bluuebunny/crossref_metadata_2025 huggingface dataset:
Intermediate‐focus earthquakes under South Shetland Islands (Antarctica'
Authors: Ibáñez J. M. , Morales J. , Alguacil G. , Almendros J. , Oritz R. , Del Pezzo E.
Published: February 2004

This study is based on data from five field surveys (1992–1996' of seismic monitoring on Deception Island (South Shetland Islands, Antarctica'. In the 1994–95 and 1995–96 surveys earthquakes were recorded by a seismic array. In previous surveys data were collected by a high‐dynamic range, short‐period station. The analysis of the events shows evidence of intermediate‐focus seismicity [50 < H< 100 km] related to the underplating zone of the South Shetland plate. Because of poor station coverage we had to use unconventional techniques to locate the events, such as zero lag cross‐correlation method that provide information about apparent velocity and back‐azimuth, ray‐tracing procedure and particle motion patterns. These criteria allowed us to identify 15 earthquakes that could be considered as intermediate‐focus events, for which some focal parameters were estimated. We conclude that the subduction zone between the Drake plate and South Shetland microplate has a moderate level of intermediate‐depth microseismicity.
High‐velocity frictional properties of gabbro
Authors: Tsutsumi Akito , Shimamoto Toshihiko
Published: February 2004

High‐velocity friction experiments have been performed on a pair of hollow‐cylindrical specimens of gabbro initially at room temperature, at slip rates from 7.5 mm/s to 1.8 m/s, with total circumferential displacements of 125 to 174 m, and at normal stresses to 5 MPa, using a rotary‐shear high‐speed friction testing machine. Steady‐state friction increases slightly with increasing slip rate at slip rates to about 100 mm/s (velocity strengthening) and it decreases markedly with increasing slip rate at higher velocities (velocity weakening). Steady‐state friction in the velocity weakening regime is lower for the non‐melting case than the frictional melting case, due perhaps to severe thermal fracturing. A very large peak friction is always recognized upon the initiation of visible frictional melting, presumably owing to the welding of fault surfaces upon the solidification of melt patches. Frictional properties thus change dramatically with increasing displacement at high velocities, and such a non‐linear effect must be incorporated into the analysis of earthquake initiation processes.
Are energetic electrons in the solar wind the source of the outer radiation belt?
Authors: Li Xinlin , Baker D. N. , Temerin M. , Larson D. , Lin R. P. , Reeves G. D. , Looper M. , Kanekal S. G. , Mewaldt R. A.
Published: February 2004

Using data from WIND, SAMPEX (Solar Anomalous, and Magnetospheric Particle Explorer), and the Los Alamos National Laboratory (LANL) sensors onboard geostationary satellites, we investigate the correlation of energetic electrons in the 20–200 keV range in the solar wind and of high speed solar wind streams with relativistic electrons in the magnetosphere to determine whether energetic electrons in the solar wind are the source of the outer relativistic electron radiation belt. Though there is some correlation between energetic electron enhancements in the solar wind and enhancements in the outer radiation belt, the phase space density of 20–200 keV electrons in the solar wind is not adequate to supply the outer radiation belt electrons. Although lower energy electrons in the solar wind could be a seed population of the outer radiation belt, such lower energy electrons cannot achieve relativistic energies through the normal process of radial transport which conserves the first adiabatic invariant. Thus additional internal acceleration processes are required within the magnetosphere to produce the outer radiation belt. High speed solar wind streams are well correlated with increased magnetic activity and with increased fluxes in the outer radiation belt. The maximum correlation between the high speed streams and the radiation belt flux occurs with an increasing time delay for higher energies and and lower L values. We conclude that acceleration processes within the magnetosphere which are well correlated with high speed solar wind streams are responsible for the outer radiation belt electrons.
Effects of surface contamination on fluid flow
Authors: Moerig R. , Waite W. , Spetzler H.
Published: February 2004

Surface contamination effects on fluid flow across a glass surface have been examined in the absence and presence of a fluid meniscus. The flow of water in the absence of a fluid meniscus is unaffected by contamination of the glass surface with propanol. Meniscus motion across a glass surface, however, is affected by surface contamination and demonstrates dissipative stick‐slip behavior. Dissipative meniscus motion and the dependence of meniscus mobility on surface contamination contribute to the attenuation measured in partially saturated artificial glass cracks, and may be an important component of the seismic attenuation in partially saturated rocks.
Constraints on present‐day shortening rate across the central eastern Andes from GPS data
Authors: Leffler Lisa , Stein Seth , Mao Ailin , Dixon Timothy , Ellis Michael A. , Ocola Leonidas , Sacks I. Selwyn
Published: February 2004

Two years of continuous GPS data from several sites in South America indicate that Arequipa in the southern Peruvian Andes has a velocity of 13±3 mm/yr (two standard errors) to the northeast with respect to stable South America. We interpret these data as reflecting a combination of elastic strain accumulation associated with a locked Nazca‐South America subduction zone and a small amount of crustal shortening across the fold and thrust belt on the eastern margin of the Andes. Models of elastic strain accumulation for fully locked and partly locked subduction zones constrain shortening in the eastern Andes to 0–3 mm/yr (fully locked) and 0–12 mm/yr (partly locked), slower than some geologic estimates averaged over millions of years.
Inflation of Long Valley Caldera, California, Basin and Range Strain, and possible mono craters dike opening from 1990–94 GPS surveys
Authors: Marshall Grant A. , Langbein John , Stein Ross S. , Lisowski Michael , Svarc Jerry
Published: February 2004

Five years of annual Global Positioning System (GPS) surveys of a network centered on Long Valley, California, constrain displacement rates for these stations relative to a central station in the network. These observations are consistent with recent models of resurgent dome inflation in Long Valley (Langbein et al., 1995) and have sufficient signal to detect the presence of Basin and Range strain in the Long Valley region. The data also allow for the possibility of dike inflation beneath the Mono Craters; dike intrusion is consistent with the Mono Craters' recent geologic history of ash eruptions, with seismic tomography, leveling data, and geologic studies of these volcanic domes and flows.
A determination of the source of Jovian hectometric radiation via occultation by Ganymede
Authors: Kurth W. S. , Bolton S. J. , Gurnett D. A. , Levin S.
Published: February 2004

During the first Galileo flyby of Ganymede, Jovian radio emissions in the frequency range of 700 kHz to 5.6 MHz were completely occulted by the satellite. We take advantage of this serendipitous observation to determine the location of the radio emission source relative to Jupiter. The evidence suggests that the apparent source is along an L≳7 magnetic field line near the central meridian longitude (∼160°) of the spacecraft and at 1 to 3 Jovian radii above the northern hemisphere of Jupiter. These results are consistent with a source located along either the Ganymede or Europa flux tube.
Measurements of short wavelength VLF bursts in the auroral ionosphere: a case for electromagnetic mode conversion?
Authors: Delory G. T. , Ergun R. E. , Klementis E. M. , Carlson C. W. , McFadden J. P.
Published: February 2004

Intense, localized bursts of VLF emissions were measured on the University of California at Berkeley Alaska '93 auroral sounding rocket. A wavelength determination for these waves was obtained using cross‐spectral analysis on high time resolution electric field measurements from dipole antennas and an onboard burst memory system. The observation of an antenna null in the cross‐spectral response reveals very short wavelength emissions with wavelengths less than 5.5 meters. The applicability of a collapse theory for these emissions is put in question since these examples are not well correlated with electron density depletions. In addition, these waves do not appear to be associated with a particular type of electron distribution which may have been responsible for their generation. The presence of electromagnetic modes in the VLF frequency range in the vicinity of many of these electrostatic bursts, along with continual electron density turbulence of 1–5%, may provide evidence for a linear mode coupling mechanism in which electrostatic VLF waves are produced by the scattering of incident electromagnetic whistlers from electron density irregularities.
LF and MF observations of the lightning electromagnetic pulse at ionospheric altitudes
Authors: Kelley M. C. , Baker S. D. , Holzworth R. H. , Argo P. , Cummer S. A.
Published: February 2004

For the first time the full ionospheric signature of the lightning electromagnetic pulse (EMP) was measured up to a frequency of 2 MHz. At altitudes below 225 km, the upward‐going whistler wave is found to have a nose‐whistler wave shape with the fastest propagating frequency (nose frequency) near 80 kHz. The bulk of the EMP energy is at the nose frequency, and there is a sharp upper limit near 175 kHz where the group delay is very long. We believe the group delay is due to a propagation resonance for the whistler mode (slightly non‐longitudinal propagation) associated with the low plasma frequencies in the F‐layer valley. MF emissions were seen below the F peak, but not above. These results verify earlier speculation that the leading intense edge of the lightning EMP was carried by 50–125 kHz waves. In addition, we present tantalizing evidence for detection of a pulse pair prior to the stroke that is similar to transionospheric pulse pairs (TIPPs) detected in satellite data.
Relation between low latitude insolation and δ18O change of atmospheric oxygen for the last 200 kyrs, as revealed by Mediterranean sapropels
Authors: Mélières M.‐A. , Rossignol‐Strick M. , Malaizé B.
Published: February 2004

The isotopic ratio of atmospheric O2, δ18Oatm, deduced from ice cores, displays large fluctuations during climatic cycles. These are caused principally by changes in the oxygen isotopic ratio of sea‐water, δ18Osw, and changes in the biosphere and in the hydrological cycle. As both δ18Oatm and δ18Osw coincide closely over the last 135 kyr BP, it is generally believed that δ18Oatm is driven mainly by δ18Osw. Here we focus on the major discrepancy, which arises between those two signals during the prior isotopic glacial stage 6, around 175 kyr BP, discrepancy which calls into question the role of changes in δ18Osw as the driving mechanism for δ18Oatm. We present arguments, based on the occurrence and pollen content of Mediterranean sapropels, for another source of the δ18Oatm change: insolation at low latitudes via hydrosphere/biosphere activity.
Time scales and trends in the central England temperature data (1659–1990): A wavelet analysis
Authors: Baliunas Sallie , Frick Peter , Sokoloff Dmitry , Soon Willie
Published: February 2004

We have applied the standard wavelet and the adaptive wavelet transform algorithms to the record of the Central England Temperature (CET) from 1659–1990. Peaks in the CET spectra include 7.5±1.0 yr, 14.4±1.0 yr, 23.5±2.0 yr, as well as a previously unreported variation at 102±15 yr. Our wavelet analysis of CET agrees with previous results from Singular Spectrum Analysis (SSA) by Plaut et al. [1995] and gives additional results of variability on longer timescales. The interdecadal and century‐scale variability in CET is strongly dependent on the interval of analysis. Estimates of a data trend are also shown to be sensitive to the cutoff timescale of the filter. A cooling of ≈ 0.3°C during 1659–1720 is found relative to the temperatures during the 1800s. The complex time dependence of the actual data cautions against using model‐derived representations of natural variability on such long timescales.
Viscoelastic properties of polycrystalline solid methane and carbon dioxide
Authors: Yamashita Yasuyuki , Kato Manabu
Published: February 2004

The viscoelastic properties of polycrystalline solid methane and carbon dioxide were measured in a low‐temperature deformation apparatus. It was found that solid methane flowed easily under a shear stress of 5 MPa even at a temperature of 77 K. Its stress was relaxed with exponent 1.9±0.2 in non‐Newtonian power‐law. The effective viscosity of solid methane estimated at 0.1 MPa was 1011Pa sec. Solid carbon dioxide was deformed brittly at 77 K.
Ionospheric response to an auroral substorm
Authors: Schunk R. W. , Zhu L. , Sojka J. J. , Bowline M. D.
Published: February 2004

The response of the ionosphere to a representative auroral substorm was simulated. The response was found to be significant at all altitudes in a large spatial region near midnight magnetic local time. In this midnight region, there were Te and Ti hot spots, substantial O+ → NO+ composition changes, non‐Maxwellian velocity distributions, transient ion upwellings, a large‐scale lowering of the F‐layer, ionization peaks that occur in the E‐region, and sharp horizontal gradients. Also, during the expansion phase, the E‐region densities increase due to auroral precipitation, while the plasma densities above 300 km decrease due to the overall lowering of the ionosphere. The net result is that the temporal morphologies of the plasma densities at high and low altitudes are opposite during this part of the substorm. These complex features indicate that care must be exercised when interpreting plasma measurements from both ground‐based and space‐based instruments.
Rate constants for the reactions of CO3−(H2O)n=0–5 + SO2: Implications for CIMS detection of SO2
Authors: Seeley John V. , Morris Robert A. , Viggiano A. A.
Published: February 2004

The rate constants for the CO3−(H2O)n + SO2 reactions were measured for n=0–5 using a variable temperature‐selected ion flow tube. Temperature dependences were measured for n=0–3 over the following temperature ranges: n=0, 158–550 K; n=1, 158–270 K; n=2, 158–193 K; n=3, 158–193 K. The n=4, 5 rate constants were measured exclusively at 158 K. Good agreement is found with previous measurements of the n=0 and 1 rate constants. Expressions are estimated for use in chemical ionization mass spectrometric detection of SO2 in the troposphere.
Cross‐equatorially radiating stratospheric Rossby waves
Authors: O'Sullivan Donal
Published: February 2004

Upper Atmosphere Research Satellite observations of constituent distributions in the middle stratosphere show that extratropical Rossby waves from the winter hemisphere can, at certain times, radiate across the equator and reach the summer subtropics before they break and are absorbed. Conditions are most favorable for Rossby waves to radiate into the tropics when the westerlies of the winter hemisphere extend to low latitudes, as usually occurs during November and December in the northern hemisphere. Cross‐equatorial radiation of quasi‐stationary Rossby waves requires westerly equatorial winds, as occurred in the middle stratosphere in late 1992. Constituent distribution maps show numerous episodes of Rossby‐wave radiation across the equator during this early winter period, but not after early January 1993. Wave breaking in both the winter and summer subtropics above 22 mb causes constituent exchange between the tropics and extratropics, including deep tropical in‐mixing.
Observations of anthropogenic inputs of the isoprene oxidation products methyl vinyl ketone and methacrolein to the atmosphere
Authors: Biesenthal Thomas A. , Shepson Paul B.
Published: February 2004

The isoprene atmospheric oxidation products methyl vinyl ketone (MVK) and methacrolein (MACR), along with CO, were measured in Toronto, Ontario in the winter and summer of 1996. These carbonyl compounds were highly correlated with CO in the winter, indicating that they are produced in significant amounts by automotive sources. Regression of the observed MVK and MACR concentrations against CO leads to emission factors relative to CO of 1.4 (±0.3) × 10−4 and 7.3 (±1.6) × 10−5 (mole/mole), respectively. Emission inventories for CO and isoprene allow us to estimate that, for Toronto in the summer, as much as 48 (±30)% of the MVK and 36 (±23)% of the MACR input into the atmosphere is derived from mobile source emissions. This source also has a strong influence on the MVK/MACR ratio, which in this environment remains relatively constant, with values typically ranging between 2.0–2.5. The impact of this is that MVK and MACR mixing ratios are not unambiguous indicators for isoprene chemistry and its impact on ozone production for urban environments.
Thermal models for basaltic volcanism on Io
Authors: Keszthelyi L. , McEwen A.
Published: February 2004

We present a new model for the thermal emissions from active basaltic eruptions on Io. While our methodology shares many similarities with previous work, it is significantly different in that (1) it uses a field tested cooling model and (2) the model is more applicable to pahoehoe flows and lava lakes than fountain‐fed, channelized, 'a'a flows. This model demonstrates the large effect lava porosity has on the surface cooling rate (with denser flows cooling more slowly) and provides a preliminary tool for examining some of the hot spots on Io. The model infrared signature of a basaltic eruption is largely controlled by a single parameter, τ, the average survival time for a lava surface. During an active eruption surfaces are quickly covered or otherwise destroyed and typical values of τ for a basaltic eruption are expected to be on the order of 10 seconds to 10 minutes. Our model suggests that the Galileo SSI eclipse data are consistent with moderately active to quiescent basaltic lava lakes but are not diagnostic of such activity.
Convective thermal evolution of the upper mantles of Earth and Venus
Authors: Nimmo Francis , McKenzie Dan
Published: February 2004

On Earth the present‐day rate of heat loss is about twice the heat generation rate; on Venus it is about half. Though this rough balance may be due to a feedback mechanism between mantle temperature and heat loss, it is difficult to see how such a mechanism can occur on timescales of 1 Ga or less when the upper mantle of the Earth is thought to be cooling at about 40°C Ga−1. On Venus a decrease in surface heat flux presumably occurred at the end of the catastrophic resurfacing event at ∼500 Ma. Parameterized convection models relate heat flux to Rayleigh number by the exponent β. Such models using a range of viscosities and values of β from 0.2 to 0.3 show that the effect of a sudden decrease in surface heat flux is to cause an independently convecting upper mantle to increase in temperature by 100–500°C over 1 Ga, whereas, if whole mantle convection occurs, the temperature change is less than 60°C. An increase in mantle temperature of 200°C or more will affect mantle viscosity, lithospheric thickness and melt generation rate, all of which may affect the feedback mechanism.
Interaction of HNO3 with water‐ice surfaces at temperatures of the free troposphere
Authors: Abbatt Jonathan P. D.
Published: February 2004

The uptake of gas‐phase HNO3 by water‐ice films has been measured in a low‐temperature, coated‐wall flow tube under conditions where water‐ice, and not a hydrate of nitric acid, is thermodynamically stable. It is observed that there is uptake of HNO3 on the order of 1 → 3 ×1014 molecules per cm² of ice film on a short timescale, and a somewhat smaller uptake on a much longer timescale of 10's of minutes. The short timescale uptake is insensitive to the nitric acid partial pressure, varying by not more than a factor of two over a 20‐fold variation in the partial pressure of HNO3 from 1.3 × 10−7 to 3.1 × 10−6 torr. This implies that the ice surface is saturated with HNO3 at these partial pressures. Also, the uptake is somewhat dependent on temperature over the range 208 to 248 K, with the largest uptake at the lowest temperatures. The uptake is largely irreversible, with only 20 → 25% of the adsorbed HNO3 desorbing from the film when the exposure to gas‐phase HNO3 is stopped. These experiments suggest that adsorption to cirrus cloud surfaces may be an important scavenging process of HNO3 in the troposphere.
Concentrations and isotope ratios of dissolved inorganic carbon in denitrifying environments
Authors: Nascimento C. , Atekwana E. A. , Krishnamurthy R. V.
Published: February 2004

We measured the concentration and isotope ratio of dissolved inorganic carbon (DIC) in groundwater associated with denitrification (Corg + NO3−=CO2 + N2) in an agriculturally impacted site in southwestern Michigan. Samples with the lowest nitrate levels also had low dissolved oxygen content and were more depleted in δ13C than background groundwater. All the samples had DIC concentrations in excess of titratable alkalinity. The magnitude of this DIC in excess of alkalinity correlated with a decreasing δ13C attesting to the presence of CO2 derived from organic carbon. Carbon dioxide is one of the by‐products of denitrification. Since the carbon isotope ratio of carbon dioxide produced during denitrification can be expected to be similar to that of the substrate consumed in the process, this can serve as a useful tool in monitoring denitrification. The estimated carbon isotope ratio of source carbon added to the DIC pool via denitrification was close to the value obtained for the organic carbon in the aquifer solids, suggesting that the carbon substrate used in denitrification came from soil organic matter. The results provide support for the hypothesis that the concentration and carbon isotope ratios (δ13C) of dissolved inorganic carbon (DIC) in groundwater might be useful to monitor denitrification.
A model for earthquake generation during unrest episodes at Campi Flegrei and Rabaul Calderas
Authors: Troise Claudia , De Natale Giuseppe , Pingue Folco , Zollo Aldo
Published: February 2004

We have analysed the seismicity that occurred at Campi Flegrei caldera (Italy) in the period 1982–1984, during an unrest episode. Earthquake locations describe a system of inward dipping ring faults. Focal mechanisms of such events show a normal dip component, which is not in agreement with the differential uplift of the inner caldera, as defined by static ground deformations. We have performed a simulation of the stress field generated by overpressure in a magma chamber in presence of lateral discontinuities, using a boundary element method. Lateral discontinuities simulate the ring fault system marking the border of the inner caldera collapse. Results allow us to hypothesize that reverse fault slip on the ring fault is mainly aseismic, and such aseismic movement is able to focus normal fault shear stress along the lateral discontinuities. Aseismic slip on the ring fault in response to static deformation is also supported by the low seismic moment released (M0≅1015 Nm), about two orders of magnitude lower than expected from the shear slip on the discontinuities needed to accomplish the total static surface deformation (1.8 m). Such results have been compared with observations at Rabaul caldera, during a similar unrest episode. In this area, the seismic moment release is in good agreement with shear slip produced on a system of outward dipping ring faults, and seismicity is much more focused on the fault structures. Such a different behaviour can be interpreted, in the framework of our model, as due to the different sign of the stress normal to the ring faults, for inward and outward dip. The comparison between the two areas shed new light about the dynamics of earthquakes in calderas, in terms of the role played by ring fault systems.
Potential use of ERS‐1 and Topex/Poseidon altimeters for resolving oceanographic patterns in the Algerian Basin
Authors: Vignudelli S.
Published: February 2004

Two independent and concurrent (1992–1993) sources of data obtained from ERS‐1 and Topex/Poseidon satellites, provide a first look at the spatial distribution of mesoscale sea surface variability in the Algerian Basin. Values higher than 6 cm rms were found in a narrow band extending along the Algerian slope between 0° and 4°E, where meander formation and eastward eddy propagation occurred. East of 4°E, patterns of higher variability were also seen in the interior of the basin resulting from detachment of eddies from the Algerian Current that drift seaward. Based on geostrophic velocity estimates at crossover points, the eddy field variability appeared to be anisotropic, especially in the vicinity of the Algerian Current. Two mesoscale features whose signatures were clearly identified from altimeter transects, were supported by cloud‐free AVHRR infrared imagery. In particular, the path of an anticyclonic eddy (140 km diameter with drift of ∼3 cm s−1) was sufficiently coherent with the temporal and spatial sampling of altimeters to describe its kinematic behaviour. The results thus demonstrate the potential usefulness of satellite altimetry for monitoring oceanographic conditions in the Algerian Basin.
The normalised optimised anisotropic wavelet coefficient (NOAWC) Method: An Image processing tool for multi‐scale analysis of rock fabric
Authors: Gaillot Philippe , Darrozes José , de Saint Blanquat Michel , Ouillon Guy
Published: February 2004

The 2D Anisotropic Wavelet Transform (2DAWT) is an image analysis tool which is able to decipher signals where information obtained from different scales are intermixed. Extended from the Optimised Anisotropic Wavelet Coefficient method (OAWC) of Ouillon et al. [1995], we present a method which discriminates the objects and groups of objects depending on their area, shape ratio, orientation and position. Illustrated in a synthetic example, we show that this method allows one to distinguish between different sub‐populations of objects within a single phase, and quantify the anisotropies of shape, orientation and spatial distribution at different scales (objects, clusters of objects, alignments of objects or clusters). Applied to a natural rock sample (Sidobre granite, Montagne Noire, France), the 2DAWT has permitted us to detect and accurately characterise the different levels of mineral organisation, and thus, to contribute to the understanding of the physical processes, such as crystallisation, fluid migration, deformation, etc responsible for such organisations.
A magnetotelluric investigation of the San Andreas Fault at Carrizo Plain, California
Authors: Mackie Randall L. , Livelybrooks Dean W. , Madden Theodore R. , Larsen Jimmy C.
Published: February 2004

High quality, wide‐band magnetotelluric data were collected along two profiles crossing the San Andreas fault at Carrizo Plain, California for crustal imaging as part of the San Andreas Deep Drilling Project. Two‐dimensional inversions of the data indicate that the upper crustal part of the San Andreas fault does not appear here as an anomalously conductive zone. Additionally, a broad resistive zone under the Temblor Mountains (east of the fault) suggests resistive crystalline or metamorphic rocks may be present here as opposed to the more conducting Franciscan assemblage, contradicting the generally‐accepted geologic model.
Sprites as evidence of vertical gravity wave structures above mesoscale thunderstorms
Authors: Pasko Victor P. , Inan Umran S. , Bell Timothy F.
Published: February 2004

Large area multicell thunderstorms lead to the formation of vertically oriented cylindrical structures of gravity waves at mesospheric altitudes closely resembling those observed in optical emissions associated with transient luminous glows called sprites.
Jupiter's ionosphere: Results from the First Galileo Radio Occultation Experiment
Authors: Hinson D. P. , Flasar F. M. , Kliore A. J. , Schinder P. J. , Twicken J. D. , Herrera R. G.
Published: February 2004

The Galileo spacecraft passed behind Jupiter on December 8, 1995, allowing the first radio occultation measurements of its ionospheric structure in 16 years. At ingress (24°S, 68°W), the principal peak of electron density is located at an altitude of 900 km above the 1‐bar pressure level, with a peak density of 105 cm−3 and a thickness of ∼200 km. At egress (43°S, 28°W), the main peak is centered near 2000 km altitude, with a peak density of 2×104 cm−3 and a thickness of ∼1000 km. Two thin layers, possibly forced by upwardly propagating gravity waves, appear at lower altitudes in the ingress profile. This is the first in a two‐year series of observations that should help to resolve long‐standing questions about Jupiter's ionosphere.
Dual lidar observations of mesoscale fluctuations of ozone and horizontal winds
Authors: Gibson‐Wilde D. E. , Vincent R. A. , Souprayen C. , Godin S. , Hertzog A. , Eckermann S. D.
Published: February 2004

A case study is presented of 6.5 h of simultaneous colocated stratospheric Differential Absorption Lidar (DIAL) measurements of ozone concentration and Rayleigh‐Mie Doppler (RD) lidar measurements of horizontal wind velocity from the Observatoire de Haute Provence (OHP), France (44°N, 6°E). The RD lidar observations reveal a distinct gravity wave motion at ∼12–18 km, while the DIAL data show laminated ozone structures in the same height range. We combine these data to show that advection due to the gravity wave cannot produce the large ozone lamina at ∼14km.
Spatial variation of accelerated pickup ions at co‐rotating interaction regions
Authors: Giacalone J. , Jokipii J. R.
Published: February 2004

The spatial distribution of accelerated particles at corotating interaction regions (CIR's) provides constraints on possible acceleration mechanisms. We point out some previously unrecognized aspects of acceleration at the forward and reverse shocks bounding CIRs, which support the idea that acceleration of pickup ions at these shocks is an important contributor to energetic ions in the inner heliosphere. We find that the acceleration of pickup ions is strongly favored at the reverse shock over the forward shock. Also, the scaling of the pickup‐ion velocity distribution with respect to local solar wind speed is not necessarily useful within the CIR.
The phase difference between length of day and atmospheric angular momentum at subannual frequencies and the possible role of core‐mantle coupling
Authors: Zatman Stephen , Bloxham Jeremy
Published: February 2004

We examine discrepancies in the angular momentum budget of the Earth on subannual timescales. We find that for signals with long periods (> 30 days) the phase of the length of day (ΔLOD) significantly leads that of the atmospheric angular momentum (AAM). The discrepancy has an amplitude of ≃ 15% of the observed AAM at periods of around 100 days. We show that if changes in the ΔLOD are driven by the atmosphere, then this is diagnostic either of the importance of the oceans or of dynamical coupling between the core and mantle for these frequencies. We find that a simple model of core‐mantle coupling can cause a phase lead of ΔLOD of the correct magnitude. We attempt to fit the transfer function with a simple three‐layer model of the Earth, treating the core as a rotating solid body coupled to the mantle by a specified function. Although our simple model can supply sufficient phase lead of the ΔLOD, the fit to the frequency dependence is poor and it can not fit the magnitude of the transfer function. Nevertheless, this suggests that core‐mantle coupling is a plausible explanation of the observed phase difference. Better fits might be obtained with more realistic models of the core.
The upper mantle beneath the Philippine Sea region from waveform inversions
Authors: Lebedev Sergei , Nolet Guust , van der Hilst R. D.
Published: February 2004

We present a three‐dimensional S‐velocity model for the upper mantle beneath the Philippine Sea region. It was derived from inversions of 281 broad band vertical‐component seismograms recorded in the area at the Global Seismological Network (GSN) and SKIPPY portable array stations. We have been able to obtain high‐resolution tomographic images spanning the depths down to 200–300 km and locally down to the upper transition zone. High‐velocity subducting slabs and low‐velocity volcanic arc regions are the dominant features of the model. Fast, thin lithosphere of back‐arc basins is underlain by a prominent low‐velocity zone. Low velocities at lithospheric depths are observed beneath the extinct Central Basin Ridge in the West Philippine Basin and close to the Eauripik Ridge that separates the East and West Caroline basins. High upper‐mantle heterogeneity and resulting scattering presents a difficulty and limits the resolution, especially below 200–300 km. Explicit modeling of seismic wave diffraction may be necessary for a significant improvement in resolution.
Formation and implications of ice particle nucleation in the stratosphere
Authors: Tabazadeh Azadeh , Toon Owen B. , Jensen Eric J.
Published: February 2004

The classical nucleation theory of homogeneous freezing along with a thermodynamic model of aqueous HNO3 is used to calculate the critical temperatures and compositions at which ice crystals will nucleate from an aqueous HNO3 droplet. Assuming that stratospheric aerosols are composed of aqueous HNO3 near the ice frost point, we show that ice particle formation in the stratosphere can only occur if the air mass is cooled to about 2 to 3 K below the equilibrium condensation point of ice. A simple function is given for predicting the nucleation temperature of ice particle formation in the stratosphere from the ambient water vapor concentration. Microphysical calculations show that only fast cooling rates (> 500 K day−1) encountered in cold lee waves are rapid enough for nucleating the majority of the background aerosols into ice particles. The likelihood that ice crystals formed in lee waves may result in the subsequent crystallization of HNO3 in the droplets is discussed. The barrier to ice formation by heterogeneous gas phase nucleation is compared to that of homogeneous freezing nucleation.
Fast plumeheads: Temperature‐dependent versus non‐Newtonian rheology
Authors: Larsen Tine B. , Yeun David A.
Published: February 2004

In a series of two‐dimensional Cartesian simulations with high resolution, on the order of 2 km, we have compared for the same effective Rayleigh number, around 106, the dynamics between Newtonian and non‐Newtonian rheologies. A viscosity contrast due to temperature of 1200 has been employed throughout with surface dissipation numbers varying between 0.05 and 0.2. Peak velocities for non‐Newtonian plumes are at least 50 times faster than the peak Newtonian velocities and reach magnitudes in excess of m/yr. Upon impinging the surface, plume head structures of the non‐Newtonian rheology contain much greater complexity in the thermal‐mechanical structure than for Newtonian plumes.
Enhanced whistler‐mode emissions: Signatures of interchange motion in the Io torus
Authors: Bolton S. J. , Thorne R. M. , Gurnett D. A. , Kurth W. S. , Williams D. J.
Published: February 2004

During the Galileo inbound pass through the Io torus the plasma wave instrument detected intervals of enhanced whistler‐mode emissions. Over two of these intervals in the inner torus (L < 6.5), for which energetic particle data is also available, the flux and pitch angle anisotropy of resonant electrons exhibited a simultaneous enhancement consistent with inward adiabatic transport from a source region in the outer torus. The enhanced electromagnetic emissions are interpreted as a modulation of cyclotron whistler‐mode instability above the normal marginally stable state of the plasma. This suggests that the enhanced emissions are a sensitive indicator of rapid inward transport associated with interchange motions in the Io torus.
Evidence from driftwood records for century‐to‐millennial scale variations of the high latitude atmospheric circulation during the Holocene
Authors: Tremblay L.‐B. , Mysak L. A. , Dyke A. S.
Published: February 2004

Different Holocene sea‐ice drift patterns in the Arctic Ocean have been hypothesized by Dyke et al. from radiometric analyses of driftwood collected in the Canadian Arctic Archipelago. A dynamic‐thermodynamic sea‐ice model is used to simulate the modes of Arctic Ocean ice circulation for different atmospheric forcings, and hence determine the atmospheric circulations which may have accounted for the inferred ice drift patterns. The model is forced with the monthly mean wind stresses from 1968 (a year with very large ice export) and 1984 (very low ice export), two years with drastically different winter sea level pressure patterns and with different phases of the NAO index. The simulations show that for the 1968 wind stresses, a weak Beaufort Gyre with a broad Transpolar Drift Stream (TDS) shifted to the east are produced, leading to a large ice export from the Arctic. Similarly, the 1984 wind stresses lead to an expanded Beaufort Gyre with a weak TDS shifted to the west and a low ice export. These results correspond to the patterns inferred by Dyke et al. Based on the simulations, the driftwood record suggests that for centuries to millennia during the Holocene, the high latitude average atmospheric circulation may have resembled that of 1968, 1984 and today's climatology, with abrupt changes from one state to the other.
The ionization source near Io from Galileo wake data
Authors: Bagenal Fran
Published: February 2004

From measurements of plasma fluxes obtained along the Galileo trajectory through the wake of Io we estimate the source of ions within 5 RIo of the satellite to be 0.5 to 1.7 × 1028 s−1 (18 to 58% of the canonical 3 × 1028 s−1 torus supply rate). This source of ionization close to Io can supply 0.3 to 0.8 × 1012 watts to the torus plasma (15 to 28% of the canonical 3 × 1012 watts of EUV emissions from the torus). Modeling the energy flux at the spacecraft with local ionization matches the observations reasonably well, which we interpret as evidence against extensive additional charge exchange reactions occurring near Io.
Semi‐Chandler and semiannual oscillations of polar motion
Authors: Kosek W. , Kolaczek B.
Published: February 2004

It has been reported previously that the filtered semiannual oscillation (SAO) of polar motion has a variable amplitude modulated with a period of about 3 years. Assuming, that this quasi 3‐year modulation of the amplitude is caused by the beat of two oscillations, namely the SAO and the semi‐Chandler oscillation (SCHO), we filtered them using the Fourier Transform Band Pass Filter (FT BPF) with carefully choosen parameters. These two oscillations filtered from the astrometric polar motion set of data and the IERS (90C04) combined polar motion data have slightly variable amplitudes modulated with the period of about 11 to 13 years and reaching maxima of about several mas. Similar oscillations were found in the equatorial components of the atmospheric excitation functions computed by the NMC (National Meteorological Center) and JMA (Japan Meteorological Agency). The epochs of the maxima of the time variable coherence between these oscillations of geodetic and atmospheric excitation functions are correlated with El Niño epochs.
Simultaneous observations of the cusp in optical, DMSP and HF radar data
Authors: Yeoman T. K. , Lester M. , Cowley S. W. H. , Milan S. E. , Moen J. , Sandholt P. E.
Published: February 2004

A favourable conjunction of HF coherent radar backscatter, meridian scanning photometer data and an overflight of the DMSP F13 spacecraft has enabled the study of the ionospheric signature of the cusp with these three important techniques simultaneously. Strong HF backscatter power, poleward‐moving red line auroral forms and latitude‐dispersed ion precipitation features are all observed to be collocated. The precipitation of ions in the 0.1–2 keV energy range is found to be very closely associated with the production of the F region irregularities detected by the HF radar.
The fast solar wind
Authors: McKenzie J. F. , Axford W. I. , Banaszkiewicz M.
Published: February 2004

A two‐fluid model for the fast solar wind is described which attempts to account for observations at large distances and close to the Sun in coronal holes, allowing for anisotropic proton temperature, Alfven wave pressure and a realistic magnetic field, but neglecting the effects of proton heat conduction and viscosity. The resulting acceleration of the wind near the Sun is quite rapid, although somewhat less so than in our previous models where the wave pressure was neglected. The proton temperatures in the corona remain relatively high and exceed the associated wave “temperature” out to a heliocentric distance of about 5 solar radii. The proton temperature anisotropy may become very large if the effective particle scattering rate is small and it is suggested that in fact there may be significant particle‐wave scattering in the corona at least.
Topography of the lunar south polar region: Implications for the size and location of permanently shaded areas
Authors: Zuber Maria T. , Smith David E.
Published: February 2004

We analyze Clementine altimetry to constrain the size and location of proposed permanently shadowed regions in the vicinity of the lunar south pole. Long and short wavelength topography in the vicinity of the pole, in combination with measurements of depths of well‐preserved craters and basins and the lunar topographic power spectrum, have direct bearing on the nature of elevations in the south polar region. A criterion based on geometric considerations and altimetry demonstrates that the existence of permanent shadowing is not very sensitive to the elevation of the south pole. In addition, permanent shadowing cannot be a consequence of large structures such as the South Pole‐Aitken Basin and/or a 300‐km degraded polar basin. Perennially dark regions, if they exist, are most likely associated with craters or other axisymmetric features with diameters of at most 80 km centered at the pole. For structures displaced 2° from the pole the maximum allowable diameter decreases to ∼30 km.
Monitoring of global ionospheric irregularities using the Worldwide GPS Network
Authors: Pi X. , Mannucci A. J. , Lindqwister U. J. , Ho C. M.
Published: February 2004

A prototype system has been developed to monitor the instantaneous global distribution of ionospheric irregularities, using the worldwide network of Global Positioning System (GPS) receivers. Case studies in this paper indicate that GPS receiver loss of lock of signal tracking may be associated with strong phase fluctuations. It is shown that a network‐based GPS monitoring system will enable us to study the generation and evolution of ionospheric irregularities continuously around the globe under various solar and geophysical conditions, which is particularly suitable for studies of ionospheric storms, and for space weather research and applications.
Dependence of ozone production on NO and hydrocarbons in the troposphere
Authors: Kleinman Lawrence I. , Daum Peter H. , Lee Jai H. , Lee Yin‐Nan , Nunnermacker Linda J. , Springston Stephen R. , Newman Leonard , Weinstein‐Lloyd Judith , Sillman Sanford
Published: February 2004

An expression for the production rate of O3, P(O3), is derived based on a radical budget equation applicable to low and high NOx conditions. Differentiation of this equation with respect to NO or hydrocarbons (HC) gives an approximate analytic formula in which the relative sensitivity of P(O3) to changes in NO or HC depends only on the fraction of radicals which are removed by reactions with NOx. This formula is tested by comparison with results from a photochemical calculation driven by trace gas observations from the 1995 Southern Oxidants Study (SOS) campaign in Nashville, Tennessee.
Time clustering properties of seismicity in the Etna Region between 1874 and 1913
Authors: De Rubeis Valerio , Tosi Patrizia , Vinciguerra Sergio
Published: February 2004

Time properties of seismic activity of the Etna Volcano (Italy) from 1874 to 1913, are investigated by fractal dimension analysis. Period selection was due to the interesting volcanic and seismic activity which had occurred within this time interval. A catalogue was adopted, revised by the reexamination of historical sources and with the addition of new material. Time evolution of the temporal fractal dimension Dt, calculated on a 40 seismic events moving window, revealed the following correlations with the eruptive processes: long term fractal dimension variations are due to the magma rise from the depth; mid term variations are closely related to stress conditions at the volcano edifice, and short term variations are induced by the onset of eruption. The spatial localisation of data allowed interpretation of seismic activity in relation to the main structural systems outcropping on the volcano edifice and in the surrounding areas.
A twenty‐five year record of stratospheric hydrogen chloride
Authors: Wallace Lloyd , Livingston William , Hall Donald N. B.
Published: February 2004

From 1971 through April 1997 we have tracked the variation of stratospheric HCl using ground‐based spectroscopic observations of the sun. This HCl is a tracer of free chlorine, the agent which catalytically destroys ozone. Our observations are dominated by a general increase in HCl by a factor between three and four, although since about 1990 the rate of increase may have slowed.
Consumption of atmospheric isoprene in soil
Authors: Cleveland Cory C. , Yavitt Joseph B.
Published: February 2004

Natural vegetation annually emits 503 Tg yr−1 of isoprene (2‐methyl‐1,3 butadiene) to the global atmosphere where it reacts very rapidly with hydroxyl radicals and strongly regulates atmospheric chemistry. Current models of the compound's chemical behavior assume the atmosphere is the only significant sink; however, there is evidence that soil may consume isoprene. Here we show through field and laboratory studies that soil exposed to isoprene at low mixing ratios removed isoprene to concentrations below those commonly observed in forest canopies, and that the removal of isoprene was biologically mediated. On the basis of laboratory studies with soil from several different ecosystems worldwide, we provide a first approximation of a global annual soil sink for isoprene of 20.4 Tg yr−1, suggesting a soil sink should be included in models that attempt to describe the effect of isoprene emission on atmospheric chemical processes.
Preliminary results from WOCE hydrographic sections at 80°E and 32°S in the central Indian Ocean
Authors: Talley Lynne D. , Baringer Molly O.
Published: February 2004

The hydrographic properties and circulation along sections at 80°E and 32°S in March, 1995, in the Indian Ocean are described very briefly. A halocline was well‐developed in the tropics. A westward coastal jet of fresh Bay of Bengal water was present at the sea surface at Sri Lanka with eastward flow of saline Arabian Sea water below. The Equatorial Undercurrent was well developed as were the deep equatorial jets. The Indonesian throughflow jet presented a large dynamic signature at 10 to 14°S coinciding with a strong front in all properties to great depth. Its mid‐depth salinity minimum is separated from that of the Antarctic Intermediate Water. The Subantarctic Mode Water of the southeastern Indian Ocean imparts its high oxygen ventilation signature to the whole of the transects, including the tropical portion. The deepest water in the Central Indian Basin is pooled in the center of the basin, and its principal source appears to be the sill at 11°S through the Ninetyeast Ridge. Northward deep water transports across the 32°S section were similar to those observed in 1987 but the deep water was lower in oxygen and fresher than in 1987. Upper ocean waters at 32°S were more saline and warmer in 1995.