bluuebunny/crossref_metadata_2025 huggingface dataset:
Geochemistry of carbon dioxide in seawater at the Hawaii Ocean Time Series Station, ALOHA
Authors: Sabine Christopher L. , Mackenzie Fred T. , Winn Christopher , Karl David M.
Published: February 2004

This paper examines the fundamental biological and physical processes controlling the distribution of the inorganic carbon species throughout the water column at the Hawaii Ocean Time series station, ALOHA. Profiles of alkalinity and calcium are strongly influenced by the distribution and movement of the six water masses at this location. The semiconservative behavior of these parameters can be useful in identifying water masses. The dissolution of carbonate particles, however, contributes up to 21% (49 μmol C kg−1) of the dissolved inorganic carbon added to the intermediate waters between the time the waters enter the Pacific and the time they reach Station ALOHA. A sharp increase in carbonate‐derived carbon observed between 800 and 2200 m is due to the dissolution of the more soluble forms of carbonate such as aragonite. The distribution of TCO2 and pH at this site are significantly affected by biological processes as indicated by the apparent nonlinear mixing curves between water masses, the similarity of the measured ratios of C:N and C:P to the Redfield ratios in the upper 700 m of the water column, and the results of a carbon system model. The nonconservative nature of these properties demonstrates that both physical and biological factors must be considered when evaluating temporal variability. The carbon system evaluation techniques presented here are similar to those used on several previous trans‐Pacific cruises allowing the results from this station to be compared to the results of other cruises in this area.
Measurements of stable isotope ratios(13CH4/12CH4; 12CH3D/12CH4) in landfill methane using a Tunable Diode Laser Absorption Spectrometer
Authors: Bergmaschi Peter , Harris Geoffrey W.
Published: February 2004

Variations in the isotopic composition (δ13C, δD) of methane produced within a landfill site near Mainz, Germany, were studied using a newly developed tunable diode laser absorption spectrometer (TDLAS) method. Additional data on the mixing ratios of CO2, O2, N2, CH4 itself and δ13C of the CO2 in the landfill gas were also acquired. Samples taken from several branches of the landfill biogas collection system had methane isotopic compositions in the range δ13C = −62.3 to −55.3‰ VPDB (n = 23) and δD = −327 to −287‰ VSMOW (n = 23). Although the variability of the stable isotope ratios is small, several significant correlations were found between these and the other measured parameters, which provide insight into the microbiological processes occurring within the landfill. Several samples showed evidence of admixture of atmospheric air which occurs when the pumping rate in the collection branch exceeds the local methane production rate. A fraction of the atmospheric oxygen is consumed during the passage through the landfill and CO2 is produced in addition to the CO2 associated with methanogenesis. The consumption of oxygen is correlated with the δ13C and δD of CH4 and the δ13C of CO2. The correlation is consistent with partial bacterial oxidation of CH4 resulting in the progressive enrichment of the remaining CH4 (α(δ13C) = 1.008 ± 0.003 and α(δD) = 1.044 ± 0.020) and in the formation of very depleted CO2. For samples showing no evidence of oxidation, there was a negative correlation between δD and δ13C(CH4)(r = −0.86, n = 14) and between δ13C(CO2) and δ13C(CH4) (r = −0.95, n = 14), which we interpret as originating from slightly varying contributions from the two methanogenic pathways CO2 reduction and acetate fermentation.
Modeling isotopic fractionation in systems with multiple sources and sinks with application to atmospheric CH4
Authors: Andersen B. L.
Published: February 2004

A formula for calculation of the isotopic composition parameter δ in a system with any number of sources and sinks is derived. It is applied to the isotope pairs 13C/12C and to 2H/H in atmospheric methane for which the importance of isotope fractionation in the sink processes is illustrated.
Ground‐based remote sensing of the decay of the Pinatubo eruption cloud at three northern hemisphere sites
Authors: Jäger H. , Uchino O. , Nagai T. , Fujimoto T. , Freudenthaler V. , Homburg F.
Published: February 2004

Three lidar systems at the northern hemisphere sites of Naha and Tsukuba, both in Japan, and Garmisch‐Partenkirchen, Germany, have been observing the evolution, spread and decay of the aerosol cloud which had formed in the stratosphere after the explosive eruption of the Philippine volcano Pinatubo in mid‐June 1991. Three years of lidar measurements show the depletion of the initial equatorial aerosol reservoir and the subsequent transport to the north. These lidar data are the basis for the calculation of the climatically relevant parameters aerosol optical depth, mass and surface area.
Plate boundary segmentation by stress directions: Southern San Andreas Fault, California
Authors: Wyss Max , Lu Zhong
Published: February 2004

We propose a new method for defining segmentation of plate boundaries and faults, based on the directions of the stress tensor. Estimates for these directions are obtained by minimizing the average misfit between the theoretical and observed slip directions on fault planes of earthquake focal mechanisms. The misfit, f, for an individual earthquake is the parameter we use for defining the segmentation of plate boundaries. We hypothesize that the stress directions along plate boundaries, and faults, are uniform within segments, but different from other segments. If this is true, a cumulative plot of f as a function of space along strike will show constant, but different, slopes for each segment. The significance of the difference between segment‐slopes can be estimated by the standard deviate z‐test. Applying this method to the San Andreas fault from the Carrizo plains to its southern end, we identify quantitatively the same four boundaries between segments as proposed based on non‐quantitative tectonic considerations, plus one additional segment boundary. We interpret the relatively uniform, but segmented, distribution of stress directions as due to the changing strike, and possibly changing fault surface properties. Whether great earthquake ruptures, or their major asperities, may terminate at segment‐boundaries, should be determined along faults that recently generated large earthquakes. This method of defining fault segmentation also allows identification of volumes with uniform stress directions, suitable for inversion for stress orientations, with a minimum of computing time. And finally the method affords an alternative estimate of the significance of differences in stress directions.
Two‐dimensional structure of slow shocks
Authors: Omidi N. , Johnson M. , Krauss‐Varban D. , Karimabadi H.
Published: February 2004

The two‐dimensional (2‐D) structure of switch‐off slow magnetosonic shocks is investigated using an electromagnetic hybrid (fluid electrons, kinetic ions) code. It is shown that the basic physical processes occurring at 1‐D slow shocks are also operative in 2‐D. Specifically, the interaction between the upstream ions and those streaming away from the shock results in the excitation of Alfvén/ion‐cyclotron (AIC) waves. Depending on the plasma parameters, these waves may either stay in the upstream or convect back into the shock resulting in a non‐steady shock behavior which prevents the formation of a trailing wave train. Despite this similarity, some slow shocks which are steady in 1‐D are found to be non‐steady in 2‐D. Fourier analysis of the waves downstream of non‐steady shocks identifies them as AIC, demonstrating that the waves remain on the same branch as they convect from upstream into the downstream region.
Quantum yield for carbon monoxide production in the 248 nm photodissociation of carbonyl sulfide (OCS)
Authors: Zhao Z. , Stickel R. E. , Wine P. H.
Published: February 2004

Tunable diode laser absorption spectroscopy has been coupled with excimer laser flash photolysis to measure the quantum yield for CO production from 248 nm photo‐dissociation of carbonyl sulfide (OCS) relative to the well‐known quantum yield for CO production from 248 nm photolysis of phosgene (Cl2CO). The temporal resolution of the experiments was sufficient to distinguish CO formed directly by photodissociation from that formed by subsequent S(³PJ) reaction with OCS. Under the experimental conditions employed, CO formation via the fast S(¹D2) + OCS reaction was minimal. Measurements at 297K and total pressures from 4 to 100 Torr N2 + N2O show the CO yield to be greater than 0.95 and most likely unity. This result suggests that the contribution of OCS as a precursor to the lower stratospheric sulfate aerosol layer is somewhat larger than previously thought.
Traversal of comet SL‐9 through the Jovian magnetosphere and impact with Jupiter: radio upper limits
Authors: Desch M. D. , Kaiser M. L. , Farrell W. M. , MacDowall R. J. , Stone R. G.
Published: February 2004

Continuous radio observations below 1 MHz of Jupiter from the Ulysses spacecraft are used to establish an upper limit to the radiated power at low frequencies associated with the traversal through the magnetosphere and impact of Comet SL‐9 with the planet. Although Jovian emissions were observed throughout the impact interval, no systematic intensity changes were observed before, during, or after the fragment impact times as a whole. Examined individually, a large intensity increase, probably associated with a solar wind compression at Jupiter, was observed at the time of the P impact. Intense solar type III bursts, which can sometimes be confused with Jovian emissions, occurred often, which serves as a caution to other (groundbased) radio observers. We derive an upper limit for the interfragment dust density of 10−3/m3 in the context of a dust‐magnetosphere interaction model proposed earlier.
In situ measurements of BrO During AASE II
Authors: Avallone L. M. , Toohey D. W. , Schauffler S. M. , Pollock W. H. , Heidt L. E. , Atlas E. L. , Chan K. R.
Published: February 2004

BrO measured from the NASA ER‐2 during AASE II exhibited a mean value (for 20‐minute averages) of 5.4±0.3 pptv, with a standard deviation of 3.1 pptv. Ratios of BrO to available inorganic bromine (Bry) show only slight increases in polar regions relative to midlatitudes. A comparison between observed latitudinal and diurnal variations of this same ratio and that calculated by photochemical models shows reasonable agreement in behavior, but significant discrepancies in magnitude. It is unclear whether this difference is due to errors in measurements, models or both.
An automatic seismic event processing for detection and location: The P.M.C.C. Method
Authors: Cansi Y.
Published: February 2004

We present a new method for automatic detection and location of seismic events recorded on a network. It is based on a progressive study of the interstation correlation functions, which leads to a consistent set of time‐delays when a seismic phase is present. Three different examples are processed on networks of different sizes.
Polar stratospheric clouds as deduced from MLS and CLAES measurements
Authors: Ricaud P. D. , Carr E. S. , Harwood R. S. , Lahoz W. A. , Froidevaux L. , Read W. G. , Waters J. W. , Mergenthaler J. L. , Kumer J. B. , Roche A. E. , Peckham G. E.
Published: February 2004

From 30 August 1992 to 3 September 1992 a supersaturated area at 465 K potential temperature (∼50 hPa) is deduced from MLS water vapour measurements over western Antarctica, where high extinction coefficients measured by CLAES indicate Polar Stratospheric Clouds (PSCs). These PSCs are attributed partly to the effect of an anticyclone located over South America and partly to localized orographic waves, which raise the isentropes and generate rapid adiabatic cooling. A local minimum in column O3 (≤ 200 DU) is observed in this area, which is believed to be a consequence of the dynamics. Enhanced ClO abundances downstream of the region indicate PSC processing and chlorine activation.
SKS splitting beneath southern California
Authors: Liu H. , Davis P. M. , Gao S.
Published: February 2004

Measurements of SKS phase splitting were obtained from nineteen seismic stations in southern California. The fast polarization directions are 53° at the southern end of the Great Valley, 82±8° in the western Transverse Ranges and northern Peninsular Ranges, 95±4° in Mojave Desert, and 70° on San Clemente Island. The splitting time ranges from 0.8 to 1.8 seconds, which is consistent with an anisotropic layer of 100 to 200 km thick for 4% anisotropy.
Infrared band intensities and global warming potentials of CF4, C2F6, C3F8, C4F10, C5F12, and C6F14
Authors: Roehl C. M. , Boglu D. , Brühl C. , Moortgat G. K.
Published: February 2004

IR band intensities have been measured for the species: CF4, C2F6, C3F8, C4F10, C5F12, and C6F14 via Fourier transform spectroscopy and compared to previous literature values if available. Relative radiative forcing calculations have been performed using these data in order to determine the global warming potential of the particular species. The relative forcing (compared to CFC11, per volume) increases with molecular weight in the above series from 0.47 to 2.1, the GWP for a time horizon of 100 yrs from 1.1 to 4.7. This corresponds to a GWP on CO2 basis per mass of about 5000.
Broadband analysis of the 21 September, 1993 Klamath Falls Earthquake Sequence
Authors: Dreger Douglas , Ritsema Jeroen , Pasyanos Michael
Published: February 2004

The source characteristics of the Klamath Falls earthquake sequence were estimated from broadband seismograms recorded by the Berkeley Digital Seismic Network (BDSN), TERRAscope, and western United States IRIS stations. Solutions were obtained for events ranging in size from Mw 3.8 to Mw 6.0. An empirical Green's function inverse approach was used to estimate kinematic source parameters of the two Mw 6.0 mainshocks. Both events were found to have ruptured northwest on adjacent segments of the Lake of the Woods system of normal faults. The two main‐shocks abut where there is a pronounced 10° to 20° clockwise rotation of strike which may have initially acted as a barrier to a through‐going Mw 6.2 event.
Can gamma radiation be produced in the electrical environment above thunderstorms?
Authors: Chang Britton , Price Colin
Published: February 2004

Our calculations indicate that regions above large mesoscale convective systems may be favorable electrical environments for the production of gamma radiation by runaway electrons in bremsstrahlung collisions. It is well known [Gurevich, 1961] that an electric field however small can accelerate an electron continuously until the electron leaves the region of the electric field, as long as the electric field is larger than the opposing force of friction. Since the force of friction is proportional to the density of air, the resistance on an electron decreases with altitude. The resistance can be expressed in terms of a critical field, which is the strength the field needs to exceed in order to initiate the runaway phenomena. The critical field characterizing the friction is between 7×10−15 and 15×10−15 V‐cm² times the number density of air. Thus a reasonable electric field (500 V/m) at high altitudes results in a force that can be larger than the force of friction. The rate for producing high energy electrons by the electric fields over large thunderstorms is estimated from Gurevich's model of runaway electrons in a weakly ionized plasma. It is found that the number of gamma photons produced by the runaway electrons in the discharge volume is consistent with the data recently observed by satellite [Fishman et al., 1994].
Electron‐impact ionization of interstellar hydrogen and helium at interplanetary shocks
Authors: Isenberg Philip A. , Feldman William C.
Published: February 2004

We investigate the ionization of interstellar hydrogen and helium due to electron impact by shock‐heated electrons. Taking the electron distributions measured at four interplanetary shocks at 1 AU, we show that the electrons in the downstream region of strong shocks can ionize interstellar atoms at rates matching or exceeding the nominal photoionization or charge‐exchange rates. We suggest that this process may explain some puzzling observations of interstellar pickup ions made by the Ulysses spacecraft.
Raman spectroscopic study on the nitrogen/oxygen ratio in natural ice clathrates in the GRIP Ice Core
Authors: Pauer Frank , Kipfstuhl Josef , Kuhs Werner F.
Published: February 2004

We have carried out Raman spectroscopic experiments on air clathrates in the GReenland Ice Core Project (GRIP) deep ice core. We present new N2/O2 measurements that markedly differ from previous measurements of the Dye‐3 ice core: the N2/O2 ratio we observe is much closer to atmospheric. This has new implications for the interpretation of gas distributions in ice sheets and the reconstruction of past atmospheric conditions.
Mid‐UV acetylene cross‐sections revisited: Sample contamination risk in source data
Authors: Bénilan Yves , Andrieux Dominique , Bruston Paul
Published: February 2004

We have reviewed the most recent results on acetylene absorption in the weak A‐X band system (features longward of 185 nm). Then, using acetone absorption measurements in the 185–200 nm range together with saturated vapor pressure studies of acetone, we are able to resolve discrepancies noted by several authors for some A‐X bands.
The effect of introducing continuity conditions in the constrained sinusoidal crossover adjustment method to reduce satellite orbit errors
Authors: Hsu Shu‐Kun , Géli Louis , Guénal Davalan
Published: February 2004

The constrained sinusoidal crossover adjustment method [Tai, 1988] is one of the most efficient and frequently used method to remove the orbit error in satellite altimetry. In this method, the orbit error for each different satellite revolution is represented by a different sine wave, with wavelength equal to the circumference of the earth. One drawback of this method is that the orbit error function is theoretically not forced to be continuous between every two successive revolutions. In this short note, we study the effect of introducing rigorous continuity conditions between every two successive revolutions, and constraints to avoid an offset from a probable variation datum level. To achieve the continuity, the orbit error for each revolution is modelled as a temporal function composed of a sinusoidal function and a second‐order polynomial. Examples using ERS‐1 data show that for local studies, when one demands the geoid height in the neighbourhood of the junction between every two successive cycles, it is recommended to fulfill the continuity conditions. Otherwise, the simple constrained sinusoidal crossover adjustment method must be preferred.
Effect of absorbing aerosols on global radiation budget
Authors: Chylek Petr , Wong J.
Published: February 2004

An expression for a globally averaged value of direct radiative forcing by absorbing aerosols is derived and applied to the case of smokes produced by biomass burning. It is shown that the direct radiative forcing due to the biomass burning aerosols is a sensitive function of the size distribution of aerosol particles. For the range of measured size distributions of smoke aerosols the direct radiative forcing varies between −0.2 and −1.1W/m².
Nitric acid adsorption on ice: A preliminary study
Authors: Laird S. K. , Sommerfeld R. A.
Published: February 2004

The adsorption of nitric acid vapor on the ice surface was studied at −20°C. Adsorption took place in three stages: surface initialization, formation of a monolayer and formation of a multilayer. The results of elution of a multilayer deposit indicated the formation of a hydrate whose vapor pressure was estimated to be a maximum of 1.5 ± 0.5 ×10−6 torr.
A controlled in‐situ investigation of the relationship between stress, velocity and induced seismicity
Authors: Maxwell S. C. , Young R. P.
Published: February 2004

A p‐wave velocity survey was performed after the excavation of a cylindrical, horizontal tunnel through homogenous, visibly unfractured granite. An image of the velocity structure around the tunnel indicated a distinct zone of high velocity corresponding to a zone of increased elastic stresses, where a break‐out notch formed. Perpendicular to this zone, a region of decreased velocity was found associated with a region of tensile elastic stress. The stress changes are believed to have preferentially opened and closed pre‐existing micro‐fractures in the rock, thereby decreasing and increasing the p‐wave velocity. Additional velocity decreases are also attributed to creation of new fractures. The excavation‐induced microseismicity is found to be generally associated with the high‐velocity region adjacent to the notch, and appears to be located along the boundary between the fractured, low‐velocity and high‐velocity regions.
Vertical transport by convective clouds: Comparisons of three modeling approaches
Authors: Pickering Kenneth E. , Thompson Anne M. , Tao Wei‐Kuo , Rood Richard B. , McNamara Donna P. , Molod Andrea M.
Published: February 2004

We have performed a preliminary comparison of the GEOS‐1 (Goddard Earth Observing System) data assimilation system convective cloud mass fluxes with fluxes from a cloud‐resolving model (the Goddard Cumulus Ensemble Model, GCE). A squall line case study (10–11 June 1985 Oklahoma PRESTORM episode) is the basis of the comparison. Regional (central U. S.) monthly total convective mass flux for June 1985 from GEOS‐1 compares favorably with estimates from a statistical/dynamical approach using GCE simulations and satellite‐derived cloud observations. The GEOS‐1 convective mass fluxes produce reasonable estimates of monthly‐averaged regional convective venting of CO from the boundary layer at least in an urban‐influenced continental region, suggesting that they can be used in tracer transport simulations.
Slow wave imaging of permeable rocks
Authors: Nagy Peter B. , Bonner Brian P. , Adler Laszlo
Published: February 2004

A high‐resolution slow wave imaging system based on attenuation measurement of transmitted airborne ultrasonic waves was developed to study the inhomogeneous pore structure in permeable formations. Currently, the threshold sensitivity of our system is approximately 100 mD, making possible the characterization of typical petroleum reservoir rocks with spatial resolution of between 0.5 and 5 mm in the 50 kHz to 500 kHz frequency range. The degree of disorder in permeable solids is of crucial importance especially when the relative permeability is considered. It is expected that this new technique can complement such methods as hydrodynamic dispersion measurements and petrography for characterizing flow in porous rocks.
Large‐scale spatial patterns in topography at Alpha Regio, Venus
Authors: Finn V. Sumin , Baker V. R. , Dolginov A. Z. , Gabitov I. , Dyachenko A.
Published: February 2004

Hypsometric topographic analysis of Magellan altimetry data at Alpha Regio results in a multimodal distribution. Planimetric display of the spatial distribution for altitudes close to each mode reveals large‐scale ring‐like and crescentic patterns. The latter result from the intersection of horizontal altitude ranges with sloping patterns that are quasi‐circular in shape. The spatial patterns of topographic features near Alpha Regio have the following attributes: (1) quasi‐circular shapes of individual elements; (2) a hierarchy of distinctive sizes for those elements, with diameters of various elements at approximately 2800, 1500, 500–700, and 200 km; and (3) a large‐scale arrangement or pattern in which the 1500‐km highland plateau of Alpha Regio is surrounded by a ring of 500‐km structures, all of which constitute a 2800‐km megastructure. We hypothesize that the intricate patterns of hierarchical scaling for large‐scale spatial elements of Venusian topography result from corresponding complexity in Venusian mantle convection.
FTIR studies of low temperature sulfuric acid aerosols
Authors: Anthony S. E. , Tisdale R. T. , Disselkamp R. S. , Tolbert M. A. , Wilson J. C.
Published: February 2004

Fourier transform infrared (FTIR) spectroscopy was used to study low temperature sulfuric acid aerosols representative of global stratospheric sulfate aerosols (SSAs). Sub‐micrometer sized sulfuric acid (H2SO4) particles were generated using a constant output atomizer source. The particles were then exposed to water vapor before being injected into a low temperature cell. Multipass transmission FTIR spectroscopy was used to determine the phase and composition of the aerosols as a function of time for periods of up to 5 hours. Binary H2SO4/H2O aerosols with compositions from 35 to 95 wt % H2SO4 remained liquid for over 3 hours at temperatures ranging from 189–240 K. These results suggest that it is very difficult to freeze SSAs via homogeneous nucleation. Attempts to form aerosols more dilute than 35 wt % H2SO4 resulted in ice formation.
A climatological study of tropical thunderstorm clouds and lightning frequencies on the French Guyana Coast
Authors: Molinié J. , Pontikis C. A.
Published: February 2004

The climatological conditions that are favorable to thunderstorm cloud development in the coastal zone of French Guyana are investigated. The analysis reveals that both the thunderstorm occurrence and the mean monthly lightning frequency are correlated to the Intertropical Convergence Zone annual oscillation, thus increasing from March to August when the South‐East trade‐wind flux drives continental air masses towards French Guyana and decreasing from September to February when French Guyana is under the influence of maritime air masses driven by the North‐East trade‐wind. The study of the lightning frequency values, observed during individual thunderstorm events, as a function of the cloud‐top height shows that these values are intermediate to the lightning frequency values deduced from the parameterizations proposed by Price and Rind (1992) for typical continental and maritime thunderstorm clouds of a similar height. This behavior suggests that the air masses in which thunderstorm clouds develop in the French Guyana coast are mixed air masses with intermediate characteristics. Further, the absence of correlation between the lightning frequency values and both the cloud‐top heights and the corresponding convective available potential energy (CAPE) values indicates that these parameters can not be used to predict lightning activity in these clouds. Most probably, the aerosol concentrations in the subcloud layer and consequently the cloud droplet concentrations play an important role in the development of lightning activity in the considered clouds.
Observations of ultraviolet light reflection and transmission by first‐year sea ice
Authors: Perovich Donald K.
Published: February 2004

As part of a comprehensive program investigating the electromagnetic properties of sea ice, measurements were made of the optical properties of young ice and first‐year sea ice at ultraviolet wavelengths. Young sea ice observations were made in a specially designed sea ice pond at the Cold Regions Research and Engineering Laboratory (Hanover, NH), while first‐year sea ice was examined in the Chukchi Sea and Beaufort Sea near Barrow, Alaska. The results indicated that, in general, albedo increased with increasing wavelength from 305 to 380 nm, with values for first‐year ice in the 0.4 to 0.6 range. Transmittance through bare first‐year ice was roughly 0.5 to 2 percent. Extinction coefficients for bare sea ice were between 2 and 4 m−1 and decreased with increasing wavelength. The presence of a snow cover had a profound impact on ultraviolet light levels under sea ice, with even a thin (0.1‐m‐thick) snow cover reducing transmitted ultraviolet light by more than an order of magnitude. Observed transmittances indicated that the attenuation of ultraviolet light by sea ice and snow was greater than that of the photosynthetically active radiation.
Satellite radar interferometric map of the coseismic deformation field of the M = 6.1 Eureka Valley, California Earthquake of May 17, 1993
Authors: Massonnet Didier , Feigl Kurt L.
Published: February 2004

Interferometric combination of pairs of synthetic aperture radar (SAR) images acquired by the ERS‐1 satellite before and after the Eureka Valley, California earthquake of May 17, 1993 maps the coseismic deformation field. The fringes corresponding to contours of equal change in satellite‐to‐ground distance can be enhanced by forming the sum of two of such interferograms with altitudes of ambiguity roughly equal in magnitude but opposite in sign. The resulting composite interferogram reveals some 10 cm of change in range indicating a coseismic deepening of the Eureka Valley graben. After unwrapping, filtering and decimation, the range changes are used to estimate the centroid and focal mechanism. These estimates indicate normal faulting on a rupture patch compatible with the distribution of aftershocks and mapped Quaternary faults. The change in elevation produced by this earthquake resembles the current topography scaled by a factor of 20,000.
Directivity analysis of the Deep Bolivian Earthquake of June 9, 1994
Authors: Beck Susan L. , Silver Paul , Wallace Terry C. , James David
Published: February 2004

The June 9, 1994 deep Bolivian earthquake (MW = 8.3, d = 636 km) occurred on a nearly horizontal rupture plane with an approximate area of 2000 km². The rupture plane is constrained by directivity analysis of the P wave displacement pulses recorded at local, regional, and teleseismic distances. The fact that there are local recordings of the displacement provides a strong constraint on the vertical extent of faulting, which is less than ∼10 km. The moment release had at least four distinct episodes, or subevents. The best overall explanation for the subevents is rupture which initiates on the western margin of the fault plane, propagates to the east, and then continues bilaterally along a 350° azimuth, with most of the moment release occurring to the north. The apparent rupture velocity between subevents is very low, approximately 1–2 km/s.
Consideration of the Martian magnetotail as evidence for an intrinsic magnetic field
Authors: Brecht Stephen H.
Published: February 2004

It has been suggested by Verigin et al. [1993] that the response of the Martian magnetotail to changes in the solar wind ram pressure indicates the presence of an intrinsic dipole magnetic field. 3‐D hybrid particle simulations of Mars were performed including the magnetotail regions. The simulations are in agreement with published Phobos 2 data from the 3 elliptical orbits and reproduce the magnetopause diameter dependence on the solar wind ram pressure reported by Verigin et al. [1993]. However, the simulations were performed with no intrinsic field present, indicating that the dependence of the magnetotail width on ram pressure, is not a discriminator for the presence of the intrinsic field.
Oceanic topography and heatflow: Indications for a silent discharge of cold rock into the convecting Earth
Authors: Agnon Amotz , Lyakhovsky Vladimir
Published: February 2004

The 2.5 km mean relative elevation of mid ocean ridges is arguably consistent with a steady state thickness of ≈100 km for the oceanic lithosphere. Here we explore some consequences of this particular value. Based on seismic models of the uppermost oceanic mantle, we infer that no significant heat is added to normal asthenosphere following accretion at spreading centers. Therefore we adopt the view that kinematic thinning moderates the conductive thickening to yield the steady state thickness of ≈100 km. We devise a method for estimating mean rates of thinning directly from topography‐age data, with no assumptions on the detailed dynamics of delamination. We find that delamination delivers a significant fraction (>20%) of the global downwelling discharge. This large non subducting discharge of cold lithospheric material provides an explanation for the most robust features of upper‐mantle tomography, and should be considered in studies of mantle cooling and mixing.
A search for variations in the light curves of Io and Europa during the impact of comet SL9: A, H, and Q Events
Authors: Consolmagno Guy J. , Menard Gary
Published: February 2004

We observed Europa (A event) and Io (H and Q events) with a high speed photometer at the 0.6m telescope at Castel Gandolfo, Italy, to search for impact light echoes. Although several fluctuations in light level from these moons were detected, most can be attributed to terrestrial effects. However, some signals during all three events cannot be easily diagnosed as spurious, and may represent real flashes. In particular, we see possible light echoes (at roughly the 2‐sigma level) for the A, Q2 and Q1 events; an increase in signal from Io during the brightest part of the H event as seen from Earth; and a three‐sigma event four minutes after the Q2 event that matches a similar event observed in Kiev.
Earthquakes in a model of seismic zone with embedded pre‐existing faults
Authors: Bhagavatula Ravi , Chen Kan , Jayaprakash C.
Published: February 2004

We construct a simple quasi‐static model of seismic zone with embedded pre‐existing faults and present a self‐consistent method for incorporating both the stick‐slip behavior at the fault surfaces and the long‐ranged stress redistribution following a rupture or a slip event. Driven by a slow tectonic plate (relative) motion, the model evolves to a critical state exhibiting Gutenberg‐Richter power law for the frequency‐size distributions. Results on spatial and statistical features of earthquakes in the model are also presented.
Recent variations in mean temperature and the diurnal temperature range in the Antarctic
Authors: Jones P. D.
Published: February 2004

Monthly mean surface temperature data are available from nearly twenty stations for the period since the International Geophysical Year 1957. All but three stations show an increase in mean temperatures over this time, amounting in the average to 0.57°C over 1957 to 1994. All of this warming occurred before the early 1970s. Since then, there has been no change. The warming has been greatest in the Antarctic Peninsula. Analyses of the less‐widely available diurnal temperature range (DTR) (maximum‐minimum) data show regions of increase and decrease over Antarctica. An average continental DTR series shows no trend over 1957 to 1992. Analyses for six mid‐to‐high latitude Southern Ocean islands show increases in mean temperature over 1961–90. Given the low year‐to‐year variability in these data, these trends are more significant than for any of the stations on the Antarctic continent. The marked decrease in mean temperatures over Antarctica during 1993 and 1994 seems unrelated to sea‐ice variations which show little change since the early 1980s.
Characterization of ozone plumes in eastern Germany
Authors: Klemm O. , Werhahn J. , Schaller E. , Schlager H. , Krautstrunk M.
Published: February 2004

During a photosmog period in summer 1993, several ozone plumes (enrichment of O3 of 10–45 ppb over levels of surrounding air masses) were observed in the southern part of eastern Germany. Analyses of the plumes for other species reveal that SO2, NOy, CO, and photochemically formed CH2O were enriched synchronously with O3. The measured enhancement factors SO2/CO and NOy/CO agree well with emission factors of local emission inquiries. The O3 production potential in the plumes must have originated from emissions from furnaces burning sulfur rich lignite coal under non‐optimum conditions such as old power plants, industrial plants, and domestic water heating systems. The co‐emission of VOC's with SO2 lead to the formation of O3 and CH2O. Most of the plumes seem to be less than one day old.
Seismic anisotropy in the D″ layer
Authors: Vinnik Lev , Romanowicz Barbara , Le Stunff Yves , Makeyeva Larissa
Published: February 2004

We present observations of diffracted SV (SVd) for a path between the Fiji‐Tonga islands and the eastern coast of North America at distances greater than 110°. Observed features of S diffracted suggest that coupling between SVd and SHd can be ruled out as a first order effect for this path. Arrivals of SHd are late relative to IASP91 travel‐times by about 10 s, and those of SVd are late relative to SHd by 3 s, for most records. The slope of the log(SVd/SHd) spectral ratio is around 3Hz−1 in the range 0.06–0.15 Hz. A transversely isotropic low‐velocity layer in the lower‐most mantle with a thickness of 200–300 km may account for most of the observed properties of SVd.
Assessment of the SAGE sampling strategy in the derivation of tropospheric water vapor Distribution in a general circulation model
Authors: Zhang M. H.
Published: February 2004

The Stratospheric Aerosol and Gas Experiment (SAGE) II has provided unprecedented information of water vapor distribution in the upper troposphere. For the purpose of comparison with output from climate models, the present study assesses the impact of the SAGE II sampling strategy on the tropospheric water vapor climatology in a general circulation model. Since water vapor is sampled only in “non‐cloudy” regions in the SAGE strategy, the sampled water vapor concentration is smaller than the real climatology. This difference is associated with two factors. One is the water‐vapor sampling frequency, the other is the humidity variability inside and outside the clouds. It is shown that maximum difference is at around 300 to 500 mb where it reaches up to 40% in the zonal mean humidity.
Hydromagnetic discontinuities from the evolution of nonlinear Alvén waves
Authors: Lee Nam C. , Parks George K.
Published: February 2004

To study the large‐amplitude Alfvén waves that are frequently observed in the solar wind, the nonlinear equations of electron and ion fluids coupled to Maxwell equations have been solved to obtain the relationships between the fluid density and magnetic field for finite amplitude Alfvén waves in the cold plasma limit. Two regimes of the parameter ωc/Ω (ratio of characteristic frequency to the ion Larmor frequency) are examined. When ωc/Ω = 0, we obtain an exact simple wave solution for the linearly polarized Alfvén wave, and recover the earlier results of [Montgomery, 1959a]. For finite ωc/Ω geometric optics approximation which is valid for large wave numbers yields a new relationship which involves elliptically polarized Alfvén waves. Both of these waves can be shown to evolve into shocks.
Evidence for a solar wind slowdown in the outer heliosphere?
Authors: Richardson J. D. , Paularena K. I. , Lazarus A. J. , Belcher J. W.
Published: February 2004

Voyager 2 and IMP 8 plasma data are used to look for the predicted slowdown of the solar wind with heliospheric distance. Decreases of roughly 7% in the radial velocity and of the same order in the flux are found if the Voyager 2 and IMP 8 velocities are normalized to agree in the inner heliosphere. This decrease is consistent with a pickup ion density equal to 8% of the total ion density, similar to predictions and other determinations of this density. Comparison with published model results allows us to infer an interstellar neutral density of 0.05 cm−3.
Source time function of the Great 1994 Bolivia Deep Earthquake by waveform and spectral inversions
Authors: Ihmlé Pierre F. , Jordan Thomas H.
Published: February 2004

The source time function of the great 1994 Bolivia deep earthquake is estimated from far‐field seismograms by two techniques: time‐domain inversion of direct P and S waveforms, and spectral‐domain inversion of a combination of body waves, first‐orbit traveling modes, and free oscillations. Both methods give consistent estimates, but the latter provides more bandwidth (1–300 mHz) and is more robust with respect to source‐directivity effects and wave scattering. The earthquake released a total moment of 2.7 (±0.1) × 1021 Nm over an interval of about 50 s. Its history is highly episodic and can be divided into three stages: an initial sequence (0 ≲ t ≲ 13 s; 2 × 1020 Nm), a main‐event sequence (13 ≲ t ≲ 38 s; 2.2 × 1021 Nm), and a terminal sequence (38 ≲ t ≲ 50 s; 3 × 1020 Nm). The main event is resolved into five subevents with peaks at ∼ 16, 20, 26, 29, and 36 s. The spatial pattern of moment release suggests that the main event was confined to the cold slab core, while the initial and terminal stages were part of a distinct westward‐propagating rupture in the lower reaches of the former oceanic plate.
An evaluation of the spatial and interannual variability of tropical precipitation as simulated by GCMs
Authors: Srinivasan G. , Hulme M. , Jones C. G.
Published: February 2004

Precipitation is one of the most difficult variables to simulate in a General Circulation Model and arguably one of the most important. The Atmospheric Model Intercomparison Project (AMIP) provides an opportunity to examine the simulation of precipitation in a wide array of models. Monthly precipitation fields produced by a subset of 19 currently available AMIP model experiments are evaluated for the tropical region using a land‐only observed dataset for the period 1980–1988. The models show large variations in their ability to reproduce observed tropical precipitation, although spatial correlations indicate that some of the models simulate the pattern of observed precipitation fields fairly well. The correlations are strongest during boreal winter (DJF) and weakest during the boreal summer (JJA). Comparison between model and observed precipitation time series for two Central Pacific locations show that most models are unable to reliably reproduce interannual precipitation variability in this region.
Combining groups of paleomagnetic directions or poles
Authors: McFadden P. L. , McElhinny M. W.
Published: February 2004

A simple method is derived for combining the results from m groups of paleomagnetic directions or poles where the groups may have widely differing numbers and where the resultant vectors for the individual groups are not known. Numerical experiments with Fisher distributions show that, given a reasonable number of group means, surprisingly reliable values for R can be obtained even if the group precisions vary widely. An important advantage of this method is that one does not have to consider whether each group by itself is sufficient to average secular variation. Even a single VGP can be included as one of the groups. As an example the method is applied to combining the Cretaceous poles for North America.
Microscopic analysis of macroscopic transport properties of single natural fractures using graph theory algorithms
Authors: Yang Gemei , Myer Larry R. , Brown Stephen R. , Cook Neville G. W.
Published: February 2004

Given an aperture distribution for a single fracture, a graph theory model has been employed to simulate the transport properties of the fracture. In the processes of imbibition and drainage, the connectivity of each phase at a particular capillary pressure can be sought out by the priority‐first search algorithm of graph theory. Then, the flow path in each phase can be identified, and flow equations can be established and solved in an optimal manner. It was observed that in a simulated rough fracture, a few flow “channels” can dominate the permeability of the whole system.
Total solar radiation and the influence of clouds and aerosols on the biologically effective UV
Authors: Bordewijk J. A. , Slaper H. , Reinen H. A. J. M. , Schlamann E.
Published: February 2004

Since clouds and aerosols contribute substantially to the attenuation of biologically effective UV at ground level it is important to consider their role in studies on UV climatology on earth. We describe a method to quantify this attenuation using spectral measurements of UV radiation at ground level and measurements of total solar radiation. The analysis presented gives a very good indication for a non‐linear relation between the attenuation of biologically effective UV on the one hand and total solar radiation on the other. An UV‐climatology can be calculated using the relations found.
Chlorofluorocarbon‐11 removal in anoxic marine waters
Authors: Bullister John L. , Lee Bing‐Sun
Published: February 2004

Measurements of the chlorofluorocarbons CCl3F (F‐11) and CCl2F2 (F‐12) made in the subsurface anoxic zones of the Black Sea and Saanich Inlet, B.C., Canada show a pronounced depletion of dissolved F‐11. These zones are strongly reducing and are characterized by the absence of dissolved nitrate (NO3−) and the presence of hydrogen sulfide (H2S). Models incorporating the atmospheric input histories of these CFCs and the observed distributions are used to estimate residence times for water in these zones and first order in‐situ removal rates for F‐11. In contrast, measurements in the mid‐depth low‐oxygen zone of the eastern Pacific (where NO3− is present and H2S is below detection limits) do not show evidence of similar rapid F‐11 removal.
Multifractal analysis of the Greenland Ice‐Core Project climate data
Authors: Schmitt François , Lovejoy Shaun , Schertzer Daniel
Published: February 2004

Recent climatic records from the Greenland ice‐core project (GRIP) ice core show that the climate proxy temperatures δ18O (18O/16O ratios) display sharp gradients and large fluctuations over all observed scales. We show that these variations are scale invariant over the range ≈400 yr to ≈40 kyr. The fluctuations corresponding to these scales are studied using multifractal analysis techniques. We estimate universal multifractal indices which characterize all the fluctuations for all the scales in this range and which are close to those obtained for turbulent temperatures at much shorter time scales. We speculate briefly on the origin of these common features intervening all over the observed range from seconds to kyr.
The 1994 Bolivia and Tonga events: Fundamentally different types of deep earthquakes?
Authors: Wiens Douglas A. , McGuire Jeffrey J.
Published: February 2004

The 1994 Bolivia and Tonga events show large differences in source and aftershock properties. The Bolivia earthquake, characterized by high stress drop, slow rupture propagation, and a weak aftershock sequence, appears similar to other large deep earthquakes that are isolated from active seismic zones, including the 1970 Colombia earthquake. In contrast, the 1994 Tonga event showed stress drop, rupture propagation velocities, and an aftershock sequence similar to that found for shallow earthquakes. The aftershock sequence of the 1994 Tonga event is many times stronger than has been observed for any other deep earthquake. A survey of deep earthquake aftershocks suggests that aftershock occurrence is correlated with the overall subduction zone magnitude‐frequency relation (b‐value). The largest deep events occur in isolated regions lacking smaller earthquakes, or in subduction zones characterized by anomalously low b‐values. The 1994 Tonga event is an exception and is the largest deep earthquake to occur within an active subduction zone showing a large b‐value, perhaps explaining the strong aftershock sequence. The Bolivia and Tonga events may represent end members of a population of deep earthquakes showing exceptional diversity in source properties, or they may represent two fundamentally different types of deep earthquakes, perhaps resulting from different physical mechanisms.
Determination of the isotropic component of the 1994 Bolivia Deep Earthquake
Authors: Hara Tatsuhiko , Kuge Keiko , Kawakatsu Hitoshi
Published: February 2004

We determine the isotropic component of the moment tensor of the 1994 Bolivia deep earthquake using various seismic waves, including body waves, surface waves, and normal mode data, in the period band between 20 s and 1000 s. We carefully investigate whether the isotropic component can be obtained independently from the other components by checking the correlation matrices. We show that it is possible to obtain a precise estimate of the isotropic component by using normal mode data in the period band between 550 and 1000 s. We find that the Bolivia earthquake did not have a significant isotropic component in this period band.