bluuebunny/crossref_metadata_2025 huggingface dataset:
Shapes, sizes and light scattering properties of ice crystals in cirrus and a persistent contrail during SUCCESS
Authors: Lawson R. Paul , Heymsfield Andrew J. , Aulenbach Steven M. , Jensen Tara L.
Published: February 2004

A persistent contrail in the shape of a racetrack was generated by the NASA DC‐8 research aircraft during the SUCCESS project. The contrail was visible on GOES imagery for six hours. Microphysical measurements collected by the DC‐8 show that after 40 min the core of the contrail contained mostly small (1 to 20 µm) ice particles in concentrations >1000 L−1, with larger (>300 µm) ice crystals in concentrations <10−6L−1. In contrast to the core, the contrail periphery contained about an order of magnitude less ice particles in the 1 → 20 µm range and about three orders of magnitude more ice particles >300 µm. The larger ice crystals in the periphery were mostly columns and bullet rosettes, similar to habits of larger ice crystals found in ambient cirrus in the area. Measurements suggest that the shape of phase functions of randomly‐oriented columns and rosettes are mostly featureless. The measured phase functions are closest in shape to those predicted by ray‐tracing theory for random‐fractal and spatial‐dendrite ice crystals.
Entry of the POLAR spacecraft into the polar cusp under northward IMF conditions
Authors: Russell C. T. , Fedder J. A. , Slinker S. P. , Zhou X.‐W. , Le G. , Luhmann J. G. , Fenrich F. R. , Chandler M. O. , Moore T. E. , Fuselier S. A.
Published: February 2004

On May 29, 1996 from 0200 to 0800 UT the solar wind dynamic pressure was high ranging from 6 to 8 nPa and the interplanetary field was almost due northward, ranging from 10 to 15 nT in BZ GSM. Even at apogee the POLAR spacecraft should not have entered the magnetosheath according to recent scaling laws. However, the magnetic field was greatly depressed below the value expected indicating the presence of significant plasma energy density throughout the high latitude magnetosphere surrounding the cusp. The presence of this plasma is confirmed by the plasma instrumentation on board the spacecraft. While the entry into this nearly stagnant plasma was gradual, the exit on to polar cap field lines was abrupt. We interpret these observations in terms of the post‐cusp reconnection of the strongly northward interplanetary magnetic field.
Diffusion of HNO3 in ice
Authors: Sommerfeld Richard A. , Knight Charles A. , Laird S. Kay
Published: February 2004

We designed a series of experiments to verify the value of the diffusion coefficient of HNO3 in ice at −15° C using a serial sectioning technique. Our first series of experiments with diffusion times of 70 to 100 h gave an average value of about 1.7 × 10−11 cm² s−1 (StD 0.8 × 10−11) and a second set of experiments at 1000 h resulted in an apparent diffusion coefficient of 10−12 cm² s−1. Our conclusion is that the observed gradients of HNO3 in ice were spurious and the result of serial contamination of the surfaces during sectioning of the ice. We call the diffusion coefficients “apparent” because in the present experiment we could not distinguish between an undetectable diffusion coefficient and undetectable solubility. In either case, the validity of the previously published results is questionable.
The elemental composition of low altitude 0.49 MeV/nucleon trapped equatorial ions
Authors: Mazur J. E. , Mason G. M. , Greenspan M. E.
Published: February 2004

Using instrumentation on board the SAMPEX satellite at ∼600 km we present new measurements of the composition of a population of >0.49 MeV/nucleon ions that are trapped near the geomagnetic equator. These ions gain access to the SAMPEX orbit as neutral particles via charge exchange collisions that continually occur within the higher altitude radiation belt and contribute to the decay of storm‐time enhanced ring current. At low altitudes a second charge exchange collision produces a trapped ion belt near the magnetic equator. This belt is ephemeral, as it is necessarily observed on drift paths that reach deep into the atmosphere near the South Atlantic Anomaly. We find the relative abundances of H:He:C:O:Ne‐Fe are 7000 : 7.5 : 0.14 : 1.0 : 0.03. The low altitude particles are underabundant in Z>8 ions compared to the radiation belt, possibly because the radiation belt Z>8 ions may not be stably trapped once they charge exchange to higher rigidities. We cannot rule out the possible contribution of trapped anomalous cosmic rays to the heavy ions observed above 0.49 MeV/nucleon in this low altitude population.
Solar variability and climate change: Geomagnetic aa index and global surface temperature
Authors: Cliver E. W. , Boriakoff V. , Feynman J.
Published: February 2004

During the past ∼120 years, Earth's surface temperature is correlated with both decadal averages and solar cycle minimum values of the geomagnetic aa index. The correlation with aa minimum values suggests the existence of a long‐term (low‐frequency) component of solar irradiance that underlies the 11‐year cyclic component. Extrapolating the aa‐temperature correlations to Maunder Minimum geomagnetic conditions implies that solar forcing can account for ∼50% or more of the estimated ∼0.7–1.5°C increase in global surface temperature since the second half of the 17th century. Our analysis is admittedly crude and ignores known contributors to climate change such as warming by anthropogenic greenhouse‐gases or cooling by volcanic aerosols. Nevertheless, the general similarity in the time‐variation of Earth's surface temperature and the low‐frequency or secular component of the aa index over the last ∼120 years supports other studies that indicate a more significant role for solar variability in climate change on decadal and century time‐scales than has previously been supposed. The most recent aa data for the current solar minimum suggest that the long‐term component of solar forcing will level off or decline during the coming solar cycle.
First direct sulfuric acid detection in the exhaust plume of a jet aircraft in flight
Authors: Curtius J. , Sierau B. , Arnold F. , Baumann R. , Busen R. , Schulte P. , Schumann U.
Published: February 2004

Sulfuric acid (SA) was for the first time directly detected in the exhaust plume of a jet aircraft in flight. The measurements were made by a novel aircraft‐based VACA (Volatile Aerosol Component Analyzer) instrument of MPI‐K Heidelberg while the research aircraft Falcon was chasing another research aircraft ATTAS. The VACA measures the total SA in the gas and in volatile submicron aerosol particles. During the chase the engines of the ATTAS alternatively burned sulfur‐poor and sulfur‐rich fuel. In the sulfur‐rich plume very marked enhancements of total SA were observed of up to 1300 pptv which were closely correlated with ΔCO2 and ΔT and were far above the local ambient atmospheric background‐level of typically 15–50 pptv. Our observations indicate a lower limit for the efficiency ε for fuel‐sulfur conversion to SA of 0.34 %.
NASA scatterometer provides global ocean‐surface wind fields with more structures than numerical weather prediction
Authors: Liu W. Timothy , Tang Wenqing , Polito Paulo S.
Published: February 2004

The major differences between monthly‐mean ocean‐surface wind fields derived from the observations of the National Aeronautics and Space Administration (NASA) Scatterometer (NSCAT) and produced by the operational numerical weather prediction (NWP) model of the European Center for Medium‐Range Weather Forecasts are found in coastal and equatorial regions, where the sharp changes are smoothed over in NWP products; these wind differences are explained to be the result of the superior spatial resolution of NSCAT winds. Objective interpolation of NSCAT data alleviates errors caused by the uneven satellite sampling and retains greater energy content of NSCAT winds at high wavenumbers.
FAST satellite observations of large‐amplitude solitary structures
Authors: Ergun R. E. , Carlson C. W. , McFadden J. P. , Mozer F. S. , Delory G. T. , Peria W. , Chaston C. C. , Temerin M. , Roth I. , Muschietti L. , Elphic R. , Strangeway R. , Pfaff R. , Cattell C. A. , Klumpar D. , Shelley E. , Peterson W. , Moebius E. , Kistler L.
Published: February 2004

We report observations of “fast solitary waves” that are ubiquitous in downward current regions of the mid‐altitude auroral zone. The single‐period structures have large amplitudes (up to 2.5 V/m), travel much faster than the ion acoustic speed, carry substantial potentials (up to ∼100 Volts), and are associated with strong modulations of energetic electron fluxes. The amplitude and speed of the structures distinguishes them from ion‐acoustic solitary waves or weak double layers. The electromagnetic signature appears to be that of an positive charge (electron hole) traveling anti‐earthward. We present evidence that the structures are in or near regions of magnetic‐field‐aligned electric fields and propose that these nonlinear structures play a key role in supporting parallel electric fields in the downward current region of the auroral zone.
MSX satellite observations of thunderstorm‐generated gravity waves in mid‐wave infrared images of the upper stratosphere
Authors: Dewan E. M. , Picard R. H. , O'Neil R. R. , Gardiner H. A. , Gibson J. , Mill J. D. , Richards E. , Kendra M. , Gallery W. O.
Published: February 2004

Data from the Midcourse Space Experiment (MSX) has provided the first observations of thunderstorm‐generated gravity waves imaged from space. Gravity wave theory predicts that isolated, sufficiently convective thunderstorms can launch waves and create a unique intensity pattern of concentric circles on a radiating surface of constant altitude above such a storm. Among the MSX constant‐nadir‐angle mid‐wave infrared (MWIR) observations, two instances of such patterns have been identified. It was confirmed from meteorological satellite images that highly convective isolated thunderstorms occurred at the locations and times expected.
Airborne observations of aircraft aerosol emissions II: Factors controlling volatile particle production
Authors: Anderson B. E. , Cofer W. R. , Barrick J. D. , Bagwell D. R. , Hudgins C. H.
Published: February 2004

Airborne measurements of fine and ultrafine aircraft aerosol emissions are examined as a function of environmental conditions, fuel sulfur content, and aircraft type, to determine what factors influence the abundance of volatile particles and what the likely composition of these particles are. The data were obtained from aboard a small jet aircraft flying in near‐field (<20 km aircraft separation) wakes generated by a variety of aircraft. All aircraft produced large numbers of particles relative to background concentrations, a majority of which evaporated at temperatures <200°C. The volatile particles, except under humid conditions, were typically <20 nm in diameter, and their numbers varied both as a function of atmospheric conditions and plume age. Their apparent number‐density dependence upon fuel sulfur content, and the fact that their inferred mass concentrations are less than the reported shortfall in gas phase sulfur budgets, strongly suggests they were primarily composed of condensed sulfur species.
Simulation of the March 9, 1995, substorm: Auroral brightening and the onset of lobe reconnection
Authors: Lyon J. G. , Lopez R. E. , Goodrich C. C. , Wiltberger M. , Papadopoulos K.
Published: February 2004

A global MHD simulation of an isolated substorm that occurred on March 9, 1995 is presented. The simulation, driven with solar wind data provided by the Wind satellite, reproduced to a surprising degree the evolution of substorm activity. The onset of the expansion phase was coincident with the penetration of an electric field spike into the near‐Earth region. This impulse launched a tailward propagating signal (rarefaction wave) that enhanced reconnection in the mid tail. Substorm intensification was correlated with the enhancement of the reconnection rate at the preexisting reconnection region located at 30 RE. The importance of the electric field spike in correlating ionospheric and magnetospheric aspects of the substorm is emphasized.
Structures in sporadic‐E observed with an impedance probe during the SEEK Campaign: Comparisons with neutral‐wind and radar‐echo observations
Authors: Yamamoto Masayuki , Ono Takayuki , Oya Hiroshi , Tsunoda Roland T. , Larsen Miguel F. , Fukao Shoichiro , Yamamoto Mamoru
Published: February 2004

In order to clarify the origin of the so‐called quasi periodic echoes (QPE) that have been often detected by radar observations in the presence of sporadic‐E (Es) layers in the nighttime midlatitude ionosphere, two sounding rockets were launched during the SEEK (Sporadic‐E Experiment over Kyushu) campaign. Each rocket carried a swept‐frequency impedance probe to measure the E‐region electron‐density (Ne) profile. Using the four Ne profiles obtained during the two rocket flights together with a neutral‐wind profile obtained from a trimethyl aluminum (TMA) chemical release experiment on one of the rockets and QPE obtained with a ground‐based radar, we consider the role of wind shear in the formation of the observed Es layers, and the question of whether QPE are associated with Es layers that are modulated in altitude. The Ne profiles of Es structures that were obtained in the presence of QPE were characterized by the highly concentrated thin layers. The formation of such a thin layer by a neutral‐wind shear process was confirmed in comparison with the TMA measurements. The peak Ne values of the Es layers ranged from 2.2 to 9.3 × 104 el/cm³ near 100‐km altitude. These primary Es layers were accompanied by significant secondary structures that were located about 12 to 20 km above the main Es layers and had peak Ne that ranged from 5.2 × 10³ to 1.3×104 el/cm³. The average altitude profiles of QPE approximately covered the range where the Es‐layer peaks appeared. Our principal finding is that the observed Es structures tended to resemble horizontally stratified layers rather than structures with deep altitude modulation like previous QPE model, although the rocket measurements were separated from those by radar by 90 to 145 km.
Warming and freshwater budget change in the Mediterranean since the 1940s, their possible relation to the greenhouse effect
Authors: Béthoux Jean‐Pierre , Gentili Bernard , Tailliez Dominique
Published: February 2004

Temperature and salinity of Mediterranean deep water have been increasing, based on observations extending back to 1959. Over the 1940–1995 period, the corresponding changes in heat and water budgets across the sea surface have been estimated to be 1.74 Wm−2 for the greenhouse effect change, 0.5°C and 0.4°C for mean air and sea‐surface temperature increases, respectively, and an increase of 0.1 m (or 11%) in the freshwater deficit, which is due partly to human activities and partly to climatic changes.
Radar probing of cirrus and contrails: Insights from 2D model simulations
Authors: Sassen Kenneth , Khvorostyanov Vitaly I.
Published: February 2004

Millimeter wavelength radars promise certain advantages over lidar techniques for the study of ice clouds, including quantitative data retrieval and the ability to penetrate multiple level clouds. However, the problems in deriving ice cloud content are formidable. In this study the microphysical output of a 2D model with explicit microphysics is converted to radar reflectivity to explore the underlying physics, and problems related to radar ice cloud probing. It is concluded that simple relations based on radar reflectivity will likely yield ambiguous estimates of ice mass content because of characteristic vertical variations in cloud content that evolve with cirrus growth. The weak signals (<∼−40 dBZ1) produced by the micron‐sized particles present in cirrus cloud‐top generating layers, and in persisting contrails, make their detection by most radars problematic.
Broadband water vapor absorption of solar radiation tested using ARM data
Authors: Fu Qiang , Lesins G. , Higgins J. , Charlock T. , Chylek P. , Michalsky J.
Published: February 2004

A high quality data set collected at the ARM SGP central facility is analyzed to identify the water vapor‐related anomalous absorption of solar radiation. We focus on the direct solar broadband surface irradiances under cloud‐free conditions in the April 1994 CAGEX and summer 1996 periods. A radiation model without including the H2O continuum in the solar spectrum is compared with observations. This comparison reveals a mean bias of 4.5 W m−2 that is roughly equivalent to a globally averaged bias of ∼2 W m−2. It is therefore unlikely that the excess absorption suggested by recent studies can be attributed to the H2O continuum. We also show that the difference between calculated and observed irradiances has a very weak correlation with water vapor. It is suggested that the discrepancy between model and observations is largely due to the uncertainties associated with aerosol optical properties.
The hydrothermal system at Soufriere Hills Volcano, Montserrat (West Indies): Characterization and role in the on‐going eruption
Authors: Boudon Georges , Villemant Benoît , Komorowski Jean‐Christophe , Ildefonse Philippe , Semet Michel P.
Published: February 2004

Mineralogical, microtextural and geochemical studies have been performed on altered volcanic products from active hydrothermal areas, on phreatic tephra from the 1995 activity and on fragments from older Castle Peak dome and the present (1995–97) dome. The mineral assemblages of the hydrothermal system (primarily silica‐polymorphs) are typical of the upper alteration zone of a high sulfidation system. Volatile and mobile elements chemistry show no evidence of interaction between the hydrothermal system and erupting magmas. These results suggest that the on‐going eruption conduits are isolated from the hydrothermal system due to precipitation of vapor transported silica which drastically reduces the magma degassing through country rocks.
Generalized ion ring instability driven by ions with a partial shell distribution
Authors: Cao J. B. , Zhou G. C. , Wang X. Y.
Published: February 2004

A generalized ion ring instability driven by energetic ions with a shell velocity distribution, which has a central pitch angle at 90°, is studied. We consider waves propagating in both parallel and oblique direction as well as different pitch angle spreads of a partial shell. These unperturbed distributions represent different stages during the time evolution of an ion distribution, that is a ring initially. The evolution is attributed to pitch angle scattering due to wave‐particle interactions. Numerical results obtained by us show that the instability diminishes rapidly, especially for oblique propagation, while the pitch angle spread increase.
Inelastic yielding and forebulge shape across a modern foreland basin: North West Shelf of Australia, Timor Sea
Authors: Lorenzo Juan M. , O'Brien Geoffrey W. , Stewart Jonathan , Tandon Kush
Published: February 2004

The Timor Trough is a modern ‘underfilled’ foreland basin created by partial subduction of the outer north west continental shelf of Australia beneath Timor Island in the Outer Banda Arc of eastern Indonesia during the Cenozoic. A change of the effective elastic thickness (EET) of the continental foreland lithosphere from ∼80±20 km to ∼25 km over a distance of ∼300 km explains (1) the high curvature (∼10−7 m−1) on the outer Trough wall, (2) the low shelf forebulge (∼200 m) as measured along a reference base Pliocene unconformity, and (3) observed gravity. An inelastically yielding quartzite‐quartz‐diorite‐dunite continental rheology can explain the EET gradient. New, shallow crustal (<8 km), seismic reflection images indicate that Jurassic basement normal faults are reactivated during bending of the foreland.
Aircraft observations conjugate to FAST: Auroral arc thicknesses
Authors: Stenbaek‐Nielsen H. C. , Hallinan T. J. , Osborne D. L. , Kimball J. , Chaston C. , McFadden J. , Delory G. , Temerin M. , Carlson C. W.
Published: February 2004

Optical observations conjugate to the FAST satellite show good agreement between the widths of auroral structures observed optically and those inferred from the measured electron energy flux. The implication is that these structures are imposed by processes at or above the ∼4000 km altitude of FAST. A variety of widths down to about 2 km were observed, but there were no examples of finer scale structures. A pre‐breakup weak discrete arc at the poleward edge of the diffuse aurora showed electron produced optical structures located on either side of upward going ion beams. The optical emission in the equator‐ward part of the diffuse aurora was caused almost exclusively by precipitating ions. The optical observations were made over northern Alaska between Jan 31 and Feb 16, 1997, from a jet aircraft carrying an all‐sky and three narrow‐field TV cameras.
Generation of mega‐plumes from the core‐mantle boundary in a compressible mantle with temperature‐dependent viscosity
Authors: Thompson Paul F. , Tackley Paul J.
Published: February 2004

We have investigated the development of axisymmetric mantle plumes in a compressible mantle with temperature‐dependent viscosity, using two different values for the thermal activation energy. Thermodynamic parameters were based on realistic Earth values in the shallow mantle. We assumed a compressible mantle with a phase transition and a two layer viscosity structure (mantle 30 times more viscous beneath the phase change). A dramatic transition in plume dynamics occurred as the thermal activation energy was increased from 250 to 500 kJ mol−1. A “mega‐plume” was formed from the merging of small‐scale instabilities swept into the plume's axis, rapidly flushing the entire contents of the hot thermal boundary layer into the upper mantle. Hot plume material with a temperature anomaly of 250 K reached the lithosphere for our assumed temperature drop of 500 K across the base of the mantle. Viscous heating over four orders of magnitude greater than chondritic radiogenic sources was observed during the initial plume‐lithosphere interaction.
Three‐dimensional P‐wave velocity structure of Mt. Etna, Italy
Authors: Villaseñor A. , Benz H. M. , Filippi L. , De Luca G. , Scarpa R. , Patanè G. , Vinciguerra S.
Published: February 2004

The three‐dimensional P‐wave velocity structure of Mt. Etna is determined to depths of 15 km by tomographic inversion of first arrival times from local earthquakes recorded by a network of 29 permanent and temporary seismographs. Results show a near‐vertical low‐velocity zone that extends from beneath the central craters to a depth of 10 km. This low‐velocity region is coincident with a band of steeply‐dipping seismicity, suggesting a magmatic conduit that feeds the summit eruptions. The most prominent structure is an approximately 8‐km‐diameter high‐velocity body located between 2 and 12 km depth below the southeast flank of the volcano. This high‐velocity body is interpreted as a remnant mafic intrusion that is an important structural feature influencing both volcanism and east flank slope stability and faulting.
Could Mars be dark and altered?
Authors: Calvin Wendy M.
Published: February 2004

There is a long known dichotomy in the martian albedo, with an associated, but mostly assumed, mineralogical split as well. The bright red regions are inferred to be weathered, oxidized dust and the dark grey regions unaltered volcanic material. A number of recent analyses suggest this division is unnaturally simplistic and the association of many dark regions with the former presence of water requires a re‐examination of the spectra in light of potential alteration minerals. I present an alternate interpretation of the reflectance spectral characteristics of some dark regions on Mars that includes dark layer silicates. If their presence is confirmed on Mars this will have implications for sequestration of current and past volatile inventories, clues to the extent and type of geochemical weathering, and potential zones where bacterial life forms may have emerged.
Three‐year decline of magmatic CO2emissions from soils of a Mammoth Mountain Tree Kill: Horseshoe Lake, CA, 1995–1997
Authors: Gerlach Terrence M. , Doukas Michael P. , McGee Kenneth A. , Kessler Richard
Published: February 2004

We used the closed chamber method to measure soil CO2efflux over a three‐year period at the Horseshoe Lake tree kill (HLTK)—the largest tree kill on Mammoth Mountain in central eastern California. Efflux contour maps show a significant decline in the areas and rates of CO2emission from 1995 to 1997. The emission rate fell from 350 t d−1(metric tons per day) in 1995 to 130 t d−1in 1997. The trend suggests a return to background soil CO2efflux levels by early to mid 1999 and may reflect exhaustion of CO2in a deep reservoir of accumulated gas and/or mechanical closure or sealing of fault conduits transmitting gas to the surface. However, emissions rose to 220 t d−1on 23 September 1997 at the onset of a degassing event that lasted until 5 December 1997. Recent reservoir recharge and/or extension‐enhanced gas flow may have caused the degassing event.
Linear partitioning theory applied to the Earth's 410‐km discontinuity
Authors: Morse S. A.
Published: February 2004

The theory of linear partitioning in binary solutions is here extended to solid‐solid equilibria in P‐X space at constant T, with general rules for formulating the linear relationship. When the interphase partition coefficient, formulated for the Fe endmember, is linear with the composition of the numerator phase, the exchange coefficient KD is constant, and vice versa. For olivine ‐ wadsleyite in P‐X, the four best experimental brackets in the literature give KD = 0.56 ± 0.02 (1‐s.d.) at 1600°C. The S‐S transition at XFe = 0.1 is 2.8 kb or about 8 km wide for pure olivine. Half the olivine is converted to wadsleyite at 0.6 the P interval. However, a transition zone lid ≤4 km thick is consistent with a multiphase mantle in which the presence of a non‐transforming phase (e.g., pyroxene) cuts the effective transformation window in half as recently shown by L. Stixrude.
Primordial helium and neon in the Earth—A speculation on early degassing
Authors: Honda Masahiko , McDougall Ian
Published: February 2004

Primordial helium‐neon abundance ratios in the Earth have been accurately determined, based on helium and neon isotopic systematics observed in mid‐ocean ridge basalts (MORBs) and Hawaiian ocean island basalt (OIB) samples. The mean primordial ³He/22Ne ratios for the MORB and Hawaiian OIB samples are 10.2±1.6 and 6.0±1.4, respectively. The gross average of all values is 7.7±2.6, about twice the solar ³He/22Ne ratio of 3.8. Thus, primordial helium and neon in the Earth are elementally fractionated from the solar composition, noting, however, that the Earth's primordial helium and neon are isotopically solar in composition. This elemental fractionation between helium and neon was probably caused by solubility‐controlled degassing processes at an early stage of the Earth's evolution.
An unusual rotationally modulated attenuation band in the Jovian hectometric radio emission spectrum
Authors: Gurnett D. A. , Kurth W. S. , Menietti J. D. , Persoon A. M.
Published: February 2004

A well‐defined attenuation band modulated by the rotation of Jupiter has been found in the spectrum of Jovian hectometric radiation using data from the Galileo plasma wave instrument. The center frequency of this band usually occurs in the frequency range from about 1 to 3 MHz and the bandwidth is about 10 to 20 percent. The center frequency varies systematically with the rotation of Jupiter and has two peaks per rotation, the first at a system III longitude of about 50°, and the second at about 185°. It is now believed that the attenuation occurs as the ray path from a high‐latitude cyclotron maser source passes approximately parallel to the magnetic field near the northern or southern edges of the Io L‐shell. The peak at 50° system III longitude is attributed to radiation from a southern hemisphere source and the peak at 185° is from a northern hemisphere source. The attenuation is thought to be caused by coherent scattering or shallow‐angle reflection from field‐aligned density irregularities near the Io L‐shell. The narrow bandwidth indicates that the density irregularities are confined to a very narrow range of L values (Δ L = 0.2 to 0.4) near the Io L‐shell.
Porosity of very young oceanic crust from sea floor gravity measurements
Authors: Pruis Matthew J. , Johnson H. Paul
Published: February 2004

Porosity and density are two of the most important, but under‐determined parameters in studies of igneous oceanic crust. Lacking quantitative measurements of crustal densities, but with plausible expectations of substantial variation with age, previous investigators have used estimates that have varied widely. To address this problem more rigorously, a recent ALVIN program obtained 133 on‐bottom gravity stations to calculate crustal densities for three recent volcanic eruptions on the Juan de Fuca Ridge. In the summer of 1995, a Bell‐Aerospace BGM‐3 gravity meter was mounted in ALVIN and made fixed‐station gravity measurements on 11 transect lines from three distinct volcanic environments including (1) the recent CoAxial Segment volcanic eruption that occurred in 1993, (2) two nearby flows with less well‐determined ages but dated post‐1981, and (3) several older adjacent areas on the Juan de Fuca axial ridge. Densities for the recent eruptive units ranged between 2280 and 2450 kg/m³, while the upper 50 meters of the older, unfractured surrounding flows were approximately 2800 kg/m³. Laboratory grain densities measured from rocks collected in the study area allow crustal porosities to be calculated, which are anomalously high for the recent flows in comparison to the surrounding axial ridge. Porosities for the three youngest flows range between 29–36%, while the adjacent unfractured regions of the surrounding axial region had porosities near 10%. Two localized regions of intense surficial crustal fracturing in older crust, located just south of the 1993 eruption site, also had high porosities of 26–28%. This high variability indicates that the evolution of crustal porosities from young to older oceanic crust is not related only to the collapse and infilling of macroscopic voids, but that tectonic activity can significantly modify the porosity of older crustal structures.
On the reconstruction of the transfer function for atmospherically generated seiches
Authors: Monserrat S. , Rabinovich A. B. , Casas B.
Published: February 2004

A method recently proposed to separate source and topographic effects in observed tsunami spectra is revised and applied to atmospherically generated seiches. The method is used to investigate the origin of abnormal seiche events (‘rissaga waves’) recorded in the region of Ciutadella, Balearic Islands. The reconstructed open‐sea source spectra and the observed atmospheric pressure spectra are combined to estimate the ‘transfer function’ between the atmosphere and the sea surface. This function is used to predict sea level spectra for given locations near to the coast. Theoretically computed spectra for two ‘rissaga’ events are in good agreement with observations.
Pollen evidence for increased summer rainfall in the medieval warm period at Maili, northeast China
Authors: Ren Guoyu
Published: February 2004

A 2000‐year fossil pollen series from Maili Bog, Northeast China, is presented. In the pollen record, which has a time resolution of 28 years during the last 1000 years, the period 1000–660 yr. BP stands out as unique because it witnessed a remarkably increased pollen accumulation for almost all the taxa. This change could not be explained by the relaxation of human interference stress, because population density and intensity of agricultural activities during Liao and Jin Dynasties (AD 916 to AD 1234) were generally larger than any previous time in the study area. Instead, it may indicate increased summer monsoon rainfall in Northeast China during the time comparable to the Medieval warm period of Europe. The general summer warming over Eurasia relative to the oceans during the period is assumed to be the cause for the strengthened monsoon circulation and increased rainfall in the temperate monsoon area of East Asia.
Dayside auroral hydrogen emission as an aeronomic signature of magnetospheric boundary layer processes
Authors: Deehr C. S. , Lorentzen D. A. , Sigernes F. , Smith R. W.
Published: February 2004

Doppler spectral profiles of dayside auroral hydrogen show sudden increases in precipitating proton energy by a broadening of the spectral profile towards shorter wave‐lengths. This coincides with the equatorward motion of the dayside aurora. A model of the expected spectral character and spatial distribution of the H emission shows that the H emission spectrum is a direct measure of the reconnection process at the dayside magnetopause, i.e., 1) the narrow, symmetric spectral profiles are a measure of the magnetospheric “velocity filter”, 2) the sudden spectral shift of the H emission profiles reflect changes of ion energy due to an increase in the rate of reconnection, 3) spectral H emission observations could be used to map the spatial distribution of the precipitating ion energy, the total reconnection rate, the reconnection sites on the magnetopause, and the direction and intensity of convection.
First gaseous ion composition measurements in the exhaust plume of a jet aircraft in flight: Implications for gaseous sulfuric acid, aerosols, and chemiions
Authors: Arnold F. , Wohlfrom K.‐H. , Klemm M. W. , Schneider J. , Gollinger K. , Schumann U. , Busen R.
Published: February 2004

Mass spectrometric composition measurements of gaseous negative ions have been made in the exhaust plume of a commercial jet aircraft (Airbus A310) in flight at altitudes around 10.4 km and at two plume ages around 3.0 and 3.6 s. Negative ions observed inside the exhaust plume are mostly NO3−(HNO3)m and HSO4−(HNO3)m with m ≤2. Outside the plume in the “background” atmosphere the same negative ion species with the same R = (HSO4−(HNO3)m)/(NO3−(HNO3)m) were observed. This indicates that the ions observed in the plume were entrained ambient atmospheric ions. By contrast no indications for negative chemiions (with masses ≤1100 amu) produced by the airbus engines were found in the plume. Furthermore our measurements indicate a modest decrease of the total concentration of entrained negative ions in the plume compared to the ambient atmosphere outside the plume. This decrease may be due to ion‐removal by ion‐attachment to aerosol‐particles and/or ion‐recombination with positive chemiions. We propose that the observed entrained ions can serve as probes for important plume components including gaseous sulfuric acid, aerosol particles and chemiions. Making use of this analytical potential we infer upper limits for the gaseous sulfuric acid concentration, total aerosol surface area density, and positive chemiion concentration. We conclude that initially formed gaseous sulfuric acid must have experienced rapid gas‐to‐particle conversion already in the very early plume at plume ages < 1.6 s.
Hydroxyl‐radical formation in the gas‐phase ozonolysis of 2‐methylbut‐2‐ene
Authors: Marston G. , McGill C. D. , Rickard A. R.
Published: February 2004

Relative rate constants have been measured for the reactions of eight pairs of organic compounds with the reactive species formed in the reaction of ozone with 2‐methylbut‐2‐ene. A total of eight compounds were studied, including three alkanes, two alkenes, two conjugated alkenes and one aromatic hydrocarbon. With the exception of one pair of compounds (cyclohexane/2‐methylpropane), the relative rate constants obtained are consistent with the assumption that the reactive intermediate is the hydroxyl radical, OH. The origin of the anomalous result for the cyclohexane/2‐methylpropane pair is not clear.
melting of the Siberian Mantle Plume
Authors: Basu Asish R. , Hannigan Robyn E. , Jacobsen Stein B.
Published: February 2004

The Putorana basalts, comprising ∼90% of the Siberian Traps (ST), have had their chemistry modified from primary tholeiitic picritic magmas by ∼12% crystallization of olivine. Major‐trace element ratios, and Nd isotopes of these lavas are consistent with their origin from a relatively undepleted plume by 12–16% rapid decompressional melting at ∼50–80 km depths within the lithosphere.
Observations of highly nonlinear internal solitons over the continental shelf
Authors: Stanton T. P. , Ostrovsky L. A.
Published: February 2004

Surface disturbances caused by strong, near‐surface internal waves are widely seen in coastal regions as bands of slick and rough water propagating shoreward. These surface slicks are typically manifestations of optical and radar backscatter properties above internal solitons, and have strong surface current pulses associated with them. During a recent experiment studying coastal internal waves, extremely strong solitary internal wave packets were observed over a three week period on a very shallow and strongly stratified pycnocline off Northern Oregon. During periods of strongest tidal forcing, solitons were consistently observed on the leading edge of a semidiurnal internal tide bore, with pycnocline displacements up to 25m downward from a 7m initial depth in the first few solitons. The extreme nonlinearity of these internal waves is believed to be unique in ocean observations. This note characterizes these highly nonlinear Solitary Internal Waves (SIW) and presents a second order KdV model which reproduces the form of the displacements, and the small change in soliton width with amplitude predicted by this model.
Porosity/formation‐factor relationships for high‐porosity siliciclastic sediments from Amazon Fan
Authors: Erickson Stephanie N. , Jarrard Richard D.
Published: February 2004

The electrical resistivity of siliciclastic rocks is a function both of pore‐fluid resistivity and of formation factor (FF), an intrinsic rock property. For low‐porosity rocks, FF depends on clay conduction and porosity. In contrast, we find that FF of high‐porosity sediments (fractional porosities of 0.3–0.6) from Amazon Fan is controlled primarily by porosity and pore geometry; clay conduction is a minor effect. Porosity vs. formation factor (FF) plots for Amazon Fan well logs demonstrate two distinct trends which are dependent on the amount of shale present. Muds, with more than about 0.4 shale fraction, follow a trend that increases to much higher FF as porosity decreases, compared to sands and slightly muddy sands. This separation is of opposite sign to the separation between low‐porosity sandstones and shales attributable to clay conduction. We conclude that in high‐porosity muds, presence of clays reduces formation conductivity by increasing the tortuosity of pores.
modeling of the February 1996 Peruvian Tsunami
Authors: Heinrich Philippe , Schindele François , Guibourg Sandrine , Ihmlé Pierre F.
Published: February 2004

The February 1996 Peruvian earthquake generated a larger tsunami than expected from its surface magnitude. This discrepancy as well as the long rupture duration indicate that this event is a ‘tsunami earthquake’. The associated tsunami was strong locally with runup heights of 1 to 5 meters along a coastline of 400 km. It is shown that this tsunami can be modeled for a seismic moment of 2.1020 Nm, using a rigidity of 2.1010 N/m². The tsunami propagation is modeled solving long wave equations by a finite difference method. The maximum run‐up heights in the region of Chimbote can be simulated using a grid increment of 10 meters. The propagation of this small tsunami across the Pacific Ocean is modeled taking into account frequency dispersion. The only notable amplification occurred in the Marquesas Islands where wave heights of 2 meters were observed and are simulated.
Jakobshavn Glacier, west Greenland: 30 years of spaceborne observations
Authors: Sohn Hong‐Gyoo , Jezek Kenneth C. , van der Veen C. J.
Published: February 2004

Early 1960's reconnaissance satellite images are compared to more recent image and map data in an interannual and seasonal study of West Central Greenland margin fluctuations. From 1962 to 1992, ice sheet margins to the north and south of Jakobshavn Glacier retreated despite a decline in average summer temperatures. The retreat may be reversing along the southern flank of the ice stream where regional mass balance estimates are positive. From 1950 to 1996, the terminus of Jakobshavn Glacier seasonally fluctuated ∼2.5 km around its annual mean position. The total calving flux during the summer is more than six times that during winter. We identified that summer melting and the break‐up of sea ice and icebergs in the fjord are important in controlling the rate of iceberg production. If correct, calving rates may be expected to increase should climate become warmer in the near future.
Correlations of stratospheric abundances of CH4 and N2O derived from ATMOS measurements
Authors: Michelsen H. A. , Manney G. L. , Gunson M. R. , Rinsland C. P. , Zander R.
Published: February 2004

ATMOS measurements made over a wide range of altitudes and latitudes demonstrate compact correlations between mixing ratios of CH4 and N2O. Tight but distinct correlations are observed for the tropics, the springtime Arctic vortex, and the extra‐tropics/extra‐vortex regions, indicating dynamical isolation between these regions. Little variability is apparent in correlations between [CH4] and [N2O] from measurements made in different years (1992, 1993, and 1994), seasons (March/April and November), and hemispheres.
Faulting in vertically inhomogeneous media and its geophysical implications
Authors: Rybicki Kacper R. , Yamashita Teruo
Published: February 2004

Faulting of strike‐slip type in vertically inhomogeneous media is analyzed using the classical fracture theory. The analysis makes it possible to get a better insight into various aspects of faulting and earthquakes in real media. The major conclusions are that both low rigidity media and those with regions in which a rapid transition from high to low pore pressure occurs may form barriers for a propagating rupture. The permanent deficit of the driving stress (small or negative stress drop) in sediments that represent the most distinguished class of such media may be one of the main reasons of the generally observed lack of seismicity and rupture suppression there.
Lithospheric seismic velocity discontinuities beneath the Arabian Shield
Authors: Sandvol Eric , Seber Dogan , Barazangi Muawia , Vernon Frank , Mellors Robert , Al‐Amri Abdullah
Published: February 2004

We determined crustal and lithospheric mantle velocity structure beneath the Arabian Shield through the modeling of receiver function stacks obtained from teleseismic P waves recorded by the 9 station temporary broadband array in western Saudi Arabia. The receiver function deconvolution technique was used to isolate the receiver‐side PS mode conversions. A grid search method, which should yield an unbiased global minimum, was used to solve for a shear wave velocity model that is optimal and has the minimum number of layers needed to fit the receiver function waveform. Results from this analysis show that the crustal thickness in the shield area varies from 35 to 40 km in the west, adjacent to the Red Sea, to 45 km in central Arabia. Stability tests of each solution indicate that the models are relatively well constrained. We have also observed evidence for a large positive velocity contrast at sub‐Moho depths at four stations at depths of 80 to 100 km. This discontinuity may represent a change in rheology in the lower part of the lithosphere or remnant structure from the formation of the Arabian Shield.
UV refractive indices of aqueous ammonium sulfate solutions
Authors: Beyer Keith D. , Ebeling Daniel D.
Published: February 2004

Refractive indices of aqueous solutions of ammonium sulfate were measured over a wavelength range of 240 to 400 nanometers (nm) at a temperature of 292 K. The solutions examined cover a broad range from the saturation concentration of ammonium sulfate in water at 292 K down to low concentrations. Solutions studied were: 42.5, 30.4, 23.6, 16.3, 8.5 weight per cent ammonium sulfate. Optical field measurements of these aerosols require knowing the necessary optical constants, and these constants in the ultraviolet (UV) are given here. Our results were found to be in agreement with literature values at longer wavelengths. Additionally, a Lorentz‐Lorenz analysis is presented to extend our results to other wavelengths and temperatures.
Streaming electrical potential anomaly along faults in geothermal areas
Authors: Revil A. , Pezard P. A.
Published: February 2004

Electrical potential anomalies are often measured associated with geothermal areas and volcanoes. In these systems, fluid flow is usually mostly restricted to faults and fracture networks. An equation describing electrical potential anomalies of electrokinetic nature associated with fluid upflow induced by a thermal source along faults is derived. The electrical potential anomaly is related to the depth of the thermal reservoir, the temperature difference between the surface and the reservoir of the geothermal area, the thermal expansion of water, and the streaming electrical potential coupling coefficient in the fault zone. A quantitative calculation of the electrokinetic anomaly is provided by comparing this model to a self‐potential survey of the Cerro‐Prieto geothermal field [Fitterman and Corwin, 1982]. The predictions of the model agree well with the field measurements.
PHAZE II observations of lower hybrid burst structures occurring on density gradients
Authors: McAdams K. L. , LaBelle J. , Schuck P. W. , Kintner P. M.
Published: February 2004

PHAZE II sounding rocket observations of VLF waves and plasma density measurements made with a HF wave instrument rather than a fixed bias Langmuir probe show conclusively that the observed lower hybrid solitary structures (LHSS) are associated with density fluctuations. LHSS occur on the positive and negative gradients of plasma density fluctuations of 25–50%. These findings lend support to theories of ambient lower hybrid waves exciting resonances created by pre‐existing density gradients rather than wave collapse or refraction mechanisms; the issue of how the gradients are created is still unresolved.
The dayside auroral zone as a hard target for coherent HF radars
Authors: Milan S. E. , Yeoman T. K. , Lester M.
Published: February 2004

Observations from the CUTLASS Finland coherent HF radar on 23 February 1996 are employed to demonstrate that changes in propagation mode from ½F to 1½F and back again, determined from elevation angle measurements, do not significantly alter the ranges over which ionospheric backscatter is observed. This indicates that the latitudinal extent of backscatter in the dayside auroral oval and cusp region correspond to the boundaries of geophysical processes, as opposed to limits in the illumination of the F region ionosphere by the radar. Hence, the HF radar technique is confirmed as an excellent diagnostic of the cusp and other dayside regions.
Theoretical and simulation studies of broad up‐shifted sideband generation in ionospheric stimulated radiation
Authors: Hussein A. A. , Scales W. A. , Huang J.
Published: February 2004

A second order four‐wave parametric process proposed to be responsible for the generation of the broad up‐shifted sideband in ionospheric stimulated radiation is studied by using a theoretical model and one dimensional electrostatic particle‐in‐cell simulations. The results indicate that (1) the initial evolution in nonlinear simulations is well described by the proposed theoretical model, (2) the simulation frequency power spectrum in a saturated nonlinear state exhibits important characteristics of the experimental observations and (3) the full nonlinear evolution of this four‐wave process is crucial in interpreting the asymmetric nature of the wave frequency spectrum observed during experiments.