bluuebunny/crossref_metadata_2025 huggingface dataset:
A weaker solar wind termination shock
Authors: Isenberg Philip A.
Published: February 2004

In a recent analysis of anomalous cosmic ray spectra during 1994, Stone et al. [1996] derived a position and compression ratio for the solar wind termination shock of R ≈ 85 AU and ndownstream/nupstream ≈ 2.6, respectively. This compression ratio indicates a fairly weak shock, with Mach number M ≈ 2.4 if the magnetic field can be ignored. Such a weak shock so close to the Sun is difficult to reconcile with the standard picture of the outer heliosphere, which includes an inflowing hydrogen gas of density N = 0.06–0.08 cm−3. However, a consensus has been building for a higher hydrogen density, and Gloeckler [1996] estimates this value at N0=0.125±0.015 cm−3. We show that this new value of the inflowing hydrogen density can yield a solar wind Mach number near 85 AU which is low enough to match the claims of Stone et al.
The global impact of human activity on tropospheric ozone
Authors: Levy H. , Kasibhatla P. S. , Moxim W. J. , Klonecki A. A. , Hirsch A. I. , Oltmans S. J. , Chameides W. L.
Published: February 2004

Within a conceptual framework of stratospheric injection, CO‐CH4 background tropospheric chemistry, parameterized pollution production in the continental boundary layer and surface deposition, we use an 11 level GCTM to simulate global distributions of present and pre‐industrial tropospheric O3. The chemistry is driven by previously simulated present and pre‐industrial NOx fields, while prescribed fields of CO, CH4 and H2O are held constant. An evaluation with measurements from 12 surface sites, 21 ozonesonde sites and 1 aircraft campaign finds agreement within ±25% for 73% of the observations while identifying systematic errors in the wintertime high‐latitude Northern Hemisphere (NH), the Southern Hemisphere (SH) tropics during biomass burning, and the remote SH. We predict that human activity has increased the annual integral of tropospheric ozone by 39% with 3/4's of that increase in the free troposphere, though the boundary layer [BL] annual integral has increased by 66%. The 2 largest components of the global O3 budget are stratospheric injection at 696 TgO3/yr, and loss through dry deposition, which increases from 459 TgO3/yr to a present level of 825 TgO3/yr. While tropospheric chemistry's net contribution is relatively small, changing from a pre‐industrial destruction of −236 TgO3/yr to a present production of +128 TgO3/yr, it is a balance between two much larger terms, −558 TgO3/yr of destruction in the background troposphere and +686 TgO3/yr of production in the polluted boundary layer. Human impact on O3 predominates in the summertime extratropical NH and in the tropics during their biomass burning seasons [increases of 50%–100% or more]. Conversely, there has been little increase in most of the upper troposphere [<20%], where ozone's influence on tropospheric climate is strongest.
Delineation of surfaces by skeletonization: Application to interpretation of 3D seismic reflection and georadar data volumes
Authors: Vasudevan Kris , Tozser Peter , Cook Frederick A.
Published: February 2004

A new 3‐D skeletonization technique based on a four‐cycle correlation allows automatic event detection and mapping of surfaces in any 3‐D volume of reflection seismic data. Interpretation results are comparable to those derived using conventional 3‐D interpretation packages. Furthermore, a product of skeletonization is a surface file containing a variety of seismic attributes for each identified surface that can be accessed for detailed statistical analysis.
Dehydration and sedimentation of ice particles in the Arctic stratospheric vortex
Authors: Vömel H. , Rummukainen M. , Kivi R. , Karhu J. , Turunen T. , Kyrö E. , Rosen J. , Kjome N. , Oltmans S.
Published: February 2004

Balloon borne frost‐point hygrometers and backscatter sondes were launched at Sodankylä, Finland in January and February of 1996. These instruments measure water vapor and the backscatter ratio of light due to polar stratospheric clouds in the Arctic stratospheric vortex. Here we report the results of a hygrometer sonde and a backscatter sonde launched within 3.5 hours of each other on January 22/23. Together these soundings show a strong loss of water vapor due to the formation of ice clouds as a result of record cold temperatures in the Arctic stratosphere. The separation of the upper edge of the layer showing water vapor loss and the upper edge of the PSC layer indicates sedimentation of the ice particle layer, possibly leading to a permanent dehydration in the upper part of the layer exhibiting water vapor loss.
Similarity of waves in dispersive media
Authors: Arzner K. , Bebie H.
Published: February 2004

In a previous letter, D.A.Gurnett [1995] discussed the remarkable fact that atmospheric whistlers propagate under the same emission cone relative to the earth's magnetic field as bow waves do with respect to the ship's velocity—namely under 19°28′. The present contribution is a comment on Gurnett's letter and considers a prerequisite for the occurence of the similarity of both phenomena: the independence of the wave features of parameters such as the ship's speed or the earth's magnetic field. It is found that media with dispersion relations of the form ω ∼ kα show such independence; a more general solution is also given.
Venus resurfacing by coronae: Implications from impact craters
Authors: DeLaughter John E. , Jurdy Donna M.
Published: February 2004

Coronae, common volcano‐tectonic features on Venus, may be actively modifying the planet's surface. To evaluate the extent of their effects, we compare impact crater densities and proportions of modified craters out to four radii for Monte Carlo simulations of corona location with those for two corona classes. We study the Radial Concentric and Concentric Caldera coronae, the two classes believed to represent the youthful and senescent stages of formation, respectively. A high proportion of tectonized craters and low crater density near Radial Concentric coronae indicate recent activity. Based on the average crater density and proportion of tectonized craters, we interpret Concentric Caldera coronae as old. These results show that tectonism and volcanism is not limited to the corona interior and can extend up to four radii from the center.
Tidally induced Sagnac signal in a ring laser
Authors: Rautenberg Volker , Plag Hans‐Peter , Burns Michael , Stedman Geoffrey E. , Jüttner Hans‐Ulrich
Published: February 2004

The Earth rotation vector is an integral dynamical quantity of the Earth system, with Earth rotation variations depending on the overall dynamics of the Earth system at all time scales. New observations of Earth rotation variations with a precision better than 10−9 of the Earth rotation would contribute to the understanding of many geophysical phenomena. High precision short‐term observations of the projection of the Earth rotation vector ΩE on the area vector A of a ring laser are now possible. Tidally induced Sagnac effects are due to changes in the ring geometry (areal strain and perimeter variations), changes in the normal vector of the ring laser plane (tilt), and the vorticity of the Earth's tidal deformations. Here we estimate the latitude‐dependent effect of the Earth's body tide deformations due to vorticity and tilt. At mid‐latitudes, the vorticity δΩ is of the order 8 · 10−8ΩE, but because it is in the local horizontal plane, it is not detectable by a horizontal ring. The Sagnac effect due to tidal tilt for a horizontal ring at mid‐latitudes is of the order of 4 · 10−8 of the Earth rotation effect. Thus, the tidal signal is of an order of magnitude where it may be used for validation of existing and future ring lasers.
Observations of a current pulse in the near‐Earth plasma sheet associated with a substorm onset
Authors: Frank L. A. , Paterson W. R. , Kokubun S. , Yamamoto T. , Lepping R. P. , Ogilvie K. W.
Published: February 2004

The onset of an isolated magnetospheric substorm occurred at about 0437 UT on 9 February 1995 while the Geotail spacecraft was located in the premidnight sector at a geocentric radial distance of about 30 RE. The onset occurred during a slow northward turning of the interplanetary magnetic field after a period of weakly southward fields as observed by the Wind spacecraft upstream from Earth's bow shock. For several minutes immediately following the onset of the substorm an intense field‐aligned current, with maximum current densities of 30 nA/m², was observed at the Geotail spacecraft. This is the first report of a directly detected current pulse coincident with onset. Unlike most of the magnetotail field‐aligned currents which are carried primarily by electrons, this impulsive current at onset is carried by both electrons and protons. It is possible that the onset current pulse is a signature of a “trigger” mechanism for the subsequent expansion phase of a substorm.
Dimethylsulfide (DMS) in the equatorial Pacific Ocean (1982 to 1996): Evidence of a climate feedback?
Authors: Bates Timothy S. , Quinn Patricia K.
Published: February 2004

Oceanic dimethylsulfide (DMS) is the major natural source of sulfur to the atmosphere. The equatorial Pacific Ocean is a region of relatively high DMS emissions that persist throughout the year. Measurements from 11 cruises between 1982 and 1996 show that the mean surface seawater DMS concentration in this region (15°N to 15°S) is relatively constant both seasonally and interannually (2.7±0.7 nM). The large interannual variations in oceanic and atmospheric properties associated with El Niño‐Southern Oscillation (ENSO) events appear to have little effect on the concentration of DMS in surface ocean waters.
Evidence for a stagnant plume in the transition zone?
Authors: Vinnik Lev , Chevrot Sébastien , Montagner Jean‐Paul
Published: February 2004

The structure of the mantle transition zone (MTZ) beneath the Pacific ocean is investigated by using Pds waves, converted from P to S from seismic discontinuities at depths d in the receiver region. At stations within the South Pacific superswell, the pulse of P660s is anomalously broad. To explain this effect, we assume that the 660 km phase boundary may present a barrier for a thermochemical plume ascending from the lower mantle. Then the low‐velocity material of the plume accumulates just below this boundary, and forms a large‐scale lens, which broadens the pulse of P660s. The phase boundary is uplifted by heating, but the related travel time anomaly is cancelled by the increased effective width of the transition.
Characteristic vertical wavenumbers for the polar mesosphere
Authors: Hall C. M. , Hoppe U.‐P.
Published: February 2004

By measuring the vertical component of velocity in the height range 70–90 km above Tromsø (69°N, 19°E), with a 1 km height resolution, we are able to estimate vertical wavenumber spectra. From time averages of these spectra we are able to identify characteristic wavenumbers, m*, which in turn, using well‐established theory, may be interpreted in terms of wave energy and energy deposition rate.
Latitudinal structure of the heliospheric current sheet and corotating streams measured by WIND and ULYSSES
Authors: Ho C. M. , Tsurutani B. T. , Arballo J. K. , Goldstein B. E. , Lepping R. P. , Ogilvie K. W. , Lazarus A. J. , Steinberg J. T.
Published: February 2004

All heliospheric current sheet (HCS) crossings and corotating solar wind streams detected by both WIND and Ulysses have been identified. These measurements were made when Ulysses was in its fast latitudinal scan (at a heliocentric radial distance of ∼1.4 AU) and WIND was in the ecliptic plane near the Earth. Instantaneous solar wind velocities are used to map the locations of the HCS crossings and plasma sources back to the solar surface. The HCS crossing locations have been compared with those predicted by the Stanford source surface magnetic field model. In general, both locations correspond closely, but there is an error range up to 25° in heliographic longitude. These discrepancies in the HSC locations may be due to an overly southward displacement (∼6°) in the model. We have also found that six pairs of corotating streams from 11 pairs of candidate streams have the same sources and were detected by both spacecraft at widely separated latitudes. Under an assumption of the absence of temporal variations, a velocity change of ΔV ≈ 750 e−0.38Δθ (km/s/degree) has been determined as a function of the angular distance, Δθ, from the HCS.
Caspian sea level from Topex‐Poseidon altimetry: Level now falling
Authors: Cazenave A. , Bonnefond P. , Dominh K. , Schaeffer P.
Published: February 2004

Tide gauge measurements recorded between 1978 and 1993 indicate that the Caspian sea level (CSL) has been rising at an average rate of ∼12 cm/yr during this 15‐yr time span. Decadal CSL changes are currently attributed to changes in river runoff and effective evaporation. We have analysed three and a half years (from January 1993 through August 1996) of altimeter range data from the TOPEX‐POSEIDON mission over the Caspian sea to estimate temporal variations in the sea level. We show that the Caspian sea level was still rising at a rate of 18.9±0.5 cm/yr between January 1993 and July 1995 and that the northwestern Caspian in the area of the Volga delta was rising faster (by ∼3 cm/yr) than the middle and south Caspian. However, by mid‐1995, the CSL started to drop abruptly, a trend still observed in 1996. The average sea level decrease recorded from mid‐1995 amounts to −24.8±1.4 cm/yr.
Comparison of lidar backscatter with particle distribution and GOES‐7 Data in Hurricane Juliette
Authors: Jarzembski Maurice A. , Srivastava Vandana , McCaul Eugene W. , Jedlovec Gary J. , Atkinson Robert J. , Pueschel Rudolf F. , Cutten Dean R.
Published: February 2004

Measurements of calibrated backscatter, using two continuous wave Doppler lidars operating at wavelengths 9.1 and 10.6 µm were obtained along with cloud particle size distributions in Hurricane Juliette on 21 September 1995 at altitude ∼11.7 km. Agreement between backscatter from the two lidars and with the cloud particle size distribution is excellent. Features in backscatter and particle number density compare well with concurrent GOES‐7 infrared images.
Solar hydrogen Lyman‐α variation during solar cycles 21 and 22
Authors: Tobiska W. Kent , Pryor Wayne R. , Ajello Joseph M.
Published: February 2004

A full‐disk, line‐integrated solar Lyman‐α dataset is presented that spans two solar cycles. The dataset is created partially from AE‐E and SME data that is scaled to the Pioneer Venus Orbiter Ultraviolet Spectrometer (PVOUVS) upwind Lyman‐α sky background data which is converted to a solar surrogate. PVOUVS measurements overlap AE‐E, SME, and UARS observing periods and are calibrated to UARS/SOLSTICE irradiance units at 1 AU. The scaled AE‐E/SME, the SOLSTICE, and the PVOUVS surrogate data in the interim between the satellites collectively form a composite dataset with a quiet sun value of 3.0±0.1 × 1011 photons cm−2s−1 common for three solar minima and a solar maximum value of 6.75±0.25 × 1011 photons cm−2s−1 common to cycles 21 and 22.
Shear wave dispersion and attenuation in fine‐grained synthetic olivine aggregates: Preliminary results
Authors: Tan Ben H. , Jackson Ian , Fitz Gerald John D.
Published: February 2004

Low‐frequency torsional forced oscillation tests have been performed on a fine‐grained olivine polycrystal to determine shear wave dispersion and attenuation. The specimen was a dense hot‐pressed San Carlos olivine aggregate with uniform grainsize of about 50 µm, < 0.1 vol.% of melt and minor amount of hydroxyl (∼100 ppm). Mechanical tests were conducted under 200 MPa hydrostatic pressure, low oscillation frequencies (0.01–1 Hz) and within the linear regime of strain (amplitude < 5 × 10−5). The specimen was first annealed at 1300°C, and subsequently measured at a series of progressively lower temperatures. At 1300°C evidence was obtained of marked viscoelastic relaxation: the shear modulus G is relatively low and strongly frequency‐dependent and the attenuation Q−1 is high (G ∼ 33 GPa, Q−1 ∼ 0.14 for 1 Hz). In the temperature range 1100–1300°C, G depends strongly on temperature with |∂G/∂T| several times greater than the value measured in ultrasonic experiments at MHz frequencies. Q−1 varies with temperature and frequency as Q−1=A0 [ωeE/RT]−n with activation energy for the relaxation rate E=420±30 kJ/mol and exponent n=0.31±0.02. The presence of thermal cracks complicates the interpretation of data obtained at temperatures below 900°C. Grainsize‐sensitive processes may be responsible for much of the observed viscoelastic relaxation. The strong temperature sensitivity of the shear modulus suggests much smaller thermal anomalies than are commonly inferred to be responsible for the variability of seismic wave speeds in the upper mantle.
A new hydrous silicate, a water reservoir, in the upper part of the lower mantle
Authors: Ohtani Eiji , Mizobata Hiroki , Kudoh Yasuhiro , Nagase Toshiro , Arashi Haruo , Yurimoto Hisayoshi , Miyagi Isoji
Published: February 2004

We synthesized a new hydrous silicate in the pressure range from 20 GPa to 24 GPa at 800–1300°C. This phase, named tentatively as phase G, has a hexagonal unit cell, a=4.790 (3) Å and c=4.344 (3) Å, and V=86.3 (2) Å³ and the atomic ratio Mg/Si=0.66±0.03. SIMS analysis revealed that it contains 14.5±2.0wt% water. Phase G has a chemical formula of Mg1.14Si1.73H2.81O6 and a density of 3.37g/cm³. Phase G coexists with periclase and Mg‐perovskite under the lower mantle conditions, and thus it can be a reservoir of water in cold slabs penetrating into the lower mantle.
Detection of SO2 on Callisto with the Hubble Space Telescope
Authors: Noll Keith S. , Johnson Robert E. , McGrath Melissa A. , Caldwell John J.
Published: February 2004

We have detected SO2 in ultraviolet spectra of Callisto obtained with the Hubble Space Telescope's Faint Object Spectrograph. An absorption band centered at 280 nm appears in the spectrum of Callisto's leading hemisphere, but is not apparent in the spectrum of the trailing hemisphere. The band is similar to the SO2 band on Europa's trailing hemisphere. Callisto's leading hemisphere spectrum can be well fit with models that include SO2 ice absorption with N(SO2) ≥ 6 × 1016 cm−2. Callisto's leading hemisphere is modified by impacts with micrometeorites; this may directly or indirectly be a source of sulfur dioxide.
Electrostatic instability in the central lunar wake: A process for replenishing the plasma void?
Authors: Farrell W. M. , Kaiser M. L. , Steinberg J. T.
Published: February 2004

We report on the WIND observations and subsequent analysis of electrostatic ion beam driven waves in the central lunar wake. Previous reports indicate that ion beams are present in the central lunar wake, these generated by an ambipolar electric field near the wake flanks. We demonstrate that these ion beams are inherently unstable, and thus they are capable of generating the observed broadband electrostatic noise. The beam disruption process may be a dominate mechanism to replace ions in the void trailing the moon. This picture of the wake, with an extended electrostatic tail in the central region is distinctly different from the MHD wake picture discussed previously.
Balloon‐borne measurements of stratospheric radicals and their precursors: Implications for the production and loss of ozone
Authors: Osterman G. B. , Salawitch R. J. , Sen B. , Toon G. C. , Stachnik R. A. , Pickett H. M. , Margitan J. J. , Blavier J.‐F. , Peterson D. B.
Published: February 2004

Measurements of hydrogen, nitrogen and chlorine radicals from a balloon flight on 25 September 1993 from Ft. Sumner, NM provide an opportunity to quantify photochemical production and loss of stratospheric ozone. Ozone loss rates determined using measured radical concentrations agree fairly well with loss rates calculated using a photochemical model. Catalytic cycles involving OH and HO2 are shown to dominate photochemical loss of ozone for altitudes between 44 and 50 km. Reactions involving NO and NO2 are the dominant sink for ozone between 25 and 38 km. The total ozone loss rate determined from the measurements balances calculated production rates for altitudes between 30 and 40 km. However, loss of ozone exceeds production by ∼35% between 42 and 50 km. The imbalance between production and loss of ozone above 42 km is larger than the uncertainty of any one of the critical kinetic parameters or species concentrations. No single adjustment to any of these parameters can simultaneously resolve the imbalance and satisfy constraints imposed by measured OH, HO2, NO2 and ClO. Our results are consistent with an additional mechanism for ozone production above 40 km other than photolysis of ground state O2.
Two day wave induced variations in the oxygen green line volume emission rate: WINDII observations
Authors: Ward W. E. , Solheim B. H. , Shepherd G. G.
Published: February 2004

Variations in the oxygen green line emission rate (at 5577 Å) which correspond to a two day wave signature were observed from January 20 to January 30, 1993 by the Wind Imaging Interferometer (WINDII) on the Upper Atmosphere Research Satellite (UARS). The latitude and height extent of these emission variations are summarized. From the volume emission rate data, fields of oxygen mixing ratio using Mass Spectrometer and Incoherent Scatter (MSIS) model data as the background atmosphere were calculated. Analyses of the mixing ratio fields show the variations of emission rate to be primarily the result (to first order) of vertical motions associated with the quasi two day wave (QTDW), not mixing events associated with wave breaking. The mean peak‐to‐peak amplitude of the vertical displacement is of the order of 1 km although at times this amplitude is as much as 4 km. The phase of the mixing ratio variations approaches the two day wave zonal wind phase above 100 km as is expected from simple considerations of the phase relationships associated with planetary waves and the lifetime of atomic oxygen.
Observations of tidal temperature and wind perturbations in the mesopause region above Urbana, IL (40°N, 88°W)
Authors: Yu Jirong , States Robert , Franke Steve J. , Gardner Chester S. , Hagan Maura
Published: February 2004

Na lidar and MF radar measurements of temperature and horizontal winds were conducted simultaneously during several continuous 24 h periods in March and April 1996 at the Urbana Atmospheric Observatory. The data are used to determine the amplitude and phase profiles of the 24 and 12 h tides in the mesopause region between about 82 and 100 km. The measured amplitudes and phases of the tidal components of the horizontal winds are generally consistent with the predictions of the global‐scale wave model (GSWM). The measured 24 h temperature amplitude is comparable to the GSWM predictions between 85 and 96 km but is significantly larger than GSWM above 96 km. The measured phase progression is downward below 94 km with an inferred vertical wavelength of 14±1 km. Above 94 km the temperature phase progression is upward with a vertical wavelength of 12±1 km. The measurements suggest the presence of a diurnal heat source in the lower thermosphere which is generating a strong downwardly propagating 24 h wave.
A climate predictability index and its applications
Authors: Rangarajan Govindan , Sant Dhananjay A.
Published: February 2004

In this letter, a climate predictability index is proposed. It quantifies the predictability of three major components comprising the climate—temperature, pressure and precipitation. The quantification is done using a fractal dimensional analysis of the corresponding time series. The climate predictability index is calculated for 25 stations spread throughout India using the Global Historical Climatology Network dataset. Change in the index with the seasons suggests a strong influence of more than one climatic dynamics. In such cases, calculations done using mean yearly data are suspect. The index is shown to be useful in studying the interplay between various climatic components (viz. temperature, pressure and precipitation). Changes in predictability indices for temperature and pressure are seen to affect the index for precipitation. The index can be used as a discriminant for determining which stations are selected for use in developing regional climatic models.
Radar evidence for a new low‐frequency crossed‐field plasma instability in the polar mesopause region: A case study
Authors: Tsunoda Roland T. , Olesen Jens K. , Stauning Peter
Published: February 2004

Dimant and Sudan [1995] have recently described a new plasma instability that is excited in the lower ionosphere when a large electric field is applied. This mechanism is intriguing because it is the only low‐frequency plasma process that is capable of generating field‐aligned irregularities (FAI) at altitudes below 90 km. Thus far, the only evidence for its validity has come from a single in situ measurement by rocket [Blix et al., 1996]. In this paper, we show that a southward‐viewing 12.3‐MHz radar can be used to probe the D region for the presence of FAI. We show, from a case study, that the Doppler spectra of radar backscatter from southerly azimuths, obtained under appropriate ionospheric conditions, did contain a spectral component that could be associated with this new instability. This low‐Doppler‐shifted spectral component was accompanied by type‐1 echoes that were produced by the well‐known modified two‐stream instability around an altitude of 95 km.
Braking of high‐speed flows in the near‐Earth tail
Authors: Shiokawa K. , Baumjohann W. , Haerendel G.
Published: February 2004

We have studied possible braking mechanisms of high‐speed ion flows in the near‐Earth central plasma sheet for radial distances between 9 and 19 Earth Radii (RE) on the basis of observations made by the AMPTE/IRM satellite. Flows with velocities in excess of 400 km/s are almost always Earthward for this range, indicating that the source of the flows is beyond 19 RE. Though the occurrence rate of the high‐speed flows substantially decreases when the satellite comes closer to the Earth, high‐speed flows with velocities higher than 600 km/s are still observed. We suggest that the high‐speed flows are stopped at a clear boundary between the regions of dipolar field and tail‐like field in the plasma sheet. The boundary corresponds to the inner edge of the neutral sheet. The average jump of the magnetic field at the boundary, which is estimated from the observations by assuming a pressure balance, is 6.7 nT. The inertia current caused by the braking of the flow and the current caused by pileup of the magnetic flux at the stopping point are quantitatively estimated and discussed in relation to the formation of the substorm current wedge.
Aerosol invariance in expanding coagulating plumes
Authors: Turco Richard P. , Yu Fangqun
Published: February 2004

We demonstrate that the total number of particles in an evolving aerosol plume is limited in a predictable way by the competing rates of coagulation and atmospheric dispersion, and is generally independent of the details of particle nucleation or growth. Using a simplified phenomenological model, expressions are derived from which the time variation in the total number of aerosols generated by localized sources can be calculated, as can their size distribution and local concentrations. Consideration of various microphysical processes contributing to aerosol plume development leads to the conclusion that the potential nucleation of enormous numbers of fine particles (for example, in high‐altitude aircraft wakes and volcanic eruption clouds) does not affect the total number eventually dispersed throughout the atmosphere. We show that, after a suitable period of time (which is quite short relative to the time scales of regional and global dispersion), the aerosol population (total number, or concentration) is independent of the initial number, and instead depends in a simple way on the average coagulation kernel and plume dispersion rate. In terms of these basic physical parameters, we define a unique dimensionless number that fully determines the time evolution of the aerosol population, and show how this invariant number can be applied to estimate the properties of particulates emitted by high‐altitude aircraft.
Perpendicular ion heating by velocity‐shear‐driven waves
Authors: Walker D. N. , Amatucci W. E. , Ganguli G. , Antoniades J. A. , Bowles J. H. , Duncan D. , Gavrishchaka V. , Koepke M. E.
Published: February 2004

Perpendicular ion heating resulting from velocity‐shear‐driven ion‐cyclotron waves has been measured for the first time. The experiment was performed in the Naval Research Laboratory's Space Physics Simulation Chamber (SPSC) under plasma conditions approaching those in the natural space environment. Sheared cross‐field flow is induced by a controllable, inhomogeneous, transverse, DC electric field (LE ∼ (1–2)ρi) created without drawing significant levels of magnetic‐field aligned current. Mode frequency data suggest that the most efficient heating occurs when the Doppler shifted frequency in the ion frame is located near a harmonic of the ion‐cyclotron frequency.
Mid‐latitude observations of the seasonal variation of BrO 1. Zenith‐sky measurements
Authors: Aliwell S. R. , Jones R. L. , Fish D. J.
Published: February 2004

Zenith‐sky observations of the seasonal evolution of BrO slant columns above Aberdeen (57°N) between November 1994 and April 1995 are presented. The measurements show maximum differential BrO slant columns (90°–81°) of 2.4 × 1014 molecules cm−2 in January, decreasing to 1 × 1014 in spring. On a seasonal timescale, BrO slant columns are anticorrelated with NO2 slant columns, which is qualitatively consistent with BrONO2 being the main nighttime bromine reservoir. There is some evidence for a small (5 × 1013 molecules cm−2) increase in sunrise BrO slant columns inside the polar vortex, following chlorine activation on PSCs, as shown by measurements of large OClO slant columns.
Streamer belt structure at solar minima
Authors: Richardson John D. , Paularena Karolen I.
Published: February 2004

We present plasma data from IMP 8 and Voyager 2 demonstrating the character of the current (1996) solar minimum and compare the current solar minimum to past solar minima. Voyager 2 data from 50 AU and 16°S heliolatitude show a gradual 130 km/s increase in solar wind velocity which reaches a plateau of 580 km/s for 75 days in late 1996. We suggest that this plateau, from which solar rotation signatures are absent, consists of solar wind which originated at the Sun at the time of solar minimum. We find that the current solar minimum closely resembles that of the 1976 solar minimum; both are characterized by relatively thick streamer belts. During the 1986–87 solar minimum the streamer belt was only half as thick (∼8°) as in 1976 and 1996. This suggests a possible 22‐year cycle in solar wind characteristics and we predict that at the next solar minimum in about 2007 the streamer belt will again be very thin.
Galileo measurements of plasma density in the Io torus
Authors: Bagenal F. , Crary F. J. , Stewart A. I. F. , Schneider N. M. , Gurnett D. A. , Kurth W. S. , Frank L. A. , Paterson W. R.
Published: February 2004

The measurements of electron density made by the Plasma Wave Subsystem instruments on Galileo during its pass through the torus on December 7th, 1995 are compared with a model based on Voyager 1 measurements made in March 1979. Outside Io's orbit, the plasma densities observed by Galileo are approximately a factor of two higher than the Voyager values. Shortly after crossing Io's orbit, the Galileo density profile dropped sharply and remained at low values for the rest of the inbound leg, suggesting that the ‘ribbon‧ region was either absent or much farther from Jupiter than usual. The peak density on the outbound leg is consistent with Voyager‐based predictions for the cold torus in both location (5.1 Rj) and magnitude (950 cm−3). Inside 5 Rj the density dropped sharply to less than 3 cm−3.
Imaging 3‐D spherical convection models: What can seismic tomography tell us about mantle dynamics?
Authors: Mégnin Charles , Bunge Hans‐Peter , Romanowicz Barbara , Richards Mark A.
Published: February 2004

We assess whether current global seismic tomography can resolve parameters characterizing mantle dynamics, in particular 1) a viscosity increase from the upper to the lower mantle, 2) an endothermic phase transition at the 670 km discontinuity, 3) heat flux across the core‐mantle boundary and 4) the effect of the motion of rigid surface plates on the convection planform. We apply a ‘linear seismic filter' to numerical convection models that incorporate the desired physical parameters, assuming that the shear velocity perturbations depend only on the convectively induced temperature variations. We show that the differences between the characteristic spectral patterns of convection models are preserved by the filtering process. Comparison with actual 3D seismic mantle models indicates that the effect of rigid plates dominates the spectral characteristics of the models. We estimate the effect of spatial aliasing of higher order structure into a lower order model, and find that the structure retrieved by inversion is more distorted by the effects of the aliasing than by those due to uneven ray coverage. This effect is strongest at shorter wavelengths and near the core‐mantle boundary. We also find that the proper choice of radial smoothing parameters is crucial for detecting subtle signatures such as that of an endothermic phase transition at the 670 km discontinuity.
The effects of the water flow through the Canadian Archipelago in a global ice‐ocean model
Authors: Goosse H. , Fichefet T. , Campin J.‐M.
Published: February 2004

Numerical experiments are conducted with a global ice‐ocean model in order to evaluate the influence of the water flow from the Arctic Ocean to Baffin Bay through the Canadian Archipelago on the water‐mass properties of the Arctic Ocean and adjacent seas and, more generally, on the global ocean circulation. The results indicate that this flow plays a significant role in controlling the freshwater budget of the Arctic Ocean. When the Canadian Archipelago passage is open in the model, the Arctic pycnocline experiences a noticeable increase in salinity. Furthermore, the flow of relatively fresh Arctic waters through the passage yields a pronounced decrease of surface salinity and density in the Labrador Sea, which leads to a diminution of convective activity there. As a result, the North Atlantic Deep Water outflow in the model is reduced by about 5%. Deep convection in the Norwegian Sea exhibits almost no change, and this despite a weakening of the inflow of relatively fresh Arctic waters through Fram Strait.
A new, temporarily confined population in the polar cap during the August 27, 1996 geomagnetic field distortion period
Authors: Chen Jiasheng , Fritz Theodore A. , Sheldon Robert B. , Spence Harlan E. , Spjeldvik Walther N. , Fennell Joseph F. , Livi Stefano
Published: February 2004

On August 27, 1996, a two‐hour energetic heavy ion event (∼1 MeV) was detected at 8:25 UT at apogee (∼9 Re and an invariant latitude of ∼80°), by the Charge and Mass Magnetospheric Ion Composition Experiment onboard POLAR. The event, with a maximum spin averaged peak flux of ∼150 particles/(cm²‐sr‐s‐MeV), showed three local peaks corresponding to three localized regions; the ion pitch angle distributions in the three regions were different from an isotropic distribution and different from each other. No comparable flux was observed by the WIND spacecraft. The appearance of lower energy He++ and O > +2 during the event period indicates a solar source for these particles. From region 1 to 2 to 3, the helium energy spectra softened. A distorted magnetic field with three local minima corresponding to the three He peak fluxes was also observed by POLAR. A possible explanation is that the energetic He ions were energized from lower energy helium by a local acceleration mechanism that preferred smaller rigidity ions in the high altitude polar cusp region.
Topography of the “410” and “660” km seismic discontinuities in the Izu‐Bonin Subduction Zone
Authors: Collier Jonathan D. , Helffrich George R.
Published: February 2004

We study the effects of a subducting lithospheric slab on the “410” and “660” km mantle seismic discontinuities in the Izu‐Bonin region using data collected from networks of vertical component seismometers in the United Kingdom and northwestern United States. The consequences of a phase change origin for these discontinuities is tested by examining the effect of laterally changing temperature in and near the subducting slab. We analyse the data collected from 21 earthquakes with depths between 40 and 548 km. Based on arrival time and slowness we identify reflections and mode conversions in slant stacks with the aim of mapping the “410” and “660” km discontinuities. The combination of UK and US array data permits interrogation of the discontinuity properties on both sides of and also inside the slab. Results indicate a “410” minimum depth of 350 km in the interior of the slab and a “660” maximum depth of 700 km. A phase change origin for the discontinuities is consistent with the effects of lateral temperature changes on discontinuities with Clapeyron slopes of opposite signs. Here we see more topography on the “410” than the “660” consistent with thermodynamic Clapeyron slope estimates. “410” elevation suggests temperatures in the slab of 600±75°C at a depth of 350 km. We see weak evidence for a broader 410 near the slab interior, consistent with expected thermochemical effects.
Elevation of the 410 km discontinuity beneath the central Tien Shan: Evidence for a detached lithospheric root
Authors: Chen Y. H. , Roecker S. W. , Kosarev G. L.
Published: February 2004

We analyzed P‐SV converted phases recorded by the Kyrgyzstan Broadband Network (KNET) to investigate the nature of phase transitions in the upper mantle beneath the central Tien Shan and the Kazakh shield. We find that P‐SV phases from the 410 km discontinuity recorded by several stations located along the range front are about 2 s earlier from beneath the Tien Shan than they are from beneath the Kazach shield. Because the delay times at stations located on the Kazakh shield are normal and seismic velocities in the upper mantle beneath this part of the Tien Shan apparently are low (about 4% less than the Kazakh shield to the north), the early arrival of the conversion from 410 km implies that this discontinuity is elevated by about 20 km. Because the 410 km discontinuity can be elevated by the introduction of cold material, our results are consistent with a model in which the lithosphere in this area developed a root during collision that later detached and is now residing near 410 km depth.
Equatorial disturbance dynamo electric field longitudinal structure and spread F: A case study from GUAR/EITS Campaigns
Authors: Abdu M. A. , Sastri J. H. , MacDougall J. , Batista I. S. , Sobral J. H. A.
Published: February 2004

Digisondes/ionosondes, an HF Doppler radar and magnetometers were operated in Brazil and India during the September/October 1994 GUARA/EITS campaigns. Analysis of the data for the two disturbed intervals, 2–4 October and 25–27 September provided evidence of a longitudinal structure in the disturbance dynamo (DD) electric field at low latitudes. The DD electric field which is westward in the evening, inhibited the developments of the equatorial prereversal electric field and postsunset ESF, whereas the simultaneous eastward field in the predawn sector, did not lead to ESF, contrary to what is normally expected. This nondevelopment of ESF is suggested as evidence of the stabilizing effect of transequatorial neutral winds associated with stormtime circulation. The campaign observations clearly demonstrate that the DD electric fields could often mask the low latitude ionospheric responses to prompt penetration electric fields in the course of sustained substorm activity.
Field aligned currents in the high latitude, high altitude magnetosphere: POLAR initial results
Authors: Russell C. T. , Zhou X.‐W. , Le Guan , Reiff P. H. , Luhmann J. G. , Cattell C. A. , Kawano H.
Published: February 2004

Magnetic field measurements obtained by the POLAR spacecraft are used to map out the region 1 and region 2 field‐aligned current systems in the dayside hemisphere at radial distances of close to 8 Earth radii above the northern polar cap. The extrapolated invariant latitude of these currents is quite variable. The equatorward edge of the region 1 system ranges from 73 to 83° degrees invariant latitude. The sense of both systems reverses across noon as expected. The strength of the currents also varies, averaging about 0.03 A/m for the region 1 currents and 0.01 A/m for the region 2 currents. Over the dayside hemisphere this amounts to about 1.5 million amps flowing down and up the field lines in the region 1 system and about 0.5 million amps in the region 2 system. These numbers and the behavior of the current are quite consistent with low‐altitude observations.
Heliospheric termination shock motion in response to LISM variations: Spherically symmetric model
Authors: Ratkiewicz R. , Barnes A. , Spreiter J. R.
Published: February 2004

The unsteady spherically symmetric one‐dimensional gasdynamic model appears to be a powerful tool in the investigation of the termination shock motion. Such a model has previously been used to examine the response of the heliospheric termination shock to variations in upstream solar wind conditions [Ratkiewicz et al., 1996]. In the current paper we apply the same model to study response of the shock to variations in the interstellar medium. The initial‐boundary conditions for the unsteady calculations are given by the pressure as a function of time on an outer boundary either alone or with the density as a function of time on an inner boundary. The motion of the termination shock is caused by fluctuations in both solar wind and interstellar plasma parameters and has a rather complicated behavior, characterized by a sequence of perturbations that hit the termination shock and are reflected from the outer boundary.
Modeling the Galileo dust measurements at Jupiter
Authors: Horányi Mihály , Grün Eberhard , Heck Andreas
Published: February 2004

We discuss our modeling that is aimed to reproduce the observed dust impact rates during the first two Ganymede encounters of Galileo. We use a detailed fields and particles model of the magnetosphere and simultaneously follow the dynamics and the charging history of small dust particles. We assume Io to be the only source of the escaping dust grains and show that our model matches the gross characteristics of the observations. We argue that the large scale dawn‐to‐dusk electric field can be responsible for shaping the emission pattern of dust from the Io plasma torus. The emission pattern shows a minimum flux toward the Sun, perhaps explaining why the observed fluxes did not increase as Galileo approached the source region of the dust particles. We show that the general shape of the trajectories of the grains offers a good explanation for the sudden shift in the observed direction of the dust impacts. Modeling the observed dust impact rates gives an excellent opportunity to test our particles and fields model of Jupiter's magnetosphere.
Highly collimated electron beams observed during quiet times
Authors: Sugiyama T. , Fujimoto M. , Nagai T. , Mukai T. , Saito Y. , Terasawa T. , Yamamoto T. , Kokubun S.
Published: February 2004

Using 3D particle data from GEOTAIL, we have studied the occurrence of highly‐collimated bidirectional electrons in the magnetotail at −50 ≤ XGSM ≤ −9 Re during quiet intervals. They are found to appear frequently in the near‐Earth plasma sheet (−20 ≤ XGSM ≤ −10 Re), and more frequently on the dawn side than on the dusk side, with the maximum occurrence frequency of about several percentage. Both parallel/anti‐parallel components possess a characteristic flat‐top/bump shaped spectrum, which extends upto several hundreds eV to keV energy range. The balanced fluxes in both directions suggest that the electron beams are bouncing on closed field lines. Although these distribution shapes closely resemble those observed around the geosynchronous orbit and above the auroral zone, whose origins have been attributed to the active auroral acceleration, we report events that are detected in very quiet times (Kp ≤ 1°), which may cast a new question on the auroral processes during quiet intervals.
Quantification of interplate coupling in subduction zones and forearc topography
Authors: Cattin R. , Lyon‐Caen H. , Chéry J.
Published: February 2004

The effect of long term coupling in subduction zones on forearc topography is studied using a 2‐dimensional finite element model. A curved fault, representing the interface between subducting slab and overriding plate, has been incorporated into a model with an elastic crustal layer, a viscoelastic upper mantle, an initial topography and an effective coefficient of friction on the fault. We assume that traction arising from friction is one of the stresses acting on topography. For various friction coefficients, the change of topography after some equilibration time is computed with specific geometry and kinematic boundary conditions for three subduction zones: northern Chile, northern Japan and Tonga. While the intrinsic coefficient of friction for small rock samples is high (µ ∼ 0.6–0.8), the observed topography of forearc regions are inconsistent with an effective friction coefficient larger than 0.2.
The reaction of ClONO2 with HCl on aluminum oxide
Authors: Molina Mario J. , Molina Luisa T. , Zhang Renyi , Meads Roger F. , Spencer Darryl D.
Published: February 2004

The chlorine activation reaction ClONO2 + HCl → HNO3 + Cl2 was investigated in the laboratory on hydroxylated α‐alumina surfaces under reactant partial pressure, humidity, and temperature conditions covering those which are encountered at mid‐latitudes in the lower stratosphere. The measured reaction probability is γ∼ 0.02. This result has implications with regard to the stratospheric impact of launch vehicles utilizing solid‐fuel rocket motors (SRMs), such as the Space Shuttle. The exhaust from SRMs consists of alumina particles and of HCl and other vapors. The reaction probability measured in this work suggests that the ozone depletion potential of SRMs may be higher than that predicted on the basis of the chlorine emissions alone, especially at mid‐latitudes in the lower stratosphere, where catalytic chlorine activation by background sulfuric acid aerosols is very inefficient. The reaction probability on Pyrex glass was found to be similar to that on α‐alumina. The reaction mechanism appears to be determined by the water layers adsorbed on the surface, rather than by the detailed nature of the refractory surface itself.
Fluid flow in fractally rough synthetic fractures
Authors: Glover P. W. J. , Matsuki K. , Hikima R. , Hayashi K.
Published: February 2004

Fluid flow through fractures in rocks depends upon the roughness of the fracture surfaces. In this work the height of both surfaces of a fracture in a core from the Higashi Hachimantai geothermal test field in northern Japan have been measured and analyzed to determine the monofractal behavior of the surfaces and resulting aperture, and the extent of surface matching. We have used these parameters to create synthetic fractures that are extremely good imitations of the measured fracture by using a new technique for controlling surface mismatching. These numerically synthesized fractures have been used in flow modeling by solving Reynolds equation in the three dimensions, and for calculating the transmissivity of the field fracture. The modeled transmissivity showed good agreement with the fracture transmissivity obtained from field pressure tests, and indicates that such an approach is able to estimate larger scale flow through real sub‐surface fractures.