bluuebunny/crossref_metadata_2025 huggingface dataset:
Variations of noble gas abundances and isotope ratios in a single MORB pillow
Authors: Kumagai Hidenori , Kaneoka Ichiro
Published: February 2004

To evaluate variations of noble gas signatures within a single MORB pillow caused at its extrusion, all noble gas abundances and isotope ratios (from He to Xe) were analyzed in different portions of a pillow basalt from the glassy rim to the interior by slicing off at every 2.5mm in thickness (#1 to #7). 40Ar/36Ar and He contents are high in glassy parts, and rapidly decrease toward the inner crystallized parts. Although ³He/4He is almost uniform among glassy parts (#1 to #3), the outermost part (#1) has a lower 40Ar/36Ar than the inner glassy parts (#2 and #3). This indicates incorporation of low 40Ar/36Ar component into the glassy rim from the surrounding materials at its solidification. Abundances of heavier noble gases, especially Xe, greatly increase toward crystallized parts. It could not be explained by incorporation of surrounding noble gases dissolved in the seawater and requires some other component such as fractionated product during crystallization by solid‐melt partition or derived from fine sediments. In order to obtain magmatic signature, outermost glassy part should be eliminated as well as crystalline parts.
Mars: Northern hemisphere slopes and slope distributions
Authors: Aharonson Oded , Zuber Maria T. , Neumann Gregory A. , Head James W.
Published: February 2004

We investigate slope distributions in the northern hemisphere of Mars from topographic profiles collected by the Mars Orbiter Laser Altimeter. Analysis of the region from about 12°S to 82°N, over diverse geologic units, indicates that the range of regional‐scale slopes is small, generally <3°. Surface smoothness is most distinctive in the vast northern hemisphere plains, where slopes are typically <1°. Amazonis Planitia is particularly remarkable in its smoothness, exhibiting an rms variation in topography of <2 m over a 100‐km baseline. This relative smoothness is still present when compared with other sampled areas of the Martian northern hemisphere and with volcanically resurfaced terrains elsewhere in the solar system. Planetary surfaces of large areal extent that are most comparable to Amazonis in terms of rms elevation variation over long baselines are depositional in origin and include terrestrial oceanic abyssal plains and certain sedimentary basins. Slopes across the Valles Marineris canyon system show that the upper portion of the walls are significantly and consistently steeper than the lower walls, characteristic of extensive mass wasting. The observed long‐runout is consistent with a high‐energy collapsed flow. In the neighboring Noctis Labyrinthus canyons the duality between the upper and lower walls is reduced, and indicates a lower energy modificational history and/or greater cohesion of wall rock.
Nitric acid scavenging by mineral and biomass burning aerosols
Authors: Tabazadeh A. , Jacobson M. Z. , Singh H. B. , Toon O. B. , Lin J. S. , Chatfield R. B. , Thakur A. N. , Talbot R. W. , Dibb J. E.
Published: February 2004

The abundance of gas phase nitric acid in the upper troposphere is overestimated by global chemistry‐transport models, especially during the spring and summer seasons. Recent aircraft data obtained over the central US show that mineral aerosols were abundant in the upper troposphere during spring. Chemical reactions on mineral dust may provide an important sink for nitric acid. In regions where the mineral dust abundance is low in the upper troposphere similar HNO3 removal processes may occur on biomass burning aerosols. We propose that mineral and biomass burning aerosols may provide an important global sink for gas phase nitric acid, particularly during spring and summer when aerosol composition in the upper troposphere may be greatly affected by dust storms from east Asia or tropical biomass burning plumes.
An observational constraint on the strength of the toroidal magnetic field at the CMB by time variation of submarine cable voltages
Authors: Shimizu Hisayoshi , Koyama Takao , Utada Hisashi
Published: February 2004

Electric potential difference observed by using submarine cables contains various kinds of geophysical information. In this paper, we attempt to constrain the strength of the toroidal magnetic field at the CMB by comparing the time‐dependent part of cable voltages and EM responses by a forward modeling. Assuming the linear‐trend of the observed electric potential reflects thirty‐year period variation, which is taken as a reference time‐scale for the variation, of the magnetic field at the CMB, the toroidal field strength at the CMB is estimated to be about 1–100 times that of the poloidal magnetic field there. The values should be considered as approximate upper bounds of the toroidal field variation because of short data length analyzed. Accumulation of a longer time series will lead to more accurate estimation of amplitude of time variations which enables us to give more definite constraints on the behavior of the toroidal field.
Seismic attenuation of the inner core: Viscoelastic or stratigraphic?
Authors: Cormier Vernon F. , Xu Li , Choy George L.
Published: February 2004

Broadband velocity waveforms of PKIKP in the distance range 150° to 180° are inverted for inner core attenuation. A mean Qα of 244 is determined at 1 Hz from 8 polar and 9 equatorial paths. The scatter in measured Q−1 exceeds individual error estimates, suggesting significant variation in attenuation with path. These results are interpreted by (1) viscoelasticity, in which the relaxation spectrum has a low‐frequency corner near or slightly above the frequency band of short‐period body waves, and by (2) stratigraphic (scattering) attenuation, in which attenuation and pulse broadening are caused by the interference of scattered multiples in a velocity structure having rapid fluctuations along a PKIKP path. In the scattering interpretation, PKIKP attenuation is only weakly affected by the intrinsic shear attenuation measured in the free‐oscillation band. Instead, its frequency dependence, path variations, and fluctuations are all explained by scattering attenuation in a heterogeneous fabric resulting from solidification texturing of intrinsically anisotropic iron. The requisite fabric may consist of either single or ordered groups of crystals with P velocity differences of at least 5% and as much as 12% between two crystallographic axes at scale lengths of 0.5 to 2 km in the direction parallel to the axis of rotation and longer in the cylindrically radial direction, perpendicular to the axis of rotation.
“Implicit ice” in the global theory of glacial isostatic adjustment
Authors: Peltier W. R.
Published: February 2004

The inference of ice sheet paleo‐topography with respect to sea level is herein shown to require accounting for an accurately calculable additional ice mass beyond that which is explicitly required as input to the integral equation for relative sea level history.
Arctic sea ice extent and melt onset from NSCAT observations
Authors: Yueh Simon H. , Kwok Ronald
Published: February 2004

NSCAT Ku‐band microwave observations of the Arctic sea ice cover are described on their potential use for estimating ice extent and timing of spring melt. A simple comparative analysis of the NSCAT Arctic sea ice extent and high‐resolution Radarsat imagery suggests that the SSM/I 25% ice concentration contour appears to be a good indicator of the winter Arctic ice edge. For spring melt‐onset, a comparative study of NSCAT sea ice observations and NCEP/NCAR surface air temperature indicates that Ku‐band backscatter of the snow cover over multiyear ice has a clear and steep change as the surface air temperature rises above freezing. This signature of melt onset should provide useful large‐scale estimates of the dates of melt onset with spaceborne scatterometer data. A more extensive validation of the potential of this dataset is suggested.
The relationship between MOLA northern hemisphere topography and the 6.1‐Mbar atmospheric pressure surface of Mars
Authors: Smith David E. , Zuber Maria T.
Published: February 2004

To assist in targeting of landers and to enable comparison of new elevation data to previous topography models, we have re‐determined the position of the 6.1‐mbar atmospheric pressure surface on Mars with respect to surface topography from the Mars Orbiter Laser Altimeter (MOLA). The 6.1‐mbar surface lies, on average, 1600 m below the geoid‐defined zero level of MOLA topography, which occurs at an average pressure of 5.2 mbars at LS=0°. The elevation of the 6.1‐mbar surface is expected to vary by 1.5–2.5 km over the Martian year due to the seasonal exchange of CO2 between the atmosphere and polar caps. For average Martian atmospheric conditions, the pressure at the Mars Surveyor ‘98 landing site is expected to be ∼5.0 mbars during the lander science phase of the mission assuming an elevation of 1600 meters above the zero level defined by MOLA topography.
Estimates of turbulent energy dissipation rates from determinations of characteristic vertical wavenumber by EISCAT
Authors: Hall C. M. , Hoppe U.‐P.
Published: February 2004

By measuring the vertical component of velocity in the height range 74–90 km above Tromsø (69°N, 19°), with a 1 km height resolution, we are able to estimate characteristic wavenumbers, m*. In turn, using well‐established theory, these m* may be interpreted in terms of wave energy and an upper limit of the energy dissipation rate, ε. The time‐variation of ε derived in this way is in general agreement with other radar, model and in situ results. These estimates, although now available with good seasonal coverage, are nevertheless for a limited height range only. In order to overcome this restriction to some degree, the results are combined with a season and height dependent model of the eddy diffusion coefficient, K to generate a picture of the seasonal variability of energy dissipation in the height regime 60–90km.
Perturbation to global tropospheric oxidizing capacity due to latitudinal redistribution of surface sources of NOx, CH4 and CO
Authors: Gupta Mohan L. , Cicerone Ralph J. , Elliott Scott
Published: February 2004

Economic and social projections indicate that during next several decades there will be major geographical redistribution of surface emissions of O3 precursors, such as NOx, CH4 and CO. A net decrease in their emissions from northern hemispheric mid‐latitudes will be accompanied by substantial increases from the tropics. We have investigated a hypothetical scenario of currently underway transition of such emission patterns using a global two‐dimensional photochemical model. With overall O3 precursor releases held constant, a simultaneous transfer of their emissions by 25% from the latitude belt 75°N–35°N to 5°S–35°N increases tropospheric oxidizing capacity such that the methane global lifetime and concentrations fall by more than 3%. Seasonally dependent changes in surface O3 concentrations are also calculated. In influencing OH concentration, redistribution of surface NOx emissions is 2–3 orders of magnitude more efficient per unit mass than CO emissions. Shifts in methane sources have insignificant effects on global photochemistry, but lead to a decrease in its interhemispheric gradient.
Depth variation of the crustal structure of the subducting plate along the Nankai Trough, off Kii Channel, Japan
Authors: Sato Toshinori , Mochizuki Kimihiro , Kasahara Junzo , Fujie Gou , Nishisaka Hiromasa , Koresawa Sadayuki
Published: February 2004

A seismic refraction‐reflection experiment using ocean bottom seismometers with artificial sources comprising airguns and explosions was conducted at off Kii Channel, the Nankai Trough, where interplate earthquakes occurred periodically. Using P‐wave travel time analyses including non‐linear travel time inversion, the depth variation of the crustal structure along the Nankai Trough was revealed. The results show that the subducting depth of the Philippine Sea plate changes at off Kii Channel. The plate is subducting at a shallow location at the west side and at a deep location at the east side. The depth of the plate boundary is about 8 km at the west side and about 9 km at the east side. This result and former studies indicate that the variation of subducting depth exists beneath Kii Channel and off Kii Channel regions. This depth change of the plate boundary might affect the process of interplate earthquake occurrence.
Mantle degassing of major and minor volatile elements during the Earth's history
Authors: Tajika Eiichi
Published: February 2004

Total amounts of major and minor volatile elements (H2O, C, S, N, F, Cl, Br, ³He, 36Ar, 40Ar, and 20Ne) degassed from the mantle throughout the Earth's history are estimated based on the present‐day mantle degassing rates and on the results of the 40Ar degassing model coupled with models of thermal evolution of the mantle and magma generation at midocean ridges. Relative contribution of continuous degassing due to volcanism throughout the Earth's history to the abundance of each volatile element in the surface reservoirs at present are obtained. The results suggest that, although both early and continuous degassing processes (and/or a late accretionary veneer) might have influenced all these volatile histories, contribution of each process seems to be very different for each volatile, probably because of differences in solubility into silicate melt, partition coefficient between liquid and solid phases, and efficiency of recycling into the mantle.
Dynamics of the aurora and associated convection currents during a cusp bifurcation event
Authors: Sandholt P. E. , Farrugia C. J. , Moen J. , Cowley S. W. H. , Lybekk B.
Published: February 2004

We report the detailed two‐dimensional evolution of a transient auroral bifurcation in the cusp region which occurred during an interval of eastward (By>0) oriented interplanetary magnetic field (IMF). The actual auroral bifurcation is characterized by the near‐simultaneous activation and intensification of two latitudinally separated auroral forms which both expanded westward across the 1200 MLT meridian, after their initial appearance in the postnoon sector. The northernmost form (called type 2) is typical of periods of northward IMF orientation while the southernmost form (called type 1) represents a continuation and intensification of a type of auroral activity which is characteristic of intervals of southward IMF orientation. The auroral bifurcation is commonly observed when the IMF is in an intermediate regime of clock angles (∼45°–90°), i.e., when By is the dominating IMF component. We explain the transient cusp bifurcation in terms of a short‐lived activation of high‐latitude reconnection and an associated lobe cell convection/current system and type 2 aurora embedded in a long interval of active low‐latitude reconnection/type 1 aurora.
Equatorial F region zonal plasma irregularity drifts under magnetospheric disturbances
Authors: Abdu M. A. , Jayachandran P. T. , MacDougall J. , Cecile J. F. , Sobral J. H. A.
Published: February 2004

Equatorial F region plasma drift velocities measured by a digital ionosonde (CADI) that was recently installed in Fortaleza, Brazil, are used to investigate magnetospheric disturbance effects in the vertical (zonal) and zonal (vertical) velocities (electric fields). For the first time we report evidence of large fluctuations in irregularity zonal drift velocities (∼50–180 m/s) associated with magnetospheric disturbances. The fluctuations in the zonal velocity, anti correlated with those in vertical velocity, are unlikely to be produced by prompt penetration of disturbance meridional electric field of high latitude/magnetospheric origin. A mechanism is proposed to explain the velocity fluctuations that involves: (1) Hall polarization vertical electric field in the E‐layer that is field line mapped on to F‐layer, and (2) electric field caused by vertical current arising from divergence in field line integrated zonal Pedersen current; both produced by the primary disturbance zonal electric field. Enhanced nighttime E region conductivity with possible spatial gradients, a requirement for the functioning of this mechanism, is observed to be present from other simultaneous measurements, whose source is suggested to be particle induced ionization in the south Atlantic Magnetic Anomaly (SAMA) zone, as known also from previous studies.
On the relationship of aerosol optics to moments of particle size distribution
Authors: de P. Vasconcelos Luis A. , Macias Edward S. , White Warren H.
Published: February 2004

Particle size distributions are sometimes conveniently described in terms of their integral moments. It is known that the details of a size distribution cannot always be recovered from its moments, but it has also been shown that an aerosol's optical properties can be insensitive to these details. This paper explores the limits of the correspondence between optics and moments, exhibiting size distributions with identical moments but dissimilar optical properties, and dissimilar moments but similar optical properties. The examples involve multimodal size distributions of the type observed in continental ambient air.
Diabatic subsidence in the subtropical upper troposphere derived from SAGE II measurements
Authors: Lin W. Y. , Zhang M. H. , Geller M. A.
Published: February 2004

Composite diabatic subsidence rates in the subtropical upper troposphere are derived using water vapor measurements of high vertical resolution from SAGE II in conjunction with collocated ECMWF reanalysis. Their relationship with the concentration of upper tropospheric water vapor is examined. The mean vertical profiles of subsidence rate show a monotonic increase in downward mass flux from the tropopause down to at least 400 mb reaching a magnitude of 22 mb day−1. This vertical structure of subsidence suggests horizontal mass convergence and horizontal moisture transport at all levels above 400 mb. Seasonal variation of upper tropospheric subsidence is also presented.
Geotail observations of north‐south plasma velocity enhancements in the lobe near substorm expansion phase onset
Authors: Taguchi S. , Kiyohara M. , Mukai T. , Yamamoto T. , Nose M. , Saito Y. , Kokubun S.
Published: February 2004

This paper reports on the enhancement of the lobe plasma velocity towards the neutral sheet. Analyzing the Geotail plasma and magnetic field data in the lobes earthward of X = −45 RE, we identified 30 events of several‐minute magnetic field increase‐and‐decrease during which the field tilts only southward; that is, the BZ variation is unipolar. For most of these events, we found that the lobe plasma velocity towards the neutral sheet is enhanced and peaked around the most southward tilting of the field. The average of the peak magnitude is about 130 km/s in a plane perpendicular to the magnetic field. For each case, this magnitude is roughly 1–10 % of the lobe Alfven speed. We interpret the velocity enhancement having these characteristics as signatures of the transition from plasma sheet reconnection to lobe reconnection at the near‐Earth neutral line.
Hot oxygen corona at Europa
Authors: Nagy Andrew F. , Kim Jhoon , Cravens Thomas E. , Kliore Arvydas J.
Published: February 2004

A model of the hot oxygen exosphere at Europa was constructed. The source term for the hot atoms was assumed to be dissociative recombination of O2+ and Liouville's theorem was used to calculate their altitude distribution. It was found that near the surface the hot oxygen density is in excess of 200 cm−3, dropping to a value on the order of 50 cm−3 at 1500 km. These calculations indicate that the hot atomic oxygen densities are considerably less than the thermal molecular oxygen ones, but slightly larger than the measured sodium values. The escape flux of the hot oxygen atoms was calculated to be on the order of 1.4×108 atoms cm−2 sec−1. This corresponds to a global escape rate of 4.4×1025 atoms sec−1, which is more than an order of magnitude less than the estimated atmospheric sputtering rate.
Estimates of ice thickness in the Conamara Chaos Region of Europa
Authors: Williams Kevin K. , Greeley Ronald
Published: February 2004

Europa, the second Galilean moon outward from Jupiter, is similar in size to Earth's moon but has an outer water‐ice layer on the order of 100 km thick. Images acquired by the Galileo spacecraft reveal domical features and iceberg‐like blocks in some areas that suggest the ice was regionally thin at the time the features formed. This paper applies buoyancy and flexural models to some of the features to estimate ice thickness. Assuming that the ice blocks were floating in a liquid sublayer, the buoyancy model suggests an ice layer 0.2–3.0 km thick. Also, the flexural models suggest that only the upper 0.1–0.5 km of that ice layer responded elastically to stresses, acting as an elastic lithosphere.
Doubled CO2 effects on NOy in a coupled 2D model
Authors: Rosenfield Joan E. , Douglass Anne R.
Published: February 2004

Stratospheric NOy fields calculated using a zonally averaged interactive chemistry‐radiation‐dynamics model show significant sensitivity to the model CO2. Modeled upper stratospheric NOy decreases by about 15% in response to CO2 doubling, mainly due to the temperature decrease calculated to result from increased CO2 cooling. The abundance of atomic nitrogen, N, increases because the rate of the strongly temperature dependent reaction N + O2 → NO + O decreases at lower temperatures. Increased N leads to an increase in the loss of NOy which is controlled by the reaction N + NO → N2 + O. The decrease in NOy due to the lowered temperatures is partially compensated by changes in the residual circulation. In addition, the NOy reduction is shown to be sensitive to the NO photolysis rate.
Mantle viscosity inferences from joint inversions of pleistocene deglaciatio‐induced changes in geopotential with a new SLR analysis and polar wander
Authors: Vermeersen L. L. A. , Sabadini R. , Devoti R. , Luceri V. , Rutigliano P. , Sciarretta C. , Bianco G.
Published: February 2004

Joint inversions of post‐glacial rebound‐induced secular changes in low degree harmonics of the geopotential and true polar wander (TPW) systematically indicate that the upper mantle viscosity has a value that is considerably smaller than 1021 Pas. The lower mantle viscosity is about one order of magnitude larger than the upper mantle viscosity. Discrepancies in the viscosity profiles inferred from even and odd zonals are likely an indication of recent, unmodeled glacial forcings and/or insufficient precision in the evaluation of the mass loss from Pleistocene ice sheets. The influence of systematic errors in SLR data reduction due to thermal drag on the LAGEOS satellites for the uneven zonals of the geopotential is avoided by making use of the Starlette and Stella satellites to recover the uneven zonals and by considering lumped coefficients for these uneven terms.
Assimilation of MLS ozone measurements in the global three‐dimensional chemistry transport model ROSE
Authors: Levelt P. F. , Khattatov B. V. , Gille J. C. , Brasseur G. P. , Tie X. X. , Waters J. W.
Published: February 2004

A method for assimilating observations of ozone was implemented in the three‐dimensional global stratospheric chemistry transport model ROSE. The model contains an extensive photochemical scheme which includes heterogeneous chemistry and uses temperature and wind fields from the UKMO (United Kingdom Meteorological Office) stratospheric analysis.

Ozone measurements obtained by the Microwave Limb Sounder (MLS) on board the Upper Atmosphere Research Satellite (UARS) were assimilated in the model using the sequential statistical interpolation approach. The analysis is performed using a time invariant background error covariance matrix that only includes horizontal covariances. Results from a sixty day simulation are presented and it is shown that assimilation of the MLS observations results in improved global three‐dimensional distributions of ozone as seen from comparisons with MLS data not assimilated in the model. For further validation, the stratospheric total ozone fields computed from the analysis are compared with the TOVS total ozone measurements and it is shown that they agree within the uncertainty of the data.
Laminae in the tropical middle stratosphere: Origin and age estimation
Authors: Jost H. , Loewenstein M. , Pfister L. , Margitan J. J. , Chang A. Y. , Salawitch R. J. , Michelsen H. A.
Published: February 2004

In situ measurements of N2O and O3 aboard the Observations from the Middle Stratosphere (OMS) balloon payload in the tropics are presented. In November 1997 at 7°S very distinct laminated structures in the N2O profile were observed in contrast to earlier studies based solely on O3 profiles. The laminae probably are an observation of Rossby wave‐breaking events that lead to transport of mid‐latitude air into the tropics. Using a photochemical model of the ozone response within those air parcels, their residence time in the tropics is estimated to be 4 to 6 weeks. In February 1997 at 7°S a similar vertical profile of N2O revealed no mid‐latitude laminae. We present dynamical arguments to support the existence of such laminae in November, but not in February.
Comment on « Diffusion of HNO3 in ice »
Authors: Dominé Florent , Thibert Emmanuel
Published: February 2004

Sommerfeld et al. (1998) (hereafter: SKL) attempted to measure HNO3 diffusion in ice. Although they used HNO3 partial pressures much higher than atmospheric, they encountered contamination problems, and conclude that they could not obtain meaningful values of the diffusion coefficient of HNO3 in ice. In earlier measurements, we used a method having some similarities with theirs (Dominé and Thibert, 1995). SKL suggest that our data may have been affected by contamination. Here we examine their methods, find many differences with ours, and demonstrate that our data was not affected by contamination. We point out questionable choices in their experimental procedure, and in the earlier work of Diehl et al. (1995) and discuss the difference between their solubility data and ours. We propose changes to the procedure of SKL, so that an independent set of reliable data can be obtained on the diffusion and solubility of HNO3 in ice.
The Sun's total irradiance: Cycles, trends and related climate change uncertainties since 1976
Authors: Fröhlich Claus , Lean Judith
Published: February 2004

A composite record of the Sun's total irradiance compiled from measurements made by five independent space‐based radiometers since 1978 exhibits a prominent 11‐year cycle with similar levels during 1986 and 1996, the two most recent minimum epochs of solar activity. This finding contradicts recent assertions of a 0.04% irradiance increase from the 1986 to 1996 solar minima and suggests that solar radiative output trends contributed little of the 0.2°C increase in the global mean surface temperature in the past decade. Nor does our 18‐year composite irradiance record support a recent upward irradiance trend inferred from solar cycle length, a parameter used to imply a close linkage in the present century between solar variability and climate change.
On auroral ion conics and electron beams acceleration
Authors: Mishin Evgeny , Banaszkiewicz Marek
Published: February 2004

The results of a numerical simulation of the O+ energization perpendicular to the magnetic field (B) in “electrostatic shocks” with converging or diverging fields at altitudes ∼2000 km are presented. It is shown that non‐adiabatic motion in diverging “shocks” leads to the formation of coherent perpendicular O+ beams, whereas converging fields produce non‐Maxwellian tails and heating of core ions. In both cases, ion energization is accompanied by the formation of spatially narrow density dips. Inside these dips, double layers may easily be formed resulting in electron acceleration upwards or downwards depending on whether the electric field diverges or converges. The results are in qualitative agreement with relevant observations.
An unusual coronal mass ejection: First solar wind electron, proton, alpha monitor (SWEPAM) Results from the Advanced Composition Explorer
Authors: McComas D. J. , Bame S. J. , Barker P. L. , Delapp D. M. , Feldman W. C. , Gosling J. T. , Santiago E. , Skoug R. M. , Tokar R. L. , Riley P. , Phillips J. L. , Griffee J. W.
Published: February 2004

This paper reports the first scientific results from the Solar Wind Electron Proton Alpha Monitor (SWEPAM) instrument on board the Advanced Composition Explorer (ACE) spacecraft. We analyzed a coronal mass ejection (CME) observed in the solar wind using data from early February, 1998. This event displayed several of the common signatures of CMEs, such as counterstreaming halo electrons and depressed ion and electron temperatures, as well as some unusual features. During a portion of the CME traversal, SWEPAM measured a very large helium to proton abundance ratio. Other heavy ions, with a set of ionization states consistent with normal (1–2×106 K) coronal temperatures, were proportionately enhanced at this time. These observations suggest a source for at least some of the CME material, where heavy ions are initially concentrated relative to hydrogen and then accelerated up into the solar wind, independent of their mass and first ionization potential.
Nitrogen in solar energetic particles: Isotopically distinct from solar wind
Authors: Mathew K. J. , Kerridge J. F. , Marti K.
Published: February 2004

Stepwise etching of lunar soil ilmenite grains reveals that the 15N/14N ratio of implanted nitrogen decreases with increasing implantation depth within the ilmenite grains, i.e., with increasing energy of implantation. These results show that N derived from solar energetic particles, NSEP, is enriched in the light isotope, 14N, relative to solar‐wind nitrogen, NSW. This is in striking contrast to the neon isotopic record: NeSEP is depleted in the light isotope, 20Ne, relative to NeSW. These data suggest either distinct signatures in the respective solar source regions, or fractionation in the acceleration mechanism(s). However, the observed opposite fractionation trends for light N and Ne isotopes do not agree with model predictions.
Postseismic response of repeating aftershocks
Authors: Schaff David P. , Beroza Gregory C. , Shaw Bruce E.
Published: February 2004

The recurrence intervals of repeating earthquakes on the San Andreas Fault in the Loma Prieta aftershock zone follow the characteristic 1/t decay of Omori's law. A model in which these earthquakes occur on isolated patches of the fault that fail in stick‐slip with creep around them can explain this observation. In this model the recurrence interval is inversely proportional to the loading rate due to creep. Logarithmic velocity strengthening friction predicts 1/t decay in creep rate following the mainshock. The time dependence of recurrence is inconsistent with a simple viscous constitutive relationship, which predicts an exponential decay of loading rate. Thus, our observations imply postseismic slip at seismogenic depth under a power law rheology. The time dependence of postseismic deformation measured geodetically may be diagnostic of whether postseismic deformation is caused by creep or possible viscoelastic deformation at greater depths.
Second harmonic hectometric radio emission at Jupiter
Authors: Menietti J. D. , Gurnett D. A. , Groene J. B.
Published: February 2004

Galileo has been in orbit around Jupiter since December 1995. The plasma wave instrument on board the spacecraft has occasionally detected a rotationally modulated attenuation band in the hectometric (HOM) emission that most likely is due to scattering of the radiation from density fluctuations along the Io L‐shell, as reported earlier [cf. Gurnett et al., 1998]. The occurrence of the attenuation band is likely to be dependent on Io activity and the presence of density scattering centers along the Io L‐shell as well as the location of the source region. Some of the attenuation bands show clear indications of second harmonic emission. Without polarization measurements, it is difficult to place constraints on the local generation conditions based on the cyclotron maser instability, but the results imply that second harmonic emission could be present in the decametric (DAM) radiation as well. A survey of the data has revealed about 30 examples of second harmonic HOM.
Non‐equilibrium and unsteady fluid degassing during slow decompression
Authors: Hammer Julia E. , Manga Michael , Cashman Katharine V.
Published: February 2004

Decompression experiments were performed on corn syrup‐water solutions in order to investigate the effect of viscosity on processes of vesiculation and degassing at low to moderate degrees of volatile supersaturation. Repeat experiments demonstrated similar long term vesiculation behavior at moderate decompression rates despite highly variable initial nucleation styles. Results suggest that magmas may not necessarily achieve chemical equilibrium by vapor exsolution and may require viscosity‐dependent critical supersaturations in order to vesiculate. Vesiculation also increased the ambient pressure and decreased supersaturations, resulting in unsteady degassing.
Planetary‐wave modulation of PMSE
Authors: Kirkwood S. , Réchou A.
Published: February 2004

Variations in PMSE (Polar Mesosphere Summer Echo) occurrence with 4–6 day periods were observed by the ESRAD radar during the summer of 1997. These are compared with temperature fluctuations in 5‐day planetary waves extracted from the UKMO assimilated global data analyses. At the beginning and end of the PMSE season, the PMSE variations are closely anti correlated with temperature variations associated with 5‐day planetary waves at the 1 mb level. The planetary wave amplitudes expected at the mesopause are 1–2 K. This is found, by comparison with the seasonal decay of PMSE as the temperature rises at the end of the summer, to be sufficient to explain the observed 5–10% amplitude fluctuations in PMSE daily occurrence.
Discrete auroral arc, electrostatic shock and suprathermal electrons powered by dispersive, anomalously resistive field line resonance
Authors: Lotko W. , Streltsov A. V. , Carlson C. W.
Published: February 2004

Particle and field data from a 4100‐km‐altitude satellite pass through a 1.3‐mHz field line resonance, identified by ground‐based optical, magnetic and radar signatures, are compared with results from a two‐fluid MHD‐gyrokinetic simulation, including dispersively and resistively sustained parallel electric fields. It is shown that the resonance powers spatially adjacent up‐ and down‐going suprathermal‐electron fluxes, a 10‐km‐scale auroral arc and an imbedded electrostatic shock. Alfvén wave dispersion and anomalous plasma resistivity are key elements in the interpretation of the event.
Direction‐finding measurements of heliospheric 2–3 kHz radio emissions
Authors: Gurnett D. A. , Allendorf S. C. , Kurth W. S.
Published: February 2004

Using data from the Voyager 1 plasma wave instrument, a series of direction‐finding measurements is presented for the intense 1992–93 heliospheric 2‐ to 3‐kHz radio emission event, and several weaker events extending into 1994. Direction‐finding measurements can only be obtained during roll maneuvers, which are performed about once every three months. Two parameters can be determined from the roll‐induced intensity modulation, the azimuthal direction of arrival (measured around the roll axis), and the modulation index (the peak‐to‐peak amplitude divided by the peak amplitude). Measurements were made at two frequencies, 1.78 and 3.11 kHz. No roll modulation was observed at 1.78 kHz, which is consistent with an isotropic source at this frequency. In most cases an easily measurable roll modulation was detectable at 3.11 kHz. Although the azimuth angles have considerable scatter, the directions of arrival at 3.11 kHz can be organized into three groups, each of which appears to be associated with a separate upward drifting feature in the radio emission spectrum. The first group, which is associated with the main 1992–93 event, is consistent with a source located near the nose of the heliosphere. The remaining two groups, which occur after the main 1992–93 event, have azimuth angles well away from the nose of the heliosphere. The modulation indexes vary over a large range, from 0.06 to 0.61, with no obvious trend. Although the variations in the directions of arrival and modulation indicies appear to reflect changes in the position and angular size of the source, it is also possible that they could be caused by refraction or scattering due to density structures in the solar wind.
IUE views Europa: Temporal variations in the UV
Authors: Domingue Deborah L. , Lane Arthur L.
Published: February 2004

Observations taken with the International Ultraviolet Explorer (IUE) show the first detection of temporal changes in the UV spectral reflectance of the Jovian quadrant of Europa's leading side between 15°–75° longitude over a time scale considered extraordinarily short for a large planetary object (commensurate with possible resurfacing events). The central trailing side region displays a 0.28 µm SO2 absorption that has remained constant in relative depth over the past decade to within the instrument detection limits. A new 0.33 µm absorption feature is seen on the leading side.
Multi‐fluid simulations of the magnetosphere: The identification of the geopause and its variation with IMF
Authors: Winglee R. M.
Published: February 2004

A new multi‐fluid global treatment is presented that separately tracks the solar wind and ionospheric plasmas in the magnetosphere. The model is used to identify the density and pressure geopauses, i.e. the boundaries where the contributions to the magnetospheric density or pressure from the ionosphere equals that from the solar wind. The density geopause is primarily restricted to the inner magnetosphere and central lobes for northward interplanetary magnetic field (IMF) but during southward IMF it can extend into middle magnetosphere due to enhanced ionospheric outflow and convection. This variation is consistent with recent statistical studies that show that the plasma sheet density is correlated with the solar wind density, particularly during northward IMF.
Absence of multiple steady states and a transition from steady state to monotonic growth behavior of [CO] and [O3] in a simple, nonlinear, oscillatory model of tropospheric photochemistry
Authors: Kalachev Leonid V. , Field Richard J.
Published: February 2004

The existence of multiple steady states is investigated in a simple photochemical reaction mechanism with the following properties: (1) it is derived from tropospheric chemistry, (2) it is governed by a nonlinear dynamic law, and (3) it exhibits temporal oscillations in the concentrations of its component chemical species. It is shown that chemical steady states for this mechanism can be located analytically using methods often also applicable to similar mechanisms. It is found that multiple steady states do not exist in this particular mechanism. Such an analytical treatment displays the dynamic structure of the mechanism, avoids numerical searching for steady states, and allows here for the identification and location of a transition (bifurcation) from steady‐state to monotonic‐growth behavior of [CO] and [O3] as the influx of NO increases at fixed values of the influxes of O3 and CO. Thus an atmosphere is seen to lose its ability to photochemically cleanse itself of CO at sufficiently high influx of NO. It is suggested that multiple steady states may be introduced into this mechanism by addition of transport or a well‐known, hydrocarbon‐based, radical‐multiplication reaction.
Flow of bottom and deep water in the Amirante Passage and Mascarene Basin
Authors: Johnson Gregory C. , Musgrave David L. , Warren Bruce A. , Ffield Amy , Olson Donald B.
Published: February 2004

In the Indian Ocean the Amirante Passage is the sill through which relatively cold, fresh, oxygen‐rich, and nutrient‐poor bottom water spreads northward into the Somali Basin from the Mascarene Basin. The passage is also a conduit through which relatively warm, salty, oxygen‐poor, and nutrient‐rich deep water spreads south. Previous estimates for northward transport of bottom water in the passage have been made from station pairs and sections without benefit of tracer measurements. Previous estimates of southward transport of deep water are scarce. Three hydrographic sections were made across the passage in 1995 and 1996 as part of the World Ocean Circulation Experiment (WOCE). Two WOCE sections were also made perpendicular to the western boundary in the Mascarene Basin, just south of the passage. The geostrophic shear field is used with the salinity, dissolved oxygen, and silica distributions to select a range of zero‐velocity surfaces (ZVSs) on potential isotherms from 1.0° to 1.1°C (hence a range of geostrophic transports) for which the flow direction is consistent with the tracer distributions. Objective mapping is used to obtain flux estimates below the deepest common level of station pairs. Estimates in the Mascarene Basin result in a bottom water volume transport from 2.5 to 3.8 × 106 m3 s−1 northward toward the passage below the ZVSs and a deep‐water transport between the ZVSs and 2.5°C from 11.6 to 6.4 × 106 m3 s−1 southward. Estimates within the passage result in transports from 1.0 to 1.7 × 106 m3 s−1 northward for the bottom water and from 8.6 to 3.8 × 106 m3 s−1 southward for the deep water.
Evidence of transport in water vapor profiles at mid latitudes from Stratospheric Aerosol and Gas Experiment(SAGE II) measurements
Authors: Kar J. , Mahajan K. K.
Published: February 2004

In this paper we examine water vapor measurements from the Stratospheric Aerosol and Gas Experiment II and present some midlatitude water vapor profiles which appear different from the normal profiles at these latitudes. They have maxima and minima as seen in the tropical profiles by Mote et al. [1996] from the Upper Atmosphere Research Satellite measurements. The occurrence statistics of these profiles are studied for the year 1988. These characteristic profiles at extratropical latitudes may indicate filaments of air that might have been advected episodically from the tropics (or sometimes from the polar regions) and, as such, may be used as signatures of transported air at such latitudes. The fractional abundance of these profiles has been used to get a qualitative measure of the transport.
Air chemistry during the 1995 SOS/Nashville intensive determined from level 2 network
Authors: Olszyna Kenneth J. , Parkhurst William J. , Meagher James F.
Published: February 2004

Air quality measurements from enhanced ground‐based air monitoring stations, that were located at strategic urban, suburban, and rural (regional) locations, were used to determine the factors controlling excess ozone formation in the Nashville area. During the 6 week intensive study period, the daily maximum hourly O3 concentrations varied from daytime highs of less than 40 ppbv to values exceeding 120 ppbv. The higher O3 concentrations were observed at the urban and suburban locations, and the highest O3 value of 138 ppbv was observed at the downtown Nashville station. On 12 days, one or more of the urban and suburban stations exceeded midday 8‐hour mean O3 concentrations of 80 ppbv in contrast to the single occurrence at the rural stations. The observations that the elevated O3 concentrations occurred more frequently at the urban and suburban stations during stagnating weather conditions suggest localized production of excess O3. The comparison of the O3/NOy ratios to model simulations suggest that the rural and suburban locations are in a NOx sensitive chemistry regime, while the urban location (downtown Nashville) is in a chemistry regime that is sensitive to both NOx and VOC concentrations. The O3 production efficiency, determined from the slope of the O3 versus NOz (NOy ‐ NOx), was found to be similar between the Dickson and Youth suburban stations and the Giles rural/regional station. The segregation of the data by SO2 concentration showed lower O3 production efficiency for those measurement periods with SO2 concentrations greater than 2 ppbv. The slopes (upper limits of O3 production efficiency) ranged from 7.7 to 10.6 for the lower SO2 concentrations and from 4.4 to 4.6 for the higher SO2 concentrations.
Comparison of atmospheric clear‐sky shortwave radiation models to collocated satellite and surface measurements in Canada
Authors: Jing Xiaodu , Cess Robert D.
Published: February 2004

To address a recent issue of whether contemporary clear‐sky shortwave radiative transfer models do or do not portray reality, we have collocated satellite measurements of reflected shortwave radiation at the top of the atmosphere, made as part of the Earth Radiation Budget Experiment, with measurements of surface insolation made at 24 stations located throughout southern Canada. From this, a clear‐sky data set has been constructed by using both the satellite and the surface measurements to identify clear days, and the data set extends over a 4‐year period (1985–1988). Two quite different types of shortwave radiative transfer models were employed, one a model‐derived algorithm that converts the top‐of the‐atmosphere measurements to surface insolation, and the other a stand‐alone column model which computes the surface insolation independently of the satellite measurements. Both models incorporate prescribed aerosols, and they were compared to the clear‐sky data by using satellite‐measured atmospheric water vapor as model input. The models are in excellent agreement with the clear‐sky measurements when averaging is performed over all stations and over all seasons. The relative bias error in surface insolation is roughly 1% for both models, despite the fact that one model is constrained to the top‐of‐the‐atmosphere measurements and the other is not. Thus the models' incorporation of tropospheric aerosols seems quite realistic when compared to the averaged data. For daily means and individual stations, however, the models' relative bias errors in surface insolation are observed to range from −6% to 10%, and it is demonstrated that this is caused by temporal and geographic variability in tropospheric aerosol loading. Because the models incorporate prescribed aerosols, they produce a relative bias error of roughly −6% for aerosol‐free conditions. The opposite limit of 10% corresponds to aerosol loading in excess of that prescribed in the models. There is no evidence that the models incorrectly portray any important physical processes, and we find no support for a suggestion that there is an unknown and substantial source of shortwave absorption by water vapor. Our comparisons do not, however, rule out recently suggested minor absorbers of shortwave radiation. Also, since a very stringent clear‐sky identification procedure was used with the goal of removing forest fire smoke as well as clouds, our study does not rule out possible atmospheric absorbers resulting from urban pollution.