thin current sheet in the near‐Earth tail is an intrinsic aspect of flux transfer to the magnetotail. The mechanism is based on the strong variation of flux tube volume with the magnetic flux function.
Phase transitions in the Martian mantle and the generation of megaplumes
Authors: Zhou Hua , Breuer Doris , Yuen David A. , Spohn Tilman
Published: February 2004

The influences of two exothermic phase transitions, the olivine to β‐spinel and the β‐ to γ‐spinel transition, on Martian mantle convection have been studied with an axisymmetric spherical‐shell model. There are depth dependences in the thermal expansivity and gravity, which, taken together, decrease by a factor of between 2 to 3 across the mantle. We have discovered an unique mechanism for the amplification and superheating of megaplumes in Mars, which works particularly well because of the optimal heights of the two destabilizing exothermic phase transitions above the Martian core‐mantle boundary (CMB): The cold descending mantle flow is accelerated by its interactions with the phase transitions and the nearby CMB forces the flow to bend over sharply. Together these effects result in strong localized viscous heating, which will generate and accelerate a rising plume and may even cause melting in its deep interior and produce komatiites.
A broadband P wave analysis of the large deep Fiji Island and Bolivia Earthquakes of 1994
Authors: Goes Saskia , Ritsema Jeroen
Published: February 2004

The complex broadband P‐wave displacement recordings of the 570 km deep March 9, 1994, Mw 7.6 Fiji Island and the 660 km deep June 9, 1994, Mw 8.2 Bolivia earthquakes are analyzed to estimate the spatial and temporal characteristics of their ruptures. We model relative arrival times and amplitudes of coherent subevents in P waveforms, and perform waveform analyses. We resolve: (1) short rupture durations relative to their seismic moments, 12 and 40 s for the Fiji and Bolivia earthquakes, respectively; (2) small areas of main moment release, for both earthquakes 30 × 40 km²; (3) high stress drops compared to shallow earthquakes, with the stress drop of the Bolivia event (283 MPa) being significantly higher than the stress drop of the Fiji event (26 MPa); (4) small changes in mechanism (up to 10° changes in fault plane orientation); and (5) a steeply dipping rupture plane for the Fiji earthquake, and a shallowly dipping rupture plane for the Bolivia earthquake. Details of the ruptures are difficult to resolve using teleseismic P waveforms.
The tectosphere and postglacial rebound
Authors: Manga Michael , O'Connell Richard J.
Published: February 2004

Large lateral variations in the thickness of the lithosphere and viscosity of the mantle may be associated with continental roots. The effects of continental roots, or the tectosphere, on postglacial rebound are calculated using an axisymmetric flow model in which both the mantle and lithosphere are described as Newtonian fluids. Continental roots are shown to have a measurable effect on postglacial rebound, in particular, on the evolution of the peripheral bulge. Effects of continental roots are concentrated near the edge of the tectosphere, and thus often near ocean‐continent boundaries where many relative sea‐level histories are measured. The pattern and distribution of tectonic and seismic activity associated with deglaciation are affected by a tectosphere.
Inversion of the COPROD2 magnetotelluric data using a diffusive‐to‐propagative mapping (DPM)
Authors: Tournerie Benoît , Gibert Dominique , Virieux Jean
Published: February 2004

Diffusive‐to‐Propagative Mapping (DPM) transforms a diffusive electromagnetic field into a dual wave field to produce electromagnetic reflectivity images similar to non‐migrated seismic sections. An application of DPM to the COPROD2 data set gives reflectivity images showing three distinct reflectors attributed to resistivity jumps located at depths ranging from 2 to 50 km. The deeper reflector may be related to a major west‐dipping seismic reflector detected with the COCORP seismic data.
Springtime reduction in MF mesospheric echo occurrence
Authors: Jones G. O. L. , Jarvis M. J.
Published: February 2004

Radar echoes from the upper mesosphere recorded by the dynasonde at Halley (76°S, 27°W), Antarctica, over four years have been studied to reveal the diurnal and seasonal characteristics of echo occurrence. In addition to the expected daily variation, a distinct seasonal change in the number and altitude of the echoes is apparent. The prevalence of echoes during the winter months is followed, in all four years studied, by a period during the Antarctic spring when echo occurrence falls markedly for a period lasting for about three weeks. This dearth of echoes coincides with the breakdown of the polar vortex circulation pattern in the lower atmosphere providing strong evidence of the neutral dynamical coupling between the stratosphere and mesosphere.
Climatic implications of δ13C variations in a Japanese cedar (Cryptomeria japonica) during the last two millenia
Authors: Kitagawa Hiroyuki , Matsumoto Eiji
Published: February 2004

Tree‐ring δ13C of both modern Japanese cedars, and of a giant Japanese cedar growing throughout the last two millennia on Yakushima Island, southern Japan, were studied. δ13C of eleven modern trees from 320 m to 1700 m above mean sea level revealed a strong dependency on tree growth‐elevation and a decreasing trend from the late 19th century to the present. Changes in both climate and δ13C of atmospheric CO2 appear to be important for these changes. Assuming temperature change to be a dominant factor influencing δ13C‐growth elevation relationship, we have inferred a temperature dependency of δ13C, −0.29±0.02‰ °C−1 for Japanese cedar. Applying this relationship to a decadal‐δ13C time series of a giant Japanese cedar, we reconstructed a high‐resolution climatic record for the last two millennia. A maximum‐entropy spectral analysis of the tree‐ring δ13C time series revealed a resemblance of that of other climatic proxy, and the presence of the well‐known periodicity (ca 90 and near 200 years), characteristic of tree‐ring Δ14C, governed by solar modulation of galactic cosmic rays. Supporting evidence for a Sun‐climate relationship was presented.
Greenland Ice Sheet thickness changes measured by laser altimetry
Authors: Krabill W. , Thomas R. , Jezek K. , Kuivinen K. , Manizade S.
Published: February 2004

Precise airborne laser‐altimetry surveys, at locations on the Greenland ice sheet, that had been accurately surveyed in 1980 and 1981, reveal a thickening in western Greenland of up to two meters between 1980 and 1993. We cannot yet state whether this represents a long‐term trend or the cumulative effects of interannual variability of snow‐accumulation rates. Nevertheless, the information presented here provides an indication of ice‐thickness changes across southern Greenland in unprecedented detail. Laser altimetery surveys have now been made over all the major ice sheet drainage basins, and will be repeated at regular intervals to provide detailed estimates of ice thickening/thinning rates over the entire ice sheet.
High resolution remote sensing of sulfate aerosols from CO2 lidar backscatter
Authors: Srivastava V. , Bowdle D. A. , Jarzembski M. A. , Rothermel J. , Chambers D. M. , Cutten D. R.
Published: February 2004

A high resolution technique for remotely sensing aerosol sulfate composition has been developed, based on the ratio of aerosol backscatter measured at 9.1 and 10.6 µm wavelengths with two continuous wave CO2 lidars. This is demontrated using data from the NASA GLObal Backscatter Experiment (GLOBE) over the Pacific Ocean in 1990. Results indicate changes from sulfuric acid with some ammoniation in clean conditions and presence of dust with ammoniated sulfates in continental plumes. Lidars provide good estimates of backscatter ratio with ∼5 second sample times (∼1 km spatial resolution) in aerosol concentrations as low as ∼10−2 µg/m³.
A reinterpretation of the data from the NASA Stratosphere‐Troposphere Exchange Project
Authors: Newman Paul A. , Schoeberl Mark R.
Published: February 2004

Data obtained during the NASA Stratosphere Troposphere Exchange Project (STEP) Mid‐Latitude Field Experiment displayed laminae of ozone, water, and condensation nuclei in the stratosphere in association with a mid‐latitude stratosphere‐troposphere folding event. Danielsen et al. (1991) constructed cross sections of these observations, and interpreted these quasi‐horizontal laminae as evidence of ultra‐low frequency gravity waves. We use a new technique to show that these laminae could have resulted from differential advection, rather than transport by ultra‐low frequency gravity waves. This new technique uses reverse domain filling back trajectories on multiple isentropic surfaces in conjunction with modified potential vorticity to reveal the qualitative details of the constituent laminae.
Sources of shocks and compressions in the high‐latitude solar wind: Ulysses
Authors: Phillips J. L. , Goldstein B. E. , Gosling J. T. , Hammond C. M. , Hoeksema J. T. , McComas D. J.
Published: February 2004

During its southern transit Ulysses sampled the solar wind to −80.2° latitude. Slow streamer belt wind was seen only equatorward of −35°, but its influence extended to much higher latitudes. Reverse shocks bounding the equatorial CIR were seen as far south as −58.2°. High‐latitude compressional waves showed no clear correlation with that CIR. Speed and density patterns show that solar rotational modulation persisted up to 25° poleward of the slow wind. Compressional structures at highest latitudes were probably driven by spatial or temporal variations within the southern coronal hole.
A very broadband study of the 1994 Deep Bolivia Earthquake Sequence
Authors: Wu Jun , Wallace Terry , Beck Susan
Published: February 2004

We have examined the source process of the June 9, 1994 Bolivia earthquake in the period range of body waves to free oscillations. A series of moment tensor inversions were performed on various teleseismic wave types and frequency bands to infer the source parameters and to map the temporal character of the source process. Time independent moment tensor inversion of the body waves (P and SH) yields a source time function of 46 seconds duration with four major “pulses” of moment release, with moment release dominated by the third pulse. The focal mechanism is dominantly dip‐slip on the sub‐horizontal nodal plane (strike 287°, dip 8° and slip −74°). The best bodywave fit requires a non‐double‐couple component of approximately 7%; although this could be due to an isotropic component of the source, it is at the margin of resolution. Time dependent moment tensor inversion of the body waves, which yields independent time histories for each moment tensor element, shows that the source orientations (fault plane and slip direction) change very little throughout the rupture duration. Analysis at several frequencies shows that the seismic moment is very stable (3.0 × 1021 Nm ± 6%) at periods greater than 150 seconds and that the isotropic moment is negligible given the resolution.

We also modeled the P‐waves for the January 10, 1994 event, the strong aftershock of June 9, 1994 and the August 8, 1994 earthquake. Rotation of the P axes for events after the mainshock may suggest a possible stress adjustment.
Comet Shoemaker‐Levy 9: Fragment and progenitor impact energy
Authors: Takata Toshiko , Ahrens Thomas J. , Harris Alan W.
Published: February 2004

Initial observational data from the impact of fragments of Comet Shoemaker‐Levy 9 (SL9) are compared with smoothed particle hydrodynamic (SPH) calculations to determine their pre‐impact diameters and the equivalent diameter of the SL9 progenitor. Diameters (solid ice) of 2.0±0.1, 2.0±0.05, 2.1±0.04 and 1.9±0.05 km for fragments A, E, G1, and W are obtained from impact‐induced plume heights from the Hubble Space Telescope (HST) data. Applying these values to scale apparent diameters for the balance of 18 SL fragments in Weaver et al.'s [1995] catalog of 22 objects yields a SL9 progenitor diameter of 5.0±1.8 km. This corresponds to total impact energy of 1.2 (+1.8−0.8) × 1030 erg. Such an energetic event occurs on Jupiter and Earth at least every 4,900 +4,700, −2,700, and ∼0.5 × 108 years, respectively.
Present‐day post‐glacial sea level change far from the Late Pleistocene ice sheets: Implications for recent analyses of tide gauge records
Authors: Mitrovica Jerry X. , Davis James L.
Published: February 2004

We examine the sensitivity of predictions of the present‐day rate of sea level change due to glacial isostatic adjustment (GIA) in two regions located within the ‘far‐field’ of the Late Pleistocene ice sheets (Europe/north Africa and the western Pacific/Caribbean) to variations in the mantle viscosity profile. The regions considered here encompass the location of 11 (of 21) sites used in a recent determination, based on GIA‐corrected tide gauge records, of the global rate of secular sea level change. Our analysis suggests that the mean GIA correction at the 11 far‐field sites may vary by as much as 0.5 mm/yr, depending on the adopted Earth model, and we derive a bound on the (residual) secular sea level rise of 1.1 to 1.6 mm/yr. This bound is consistent with our analysis of the tide gauge record from the U.S. east coast, and it suggests that previous estimates of the residual sea level rise represent an upper bound.
Observation of the two‐day wave near the southern summer stratopause
Authors: Limpasuvan Varavut , Leovy Conway B.
Published: February 2004

Temperature and H2O measurements from the Upper Atmospheric Research Satellite Microwave Limb Sounder (UARS MLS) data sets during southern hemisphere summer of 1991–92 are analyzed using the asynoptic mapping method. Results show a prominent wavenumber 3 two‐day wave confined to latitudes between 60°S and 4°N and to altitudes above 2 hPa. The temperature wave amplitude increases upward to the upper limit of the observations and maximizes at 2.0 K near 0.465 hPa. The H2O wave amplitude reaches a maximum of 0.25 ppmv near 1 hPa. Evidence suggestive of wave breaking and meridional mixing associated with the interaction between this wave and a lower frequency wavenumber 1 is shown.
GEOTAIL observations on the reconnection process in the distant tail in geomagnetically active times
Authors: Nishida A. , Mukai T. , Yamamoto T. , Saito Y. , Kokubun S.
Published: February 2004

A statistical study is made on the reconnection process in the distant tail by using the GEOTAIL observations at x≈ −150 Re and −95 Re in geomagnetically active times with Kp≥3. Occurrence frequencies of various combinations of the field polarity and the convection direction suggest that at least 75% of the reconnection of open field lines occurs inside 150 Re and at least 39% occurs inside 95 Re. At 150 Re the convection of closed field lines constituting the viscous‐like cell is at most 25% of the convection generated by the reconnection of open field lines. The reconnection rate of open field lines varies across the tail and is a few times higher near the tail axis than at the flanks.
Atmospheric limitations to repeat‐track radar interferometry
Authors: Goldstein Richard
Published: February 2004

In its recent radar imaging mission, the Shuttle Imaging Radar satellite (SIR‐C) devoted three days to repeat‐track interferometry. We have analyzed the data from a test site in the Mojave desert of California. Although good topography (±10 m on 21 m postings) was obtained, most of the error was caused by turbulent water vapor in the lower atmosphere. Spatial structure of 6 km and all smaller sizes was observed. The RMS, one‐way time delay was found to be 0.24 cm. Essentially identical results were obtained at two wavelengths, 24 and 5.7 cm.
Role of Fermi acceleration in explosive enhancement of cross‐tail current in late substorm growth phase
Authors: Ganguli G. , Palmadesso P. J. , Fedder J. , Lui A. T. Y.
Published: February 2004

During the substorm growth phase, thinning of the plasma sheet can energize the unmagnetized ions trapped within it via a Fermi acceleration process. We show here that the energy growth rate, affecting mostly the unmagnetized ions, is exponential in time. The Fermi acceleration will give rise to a large enhancement in the cross‐tail ion current density and would be most prominent during the late growth phase. This prediction is quite consistent with previously reported satellite observations which show that the cross‐tail current density intensifies rapidly during the final stage of the growth phase just prior to current disruption.