bluuebunny/crossref_metadata_2025 huggingface dataset:
Bi‐directional electron distributions associated with near‐tail flux transport
Authors: Sergeev V. A. , Baumjohann W. , Shiokawa K.
Published: February 2004

Bi‐directional field‐aligned electron distributions are sometimes observed in the plasma sheet. We looked through AMPTE‐IRM data at high time resolution to study their appearance in the high‐beta plasma sheet between 10 and 15 Re. We found that the occurrence frequency of bi‐directional distributions drops sharply at r ≤ 15Re. We did not observe such anisotropic distributions in the undisturbed plasma sheet, but found them in the locally disturbed central plasma sheet preferentially in the flux tubes with low density and strong magnetic field. No simple association with a specific magnetotail state or substorm phase or rapid flows were observed, but opposite to expectations the largest field‐aligned anisotropy values have been attained during strong magnetic pulse events characterized by the largest magnetic field compression (Bz ≥ 15–20 nT) in which the perpendicular temperature decreased instead of being increased. We study such events to show their identity with plasma bubbles and discuss the reasons why the betatron acceleration is not as effective as Fermi acceleration in these cases. The observations are interpreted in terms of underpopulated newly‐reconnected plasma tubes of limited cross‐tail extent (plasma bubbles) which are produced by impulsive magnetic reconnection and transported to the inner magnetosphere.
Constraints on deep water age and particle flux in the equatorial and South Atlantic Ocean based on seawater 231Pa and 230Th data
Authors: Moran S. B. , Shen C.‐C. , Weinstein S. E. , Hettinger L. H. , Hoff J. H. , Edmonds H. N. , Edwards R. L.
Published: February 2004

High‐precision measurements of 231Pa and 230Th in filtered seawater and suspended particulate matter samples are reported for the Equatorial and South Atlantic. Distributions of 231Pa and 230Th clearly indicate the influence of advection, as evidenced by departures from scavenging models that predict a linear increase with depth for these tracers. Application of a scavenging‐mixing model implies a deep water transit time of ∼60–100 years from the northern source water regions. The average particulate 231Pa/230Th activity ratio is 0.0498±0.0160, a factor of ∼2 lower than the 231Pa/230Th production ratio of 0.093 and in agreement with reported excess 231Pa/230Th ratios of 0.06±0.004 in Holocene sediments north of 50°S in the Atlantic. These water column data further suggest that lateral eddy diffusive transport combined with enhanced scavenging in high‐particle flux marginal regions (boundary scavenging) is weakly expressed in the Atlantic. Particle fractionation of these tracers is also indicated by the elevated fractionation factors of FTh/Pa=4.32–24.04 (ave.=9.97±4.98) compared to values of ∼1–4 in the Southern Ocean.
Isotropy overlying anisotropy at the top of the inner core
Authors: Ouzounis Aristeidis , Creager Kenneth C.
Published: February 2004

We investigate the existence of anisotropy near the top of the inner core under the western hemisphere using differential travel times of pole‐parallel PKPcd‐PKPdf phase pairs and comparisons to equatorial data. We invert a large dataset of PKP differential travel‐time residuals in the same region for a layered model of inner core anisotropy. Our analysis shows that the uppermost 50–150 km of the inner core in this region is isotropic. This implies that anisotropy at greater depths is higher than previous estimates, perhaps as high as 5%. The transition from isotropy to strong anisotropy is modeled as a discontinuity, but a broad transition zone is not excluded by the data. We offer several possible mechanisms for the existence of a layered structure of anisotropy.
New evidence of Tasmania's tectonic history from a novel seismic experiment
Authors: Rawlinson N. , Houseman G. A. , Collins C. D. N. , Drummond B. J.
Published: February 2004

In March 1995, 44 land‐based recorders were deployed throughout Tasmania, SE Australia, to record seismic energy from an encircling array of marine normal‐incidence reflection shot lines. We invert refraction and wide‐angle reflection traveltimes for crustal structure, with the principal outcome being a map of the Tasmanian Moho. Key tectonic inferences from this map include: (1) the Arthur Lineament metamorphic belt in NW Tasmania overlies a major change in crustal thickness (over 5 km) and probably represents the NW limit of deformation in Tasmania during the Mid‐Late Cambrian Tyennan Orogeny, (2) thickening of the crust beneath central northern Tasmania may be associated with the juxtaposition of the Eastern and Western Tasmania Terranes during the Mid‐Devonian Tabberabberan Orogeny, and (3) the difference in crustal thickness between the east and west coasts reflects the presence of differing strain regimes during the Cretaceous break‐up of Gondwana.
Altimeter sea state bias: A new look at global range error estimates
Authors: Chapron B. , Vandemark D. , Elfouhaily T. , Thompson D. R. , Gaspar P. , LaBroue S.
Published: February 2004

A nonparametric SSB model, derived using the TOPEX altimeter, is analyzed to show a new decomposition of the form SSB=bHs + f(σo), where b is 0.03 and the function of radar cross section (σo) is an absolute second‐order range correction residing outside the conventional nondimensional SSB model. Expected variability in the dominant bHs term and its ties to the long wave orbital velocity and shorter‐scale slope variances are discussed using a physically‐motivated restatement of recent EM bias theory. The geometry of steep near‐breaking waves, neglected within current theory, is invoked as one plausible explanation for the observed Hs‐independent SSB component.
Formation of a basin‐scale surface chlorophyll pattern by Rossby waves
Authors: Kawamiya Michio , Oschlies Andreas
Published: February 2004

The enhancement of surface chlorophyll by Rossby waves, which has recently been detected in bandpass‐filtered ocean color data [Cipollini et al., 2001; Uz et al., 2001], is shown to be intense enough to form a dominant pattern in monthly mean basin‐scale ocean color satellite maps of the Indian Ocean. Results from a biological‐physical coupled model suggest that this phenomenon, which is visible predominantly in austral winter, is caused by Rossby‐wave induced upwelling that lifts the deep chlorophyll maximum (DCM) into contact with the surface mixed layer (ML). The model results suggest that these events are not associated with any significant input of nutrients into the ML. While the temporal enhancement of regional primary production by Rossby waves is substantial (∼30%), it is not necessarily associated with a corresponding increase in surface chlorophyll, e.g., when the ML is too shallow to touch the DCM, and may hence escape detectability by satellite measurements.
Three‐dimensional MHD simulations of the Earth's magnetosphere on Feb 9–10 1995 for northward interplanetary magnetic field and comparison of the lobe field with Geotail observations
Authors: Shao X. , Guzdar P. N. , Papadopoulos K. , Goodrich C. C. , Sharma A. S. , Milikh G. M. , Wiltberger M. J. , Lyon J. G.
Published: February 2004

Three‐dimensional Global magnetohydrodynamic simulations of the quiet‐time magnetosphere are compared to data obtained from the Geotail satellite. For the specific event on Feb. 9–10, 1995 when the interplanetary magnetic field was quiet northward and Geotail was in the vicinity of the equatorial plane and around x=−20 RE, the lobe field was found to be steady for 2.5 hours. During the time interval between UT 00:30, Feb. 10 and UT 3:00, Feb. 10, the lobe field Bx is nearly zero and Bz is around 5 nT which is comparable to the Bz (about 5 nT) of the IMF. This is consistent with predictions from our recent steady‐state simulations [Guzdar et al., 2001]. Also performing real event simulations using the global MHD code we find that the time scale for the temporal evolution and magnitude of the the various components of the lobe field agree well with Geotail observations.
Effects of stabilizing atmospheric CO2 on global climate in the next two centuries
Authors: Dai Aiguo , Wigley T. M. L. , Meehl G. A. , Washington W. M.
Published: February 2004

Previous coupled ocean‐atmosphere model simulations showed that the reduction in global warming is only moderate by year 2100 under CO2 stabilization (STA) scenarios compared with that under business‐as‐usual (BAU) scenarios. To further illustrate the long‐term effect of stabilizing CO2 on global climate, we integrated a coupled ocean‐atmosphere model from 1870 to 2200 forced by historical and projected CO2, SO2 and other greenhouse gases under newly updated BAU and STA scenarios. Our results show that the reduction in global warming resulting from CO2 stabilization could be large (∼1.5°C globally, and up to 12°C in DJF at northern high‐latitudes) by the later part of the 22nd century. Stabilizing the CO2 level also results in reduced changes in precipitation, soil moisture and diurnal temperature range. BAU and STA patterns of change are similar for all variables examined.
Separation of intrinsic and scattering Q for volcanic tremor: An application to Etna and Masaya volcanoes
Authors: Del Pezzo Edoardo , Bianco Francesca , Saccorotti Gilberto
Published: February 2004

The energy transfer theory in the hypothesis of 2‐D isotropic multiple scattering is applied to the propagation of volcanic tremor. Under the assumption of a time stationary energy source, we calculate the pattern of energy vs distance as a function of intrinsic and scattering Q. Experimental values of attenuation coefficient
measured at Etna and Masaya Volcanoes are fitted to the theory in order to contemporaneously estimate the loss of energy associated to scattering processes and that produced by intrinsic dissipation. Despite the high degree of trade off between the estimate of intrinsic and scattering attenuation deduced by the data analysis, results indicate that the tremor energy decay with distance is more strongly controlled by intrinsic dissipation than by scattering.
Simulation of the anomalous cosmic ray radiation belt with atmospheric production and decay
Authors: Selesnick R. S.
Published: February 2004

A numerical simulation of the anomalous cosmic ray (ACR) radiation belt, including production by electron stripping and decay by energy loss in a model atmosphere, predicts altitude and time variations over the last solar cycle. Satellite ACR data are used to estimate the unknown trapping cross sections. Energy loss to free electrons is significant for the high altitude trapped ACR which have not yet been observed.
On remote sensing of vertical shear of ocean surface currents by means of a Single‐frequency VHF radar
Authors: Shrira Victor I. , Ivonin Dmitry V. , Broche Pierre , de Maistre Jean C.
Published: February 2004

We propose and test experimentally a new way of probing vertical shear of ocean surface currents by means of a single frequency VHF radar. The key idea is to use additional information provided by the so called secondary peaks in radar echo spectra which appear due to nonlinearity. Results of the field experiment carried out in the Rhône's delta show that the new method does enable one to probe the vertical shear with a reasonable accuracy and has potential for further development.
Can the 1D viscosity profiles inferred from postglacial rebound data be affected by lateral viscosity variations in the tectosphere?
Authors: Martinec Zdeněk , Čadek Ondřej , Fleitout Luce
Published: February 2004

We have tested the impact of lateral viscosity variations (LVV) in the top 200 km of the mantle (tectosphere) on the interpretation of Fennoscandian postglacial uplift data in terms of 1D viscosity models. Our test consists of two steps. In the first step, we simulate the postglacial uplift for a given 2D viscosity structure involving a cratonic lithospheric root below the ice sheet and an asthenosphere below oceanic areas. In the second step, we interpret the result of this simulation in terms of a 1D viscosity model. The resultant 1D viscosity model shows a lower viscosity in the lower mantle, a higher viscosity in the shallow sublithospheric mantle and a smaller thickness of the lithosphere than the synthetic model of viscosity.
Effect of wind on the rise height of volcanic plumes
Authors: Bursik M.
Published: February 2004

A theoretical model of a volcanic plume, based on applying the equations of motion in a plume‐centered coordinate system, suggests that the interaction between a volcanic plume and wind causes enhanced entrainment of air and horizontal momentum, plume bending, and a decrease in plume rise height at constant eruption rate. Because of rapid dilution in the high windspeeds of the polar jet, plumes that vary over more than one order of magnitude in mass eruption rate (106 to 107–108 kg/s), if injected into the polar jet, may all attain rise heights only slightly different from that of the core of the jet, ∼ 10 km, as opposed to 17–33 km in a still atmosphere.
Stability field of new hydrous phase, δ‐AlOOH, with implications for water transport into the deep mantle
Authors: Ohtani Eiji , Litasov Konstantin , Suzuki Akio , Kondo Tadashi
Published: February 2004

We report stability field of a new hydrous phase δ‐AlOOH, which is a high pressure polymorph of diaspore. This phase is stable at pressures from 17 GPa to at least up 25 GPa at around 1000 to 1200°C, which are likely conditions expected in the slabs descending into the lower mantle. This phase contains significant amounts of octahedrally coordinated Mg and Si in solid solution. The oxygen arrangement of δ‐AlOOH is similar to that of the post‐stishovite phase, CaCl2 type SiO2, which exists in the deep lower mantle. δ‐AlOOH may play an important role as a water reservoir in subducting slabs.
Pickup ion acceleration by turbulent electric fields in the slow solar wind
Authors: le Roux Jakobus A. , Matthaeus William H. , Zank Gary P.
Published: February 2004

Recent spacecraft observations reveal that energetic tails in ion spectra are present continually in the slow low‐latitude solar wind, even in the absence of nearby shocks. To explain this phenomenon we take into account growing evidence that MHD turbulence in the solar wind has a strong two‐dimensional (2D) component. 2D MHD turbulence simulations exhibit large‐scale field‐aligned electric field fluctuations which are also observable in the solar wind. We explore pickup ion propagation and acceleration between the Sun and Earth with a newly developed kinetic numerical model which includes a random distribution of large‐scale field‐aligned electric field fluctuations consistent with observations in the low‐latitude solar wind. The model is found to qualitatively reproduce the accelerated interstellar pickup He+spectra observed at Earth. Like the observations, the simulated accelerated “tail” is approximately a power lawf(υ) ∝ υ−4.5until it reaches particle speeds about ten times the solar wind speed where a rollover occurs.
Electrical conductivity and pore‐space topology of Merapi Lavas: Implications for the degassing of porphyritic andesite magmas
Authors: Le Pennec Jean‐Luc , Hermitte Daniel , Dana Isya , Pezard Philippe , Coulon Christian , Cochemé Jean‐Jacques , Mulyadi Eddy , Ollagnier Frédéric , Revest Corinne
Published: February 2004

Pore‐space topology is studied in recent compact angular blocks and scoria fragments from block‐and‐ash flow deposits of Merapi volcano, Indonesia. Connected porosity and electrical conductivity of cored clay‐free samples are measured in the laboratory at varying fluid salinity. The electrical formation factor, tortuosity and cementation index are derived and the pore‐space topology is found to be porosity‐dependent. The electrical flow pattern is controlled by crack‐like paths in compact angular block, and by vesicles geometry in more porous scoria fragments. Because Merapi lavas are highly viscous and crystal‐rich, we infer that the development of pore connectedness and vesicle coalescence is promoted by shear strain. Along with ascent rate considerations we conclude that degassing of Merapi magma occurs mostly in the conduit during ascent.
Scale‐dependence of seismic energy‐to‐moment ratio for strike‐slip earthquakes in Japan
Authors: Izutani Yasuo , Kanamori Hiroo
Published: February 2004

We analyzed four pairs of a large (Mw ≈ 6) and a small (Mw ≈ 3.5 to 4) shallow strike‐slip earthquakes to investigate the scale‐dependence of the seismic energy‐to‐moment ratio, an important macroscopic parameter which reflects the basic physical process of seismic slip. These earthquakes occurred in the south‐western part of Japan, and high‐quality close‐in records (epicentral distance < 50 km) are available for both the small and large earthquakes. The paired events have almost the same focal mechanism and hypocenter location. We used the spectral ratio of the paired events in order to remove the effects of attenuation along the wave propagation path and the station site response. We then estimated the seismic energy from the source spectra estimated from the spectral ratio. The energy‐to‐moment ratio increases with the earthquake size. This scale‐dependence is very similar to that found earlier for earthquakes in Southern California.
Interferometric and dual beam observations of daytime Spread‐F‐like irregularities over Jicamarca
Authors: Chau Jorge L. , Woodman Ronald F.
Published: February 2004

We report new observations made on April 11 2000 over Jicamarca of daytime spread‐F‐like irregularities. These irregularities are extremely rare and were first reported by Woodman et al. [1985]. The main features of these new observations, which are similar to the previous ones, are that they were: (1) two orders of magnitude stronger than the incoherent scatter echoes at the F peak, (2) observed between 1400 and 1600 LT; (3) characterized by small Doppler shifts (|υd| < 1 m s−1); and (4) characterized by long correlation times, i.e., narrow spectral widths. The latter is interpreted as evidence that these irregularities are field aligned (very aspect sensitive in the north‐south direction). On this occasion the irregularities occurred at higher altitudes than before, between 950 and 1450 km compared to 600–1000 km. The echoes in these recent observations were quite localized in the east‐west direction (they were much stronger in the west beam than in the east beam). Furthermore, using interferometry we determined that the irregularities were in the form of blobs, aspect sensitive in the east‐west (as well as north‐south) direction with aspect angle widths as small as 0.2 degrees, particularly when the echoes were strong.
Accurate, direct measurements of oh yields from gas‐phase ozone‐alkene reactions using anin situLIF Instrument
Authors: Kroll Jesse H. , Hanisco Thomas F. , Donahue Neil M. , Demerjian Kenneth L. , Anderson James G.
Published: February 2004

We present direct, pressure‐dependent measurements of OH yields from gas‐phase ozone‐alkene reactions, using the Harvard HOxinstrument to obtain sensitive, accurate, and precise OH concentrations. As in previous studies from our laboratory, steady‐state [OH] is measured by laser‐induced fluorescence (LIF); here, the accurate LIF calibration allows us to present absolute OH yields for the first time. To calibrate our original LIF system, we measure yields from ozone plus tetramethylethylene (TME) as a function of pressure. The pressure dependence agrees with our previous results, so our yield measurements are now of comparable accuracy to those from indirect studies. Prompt, low‐pressure yields agree well with 1 atm yields measured over longer timescales, confirming that much of the OH arises from decomposition of stabilized carbonyl oxides. We also explore the pressure dependence of yields from ethene, isobutene, and isoprene. Yields from isobutene and isoprene are pressure‐dependent, consistent with the formation of substituted carbonyl oxides. We observe no pressure dependence of the OH yield from ozone + ethene, finding instead a constant yield of 14%, in line with most 1 atm studies but in contrast with the results of another pressure‐dependent study.
Sunset observations of ClO in the Arctic Polar Vortex and implications for ozone loss
Authors: Vömel H. , Toohey D. W. , Deshler T. , Kröger C.
Published: February 2004

Chlorine oxide (ClO) was measured in situ in the perturbed arctic vortex from a balloon launched near Kiruna, Sweden, 67°N, at sunset on January 27, 2000. Between 20 and 23 km, the time‐dependent behavior of ClO agrees with the functional form for the kinetics of ClO + ClO + M → Cl2O2 + M. The temporal change of ClO is described well by the integral of a rate expression that includes this reaction and thermal decomposition of Cl2O2. The value for the rate coefficient that best describes the observed decreases in ClO is consistent with the upper limit of the currently recommended value, and agrees well with the results of a recent laboratory study of ClO recombination at 190–195 K. These results reinforce the link between man‐made chlorine compounds and ozone losses in the polar regions.
A simplified model of the water soluble organic component of atmospheric aerosols
Authors: Fuzzi S. , Decesari S. , Facchini M. C. , Matta E. , Mircea M. , Tagliavini E.
Published: February 2004

The properties of atmospheric aerosol organic compounds are often simulated in models by arbitrarily choosing model compounds which have, in most cases, little contact with the physical reality. We propose here a procedure with which to derive a simplified model of the water soluble organic fraction of the atmospheric aerosol. Quantitative measurements of organic carbon concentration and proton concentration of the main functional groups contained in the aerosol water soluble organic compounds (WSOC) mixture are used to formulate a set of a few model compounds, representative of the whole WSOC mass, which can simulate in models the chemical and physical properties of aerosol WSOC.
The effects of temperature, pressure, and alteration on seismic properties of diabase dike rocks from DSDP/ODP Hole 504B
Authors: Carlson R. L.
Published: February 2004

A 0.4 to 0.5 s−1 in situ vertical velocity gradient in the diabase dike section of DSDP/ODP Hole 504B has been attributed to the effects of increasing pressure and downhole changes of mineralogy caused by hydrothermal alteration. An analysis of velocities measured in diabase samples as a function of pressure shows that increasing pressure accounts for a gradient of at most 0.1 s−1. Neither laboratory data nor a Voigt‐Reuss‐Hill average velocity model in which Vp pyx > Vp amph shows a significant variation of velocity with depth; composition and pressure combined account for a gradient not greater than 0.2 s−1. These results indicate that either the elastic moduli of the amphibole minerals in these rocks are higher than those of the pyroxene phase (Vp amph > Vp pyx,) or the seismic properties of the dikes are affected by a network of thin, large‐scale cracks.
Links between intraseasonal (extended MJO) and ENSO timescales: Insights via geodetic and atmospheric analysis
Authors: Marcus Steven L. , Dickey Jean O. , de Viron Olivier
Published: February 2004

The relationship of intraseasonal variability to ENSO is investigated using daily length‐of‐day (LOD), atmospheric angular momentum (AAM), west equatorial Pacific (WPAC) wind stress and monthly Nino3 SST data for the years 1976–1999. Strong coherence is found for LOD, AAM, and their residual (representative of oceanic angular momentum and / or unmodeled/underrepresented atmospheric variability) with the regional wind stress at periods near 75 days, a preferred time scale for WPAC Kelvin wave generation. Amplitude envelopes of LOD and AAM filtered at similar periods (60–100 days) are significantly correlated with Nino3 anomalies at an SST lag of 8 months; the LOD‐AAM residual correlates at a shorter lag (5 months), with the difference representing an oceanic spin‐up time. No significant correlations are found using a band (36–60 days) typifying the global Madden‐Julian Oscillation, accounting for the lack of previous MJO‐ENSO correlations in the literature.
Highly elevated methane in the eastern tropical North Pacific and associated isotopically enriched fluxes to the atmosphere
Authors: Sansone Francis J. , Popp Brian N. , Gasc Anne , Graham Andrew W. , Rust Terri M.
Published: February 2004

During the May ‐ June, 2000 Eastern Pacific Redox Experiment (EPREX) we examined the dynamics of methane (CH4) in the eastern tropical North Pacific (ETNP), a large region of high surface‐ocean productivity fueled by coastal upwelling. We discovered that (1) the ETNP contains by far the largest pool of CH4 yet discovered in the open ocean; (2) CH4 production in the upper half of this subsurface pool is associated with the decomposition of locally produced sinking particulate matter; (3) the deeper half of this pool is from a coastal source; (4) advection and oxidation of the upper pool leads to the heavy CH4 isotopic values seen at midwater in the North Pacific subtropical gyre; and (5) the ETNP is a source of isotopically enriched CH4 to the atmosphere. Our results suggest that other oceanic areas of upwelling‐induced anoxia may be sites of significant atmospheric input of isotopically heavy CH4.
Observations of APAN during TexAQS 2000
Authors: Roberts James M. , Flocke Frank , Weinheimer Andrew , Tanimoto Hiroshi , Jobson Bertram T. , Riemer Daniel , Apel Eric , Atlas Elliot , Donnelly Stephen , Stroud Verity , Johnson Kristen , Weaver Rachel , Fehsenfeld Fredrick C.
Published: February 2004

Measurements of peroxycarboxylic nitric anhydrides (PANs) made in Houston, Texas during TexAQS (Texas Air Quality Study) 2000 showed a relatively abundant PAN compound that had not been identified in previous studies in North America [cf. Williams et al., 2000]. This compound was hypothesized to be peroxyacrylic nitric anhydride {CH2=CH‐C(O)OONO2, APAN} based on the work of Tanimoto and Akimoto, [2001]. APAN was synthesized and characterized on one of the two GC systems used to make those measurements, subsequent to the TexAQS 2000 field study, confirming that APAN was observed during TexAQS 2000, both on the ground and in airborne measurements. Mixing ratios of APAN were estimated from the response of the system to PAN and PPN and ranged up to 502 pptv, which was 30% of PAN. High APAN values were associated with the precursor species 1,3‐butadiene and acrolein, which had local petrochemical sources. The presence of APAN at these unprecedented levels demonstrates the impact of these reactive VOC species, and may have associated health effects.
A new approach to investigate the correlation between geoelectrical time fluctuations and earthquakes in a seismic area of southern Italy
Authors: Telesca Luciano , Cuomo Vincenzo , Lapenna Vincenzo , Macchiato Maria
Published: February 2004

We propose a new approach to investigate the possible correlation between electrical signals and earthquakes. Good correlation has been found between the spectral power‐law exponent of geoelectrical signals and the Hurst exponent of the seismicity of the area investigated. A tendency of both parameters to converge toward unity, typical of self‐organized critical dynamics, is evident before the occurrence of the major event recorded in the area during the observation period.
Forward mechanical modeling of the Amenthes Rupes Thrust Fault on Mars
Authors: Schultz Richard A. , Watters Thomas R.
Published: February 2004

Amenthes Rupes overlies one of the largest thrust faults on Mars, with structural topography accurately measured by MOLA. Forward mechanical models successfully predict the surface topography across this large contractional structure. The best‐fitting fault parameters are: fault dip angle, 25‐30°; depth of faulting, 25‐30 km; and fault offset, 1.5 km. These first‐order results are insensitive to either the offset distribution along the fault or crustal material properties. Both very shallow (e.g., ∼15 km) and very deep (∼45 km) depths of faulting can be ruled out, as can significantly different dips and offset magnitudes. Amenthes Rupes may span the ancient seismogenic lithosphere in the Martian Noachian highlands, implying maximum values at the time of faulting for heat flux of ∼54‐70 mW m−2 and paleogeothermal gradient of 15‐20 K km−1.
Modal scattering: A key to understanding oceanic T‐waves
Authors: Park Minkyu , Odom Robert I. , Soukup Darin J.
Published: February 2004

The excitation mechanism of oceanic T‐waves has been a puzzle for almost fifty years, with refraction from a sloping seafloor and seafloor scattering as two of the most commonly invoked mechanisms. By representing the earthquake source field as a normal mode sum, it can be seen that both mechanisms are very closely related. Strict modal orthogonality prohibits the existence of T‐waves in a laterally homogeneous semi‐infinite half‐space or radially symmetric sphere, as energy cannot be transferred from one mode to another in an homogeneous medium. Deterministic non‐planar bathymetry, random boundary roughness, upper crustal heterogeneity, or a combination of these provides a physical mechanism to break the strict orthogonality. We show that modal scattering from the rough seabottom in the epicentral region converts energy from the directly excited ocean crustal/water column modes to the propagating acoustic modes comprising the oceanic T‐wave. Submarine earthquake fault orientation also appears to be reflected in the T‐wave excitation.
Ageostrophic transport in the upper layers of the tropical Atlantic Ocean
Authors: Garzoli Silvia L. , Molinari Robert L.
Published: February 2004

A test of the theoretical Ekman relation in the tropical Atlantic Ocean is performed by comparing estimated Ekman transport with observations collected along two transects symmetric about equator (6°N and 6°S). Ekman transport is calculated theoretically using ship winds and climatological data. Total ageostrophic transport is obtained by subtracting the observed geostrophic transports from the measured total transports using the data collected along the two transects. Along 6°S, both the zonal mean ageostrophic transport and it's variability with longitude can be accounted for by the theoretical Ekman transport. Along 6°N, the total ageostrophic and Ekman transports agree, but significant differences are found in the cumulative transport curves between the African coast and about 40°W. These departures from theory may be related to the effect of advective terms in the Ekman relation and/or other ageostrophic motion at the reference depth for the comparisons. Begin typing abstract here.
Satellite detection of a continental‐scale plume of nitrogen oxides from boreal forest fires
Authors: Spichtinger N. , Wenig M. , James P. , Wagner T. , Platt U. , Stohl A.
Published: February 2004

In previous studies it was shown that boreal forest fires in Canada caused large plumes with high CO and aerosol concentrations in August 1998. Haze and enhanced CO and O3 were observed even over Europe. In this study we use dispersion model calculations, Total Ozone Mapping Spectrometer (TOMS) aerosol index data, and tropospheric NO2 columns derived from Global Ozone Monitoring Experiment (GOME) data to track a NOx plume from forest fire hot spots, via the Atlantic Ocean, to the west coast of Europe.
Locked and creeping patches along the Hayward Fault, California
Authors: Wyss M.
Published: February 2004

The results of mapping locked and unlocked patches on the Hayward fault using the local recurrence time method are compared with models derived from surface creep and geodetic measurements. The data used were the M > 1.0 earthquakes in the USGS catalog since 1981.0, located within 5 km of the fault trace. Along the central and southern segments, agreement with the other methods is satisfactory. The 1868 rupture, except for its two ends, is classified as a locked segment by our method. In the northern part of the Hayward fault, the data are poor and the results of the three methods differ. Short local recurrence times in the northern part suggest that an asperity exists there, which is capable of an M6.5 class event.
A new method for describing long‐term changes in total ozone
Authors: Harris J. M. , Oltmans S. J. , Tans P. P. , Evans R. D. , Quincy D. L.
Published: February 2004

A new method for describing long‐term changes in total ozone was developed so that variations on time scales greater than that of the QBO may be examined. The technique fits a flexible tendency curve to total ozone data after explained variations have been removed. The derivative of the tendency curve is the growth rate curve. The average along this curve is comparable to total ozone trends reported in the past. Statistical uncertainty of the growth rate is determined using bootstrap techniques. Dobson column ozone measurements with long‐term (30+ years) records from the NOAA/CMDL Cooperative Dobson Network were analyzed. Total ozone decreases ranged from 1‐2%/decade since the 1960s and from 2‐4%/decade since 1979 at all sites except Mauna Loa where results were not significant. The tendency curves indicate that the total ozone decline began in the 1970s and that there are no clear signs of recovery as of the end of 2000.
January 1999 Indian Ocean Cooling Event
Authors: Harrison D. E. , Vecchi Gabriel A.
Published: February 2004

Unexpectedly strong sub‐seasonal SST variability over the tropical Indian Ocean has been observed by the TRMM microwave imager, which provides unprecedented tropical SST information in the presence of clouds. In January–February 1999 SST averaged over an area 20° longitude by 10° latitude cooled by ∼1.5°C over 10 days and warmed by ∼1.25°C in the following week. Local changes were up to ±3°C. There were strong variations in atmospheric convection and surface wind stress associated with the SST variability. The evolution of the convection suggests a feedback from the SST changes into atmospheric convection. Net air‐sea heat‐flux cannot account for the observed cooling; oceanic processes are fundamental to this event. The roles of such sub‐seasonal ocean‐atmosphere interactions in the evolution of the Madden‐Julian Oscillation, the seasonal and the interannual variability of Indian Ocean SST deserve further investigation.
Application of a sequential reaction model to PANs and aldehyde measurements in two urban areas
Authors: Roberts James M. , Stroud Craig A. , Jobson Bertram T. , Trainer Michael , Hereid Daniel , Williams Eric , Fehsenfeld Fred , Brune William , Martinez Monica , Harder Hartwig
Published: February 2004

Measurements of the peroxycarboxylic nitric anhydrides (PANs = peroxyacetic nitric anhydride, PAN, peroxypropionic anhydride, PPN, and peroxymethacrylic nitric anhydride, MPAN) and aldehydes (acetaldehyde, propanal, and methacrolein) were made at Nashville, TN. in 1999 and Houston, TX. in 2000. The data were interpreted with a sequential reaction model that included reaction of aldehydes with hydroxyl radical and formation or loss of PANs mediated by peroxyacyl radicals {RC(O)OO}. The comparison of the measured ratios with those predicted by the model showed a disagreement for PAN/acetaldehyde and PPN/propanal in Nashville, but agreement in Houston. The Nashville data set also showed a disagreement in the case of PAN/acetaldehyde and MPAN/methacrolein, but agreement for PPN/propanal and MPAN/methacrolein. These features were consistent with the relative importance of isoprene to PAN formation at each site. The ratios were found to be highly correlated with ozone mixing ratios at each site.
Nonlinear P‐wave tomography of subducted lithosphere beneath central‐southern Apennines (Italy)
Authors: Cimini Giovanni B. , De Gori Pasquale
Published: February 2004

We present new tomographic images for the P‐wave velocity structure in the upper mantle beneath central‐southern Apennines down to 510 km depth. The model is computed by nonlinear inversion of relative arrival times of both direct and secondary teleseismic phases, handpicked from over 2800 waveforms recorded by the Italian seismic network during 1988‐2000. Beneath central Apennines, the images reveal a continuous, SW‐dipping high‐velocity body, from ∼ 150 km down to ∼ 500 km. At shallower depths, a pronounced low‐velocity zone is recognized from the uppermost mantle beneath the Apenninic belt down to ∼ 200 km below the Tyrrhenian area. This feature is proposed to affect the seismic structure of the downgoing slab, weakening its velocity signature. Beneath southern Apennines, high‐velocity anomalies are reconstructed in the uppermost mantle of the Apulian foreland and below the belt in the range 100 ÷ 400 km. Low‐velocity regions, interpreted as due to asthenospheric upwelling, are recovered above or across the fast structures, as at the southeastern end of the Apennines where a possible complete slab breakoff is suggested.
Has northern Indian Ocean Cloud cover changed due to increasing anthropogenic aerosol?
Authors: Norris Joel R.
Published: February 2004

The recent Indian Ocean Experiment (INDOEX) observed high aerosol concentrations with a sizeable soot fraction over the northern Indian Ocean. This aerosol mix substantially absorbs solar radiation, and recent modeling studies have proposed that the resulting atmospheric heating reduces daytime cloud cover. The present study tests this hypothesis by investigating whether low‐level cloud cover has decreased over the northern Indian Ocean between 1952 and 1996, a time period when south Asian anthropogenic emissions have greatly increased. The observed slight increase in cloud cover indicates that other processes must compensate soot solar heating. A similar increase in cloud cover observed over the relatively clean southern Indian Ocean suggests the increase over the northern Indian Ocean does not have a special regional anthropogenic aerosol origin.
Singular spectrum analysis of Baltic Sea ice conditions and large‐scale atmospheric patterns since 1708
Authors: Jevrejeva Svetlana , Moore John C.
Published: February 2004

We examine the relationship between ice conditions in the Baltic Sea and the large‐scale atmospheric circulation patterns that create them. Singular Spectrum Analysis (SSA) is used to extract long‐term trends and quasi‐regular oscillations from time series of winter air temperature, date of ice break‐up, maximum annual ice extent in the Baltic Sea (BMI) since 1708 and seasonal North Atlantic Oscillation (NAO) and Arctic Oscillation (AO) indices. The AO exhibits power at periods of 2.3 and 13.9 years as well as at 7.8 years, and in general the NAO can be viewed as a subset of the AO as regards the Baltic region. Time series of ice break‐up date also reflects variations in winter AO power in the 13.9‐year power band, but not in the NAO 7.8‐year band. The BMI seems to act as a non‐linear filter on the fairly weak climate oscillations, increasing the signal‐to‐noise ratio of the oscillations significantly.
Uptake of Cl and Br by organic surfaces—A perspective on organic aerosols processing by tropospheric oxidants
Authors: Moise Tamar , Rudich Yinon
Published: February 2004

The reactive uptake of Cl and Br atoms by closely packed organic thin films was studied in a flow reactor. For Cl, the reactive uptake coefficient, γ, was near collision rate for alkane and alkene surfaces. For Br, γ =(3±1)×10−2 for alkane and γ=(5±2)×10−2 for alkene surfaces. The processing of the surface was monitored using FTIR, XPS and contact angle measurements. Oxidized surface‐bound products and a concurrent increase in hydrophilicity were observed. The probability of a reactive collision between Br, Cl, O(³P), O3 and NO3 and surface‐bound organics is compared with that of comparable gas‐phase reactions, showing that reactions with a high activation energy in the gas‐phase have an enhanced surface reaction probability. The uptake coefficients for these tropospheric oxidants are used to estimate the processing time for an organic coated aerosol.
Long term measurements of radiation belts by SAMPEX and their variations
Authors: Li Xinlin , Baker D. N. , Kanekal S. G. , Looper M. , Temerin M.
Published: February 2004

The Solar, Anomalous, and Magnetospheric Particle Explorer (SAMPEX), a low‐altitude and polar‐orbiting satellite, has provided a long‐term global picture of the radiation belts since its launch on July 3, 1992. While the inner belt (L < 2) protons appear to have only a solar cycle variation, the outer radiation belt (L > 2) electrons vary on solar cycle, semiannual, and solar rotation time scales, and with geomagnetic storms. Recently developed models of predicting MeV electron at geostationary orbit [Li et al., 2001] and the Dst index [Temerin and Li, 2001] based on solar wind measurements are used to examine the cause of the prominent semiannual variations of outer belt electrons and the Dst index. The equinoctial effect (the angle between the Earth's dipole and the flow direction of the solar wind) contributes most to the semiannual variation of the Dst and MeV electrons deep in the inner magnetosphere (L < 5). The semiannual variation of MeV electrons at geostationary orbit is attributed mostly to the semiannual variation of solar wind velocity.
One Martian year of atmospheric observations by the thermal emission spectrometer
Authors: Smith Michael D. , Pearl John C. , Conrath Barney J. , Christensen Philip R.
Published: February 2004

The Mars Global Surveyor has completed one full Martian year of mapping. Infrared spectra returned by the Thermal Emission Spectrometer (TES) are very well suited for monitoring the thermal structure and the distribution of aerosols and water vapor in the Mars atmosphere. Nadir‐viewing spectra allow a global picture of the state of the Mars atmosphere on a daily basis. We report here on the observed annual cycle of the latitudinal dependence of atmospheric temperature, dust aerosols, water‐ice clouds, and water vapor.
Focussed time‐dependent martian volcanism from chemical differentiation coupled with variable thermal conductivity
Authors: Schott B. , van den Berg A. P. , Yuen D. A.
Published: February 2004

Recently the Orbiter Camera on the Mars Global Surveyor imaged on some lava flows. The sparse cratering and thence young age of these flows indicates that volcanic activity on Mars is long‐lived and perhaps pulsating. These pulses beg for an explanation, not yet provided by one‐dimensional convection models simulating the thermal and compositional evolution of the Martian interior. We have, for the first time, simulated the thermochemical evolution of Mars with a two‐dimensional model for the entire planetary history. Our results show that variable thermal conductivity k(T, P) can maintain sublithospheric “hot spots” over time scales of several hundred Ma and is essential in the focussing of hot mantle upwellings at almost the same location. This scenario can explain the persistent pulsating and focussed volcanism in the Tharsis region.
Simulation of flow and transport in a single fracture: Macroscopic effects of underestimating local head loss
Authors: Nicholl Michael J. , Detwiler Russell L.
Published: February 2004

Fluid flow in a single fracture is commonly simulated using the Reynolds equation. Recent work suggests that this depth‐averaged approach underestimates head loss in regions of changing aperture. Implementing an ad hoc correction in the numerical formulation of the Reynolds equation allows us to modify local head loss, and calibrate simulation results to existing experimental data. Calibrated flow fields provide an improved estimate of longitudinal dispersivity, demonstrating the importance of adequately describing local head loss.
One‐year observations of particle lidar ratio over the tropical Indian Ocean with Raman lidar
Authors: Franke Kathleen , Ansmann Albert , Müller Detlef , Althausen Dietrich , Wagner Frank , Scheele Rinus
Published: February 2004

Observations of the extinction‐to‐backscatter ratio (lidar ratio) of South and Southeast Asian aerosol particles are presented for the wavelength of 532nm. Raman lidar measurements were performed in the Maldives (4.1° N, 73.3° E) in the framework of the Indian Ocean Experiment (INDOEX) in 1999/2000. These observations in the tropics are an important contribution to a growing global lidar‐ratio climatology which is needed for an improved determination of the particle optical depth with ground‐based and spaceborne lidars. The lidar ratio was found to be a useful quantity to trace back different pollution sources and to identify less and considerably light‐absorbing particles. During the winter/spring seasons heavily polluted air from India and Southeast Asia was advected to the lidar site. Under these conditions lidar ratios up to 110sr were observed in the lofted pollution plumes above 1000m height. According to backward trajectories the highest lidar ratios were found for airmasses which crossed the eastern and northeastern parts of India. Large lidar ratios >70sr indicate small, considerably absorbing aerosol particles. Below 1000m height, the lidar ratio typically ranged from 30‐60sr. The marine boundary layer contained a mixture of marine and anthropogenic particles. Under clean, marine conditions in October 1999, lidar ratios <30sr were found.
Plasma density distribution along the magnetospheric field: RPI observations from IMAGE
Authors: Reinisch B. W. , Huang X. , Song P. , Sales G. S. , Fung S. F. , Green J. L. , Gallagher D. L. , Vasyliunas V. M.
Published: February 2004

A new technique is introduced that remotely measures the plasma density profile in the plasmasphere. Radio plasma imager (RPI) echo observations provide echo delay time as function of frequency, from which the plasma density as function of position along the magnetic field line can be calculated. An example from the nightside plasmasphere (L=3) shows the density having its minimum value near the equator and rapidly increasing densities along the field line above 40° magnetic latitude. The density increases at a faster rate toward the ionosphere than the field strength. The index of the power law of the density as a function of field strength increases from a few tenths near the equator to close to unity near 40° and greater than 2 near the ionosphere.
Average aerosol extinction and water vapor profiles over the Southern Great Plains
Authors: Turner D. D. , Ferrare R. A. , Brasseur L. A.
Published: February 2004

An operational Raman lidar deployed at the DOE Atmospheric Radiation Measurement site in Oklahoma has collected more than 7500 h of aerosol and water vapor data between April 1998 and January 2000. These data, which span a wide variety of atmospheric conditions, have been analyzed as a function of season, integrated amount, and time of day. The scale height of the mean aerosol profiles varies considerably as both a function of season and aerosol optical thickness, with the mean scale height increasing from less than 1 km in the winter to over 2 km during turbid summer days. The mean scale height of the water vapor remained very close to 2 km, regardless of season or precipitable water vapor. Furthermore, the distribution of aerosol optical thickness shows a slight shift to smaller values at night compared to day, and the mean aerosol profiles show little diurnal dependence except at the top of the boundary layer.
Dynamical response of equatorial Indian Ocean to intraseasonal winds: Zonal Flow
Authors: Han Weiqing , Lawrence David M. , Webster Peter J.
Published: February 2004

Nonlinear and linear 4½‐layer ocean models are used to explore the dynamics of intraseasonal (20–90 day periods) zonal flow in the equatorial Indian Ocean. The model simulations suggest that the observed 40–60 day zonal surface current is forced primarily by wind associated with the Madden‐Julian Oscillation (MJO), which peaks at 40–60 days. The strongest spectral peak of zonal flow, however, occurs at 90‐day period in the model and a corresponding 90‐day peak appears in the observed sea level data. The 90‐day current results from the preferential excitation of Kelvin and Rossby waves by the lower‐frequency component of intraseasonal wind and from the enhancement by Rossby waves reflected from the eastern ocean boundary.