bluuebunny/crossref_metadata_2025 huggingface dataset:
Obtaining the Shear Stress versus Shear Rate Relationship and Yield Stress of Blood from Capillary Viscometry Data by Tikhonov Regularization
Authors: Yeow Y. Leong , Leong Yee‐Kwong , Wickramasinghe S. Ranil , Han Binbing
Published: September 2002

This paper describes a procedure, based on Tikhonov regularization, for extracting the shear stress versus shear rate relationship and yield stress of blood from capillary viscometry data. The relevant equations and the mathematical nature of the problem are briefly described. The procedure is then applied to three sets of capillary viscometry data of blood taken from the literature. From each data set the procedure computes the complete shear stress versus shear rate relationship and the yield stress. Since the procedure does not rely on any assumed constitutive equation, the computed rheological properties are therefore model‐independent. These properties are compared against one another and against independent measurements. They are found to be in good agreement for shear stress greater than 0.1 Pa but show significant deviations for shear stress below this level. A possible way of improving this situation is discussed.
Improved Performance of Preordered Fungal Protease‐Stearic Acid Biocomposites: Enhanced Catalytic Activity, Reusability, and Temporal Stability
Authors: Phadtare Sumant , Dash Chandravanu , Gole Anand , Vinod V. P. , Rao Mala , Sastry Murali
Published: September 2002

In an earlier report on fungal protease (F‐prot)–fatty acid biocomposite film formation [Gole et al. Anal. Chem. 2000, 72, 4301], it was observed that the biocatalytic activity of the immobilized enzyme was comparable to that of the free enzyme in solution. However, a somewhat negative aspect of the protocol was the steady loss in activity during reuse and storage of the biocomposite film. In this paper, we address the latter issues and demonstrate successful attempts toward the realization of efficient biocomposite films with enhanced biological activity, temporal stability, and excellent reusability. The improved performance of the F‐prot‐stearic acid biocomposite is accomplished by preordering the fatty acid film by incorporation of Pb2+ions into the lipid matrix prior to enzyme immobilization. The lead cation induces lamellar ordering in the lipid film and thus facilitates diffusion of the F‐prot molecules into the lipid matrix and accessibility of the substrate molecules (hemoglobin, Hb) to the entrapped F‐prot enzyme molecules. The preordering consequently leads to effective control of the “mass transport” problem and might be responsible for the enhanced biological activity (∼ 36%) of the enzyme molecules in the biocomposite in comparison with the free enzyme in solution, as well the excellent reusability of the composite film. In addition to biocatalytic activity measurements, the formation and characterization of the F‐prot‐lead stearate biocomposite films was done by quartz crystal microgravimetry and X‐ray diffraction.
Rinaldo receives 1999 Research Award
Authors: Rodriguez‐Iturbe Ignacio , Rinaldo Andrea
Published: September 2002

Andrea Rinaldo received the 1999 Research Award, presented by the Hydrology Section during the 1999 AGU Fall Meeting. The award recognizes an outstanding contribution to the science of hydrology.
New Io data spur discussion on ultrabasic lavas
Authors: Williams David A. , Keszthelyi Laszlo , Stansberry John
Published: September 2002

In the late 1960s, the Viljoen brothers identified a new class of igneous rock in the ancient (3.5 Ga) Barberton greenstone belt of South Africa. Called komatiites, after the Komati River that flows nearby, these new rocks were soon recognized in Precambrian terrains around the world as the metamorphosed remnants of ancient ultrabasic lava flows and shallow intrusions, the extrusive equivalent of peridotites. Komatiites, although rare in the geologic record, soon became of interest to a wide variety of geologists because of their unique texture, composition, and physical properties, and their genetic association with massive nickel sulfide ore deposits.

With recognition of the inferred high temperature, low viscosity turbulent emplacement, and great thermal erosive potential of these lavas, komatiites became an analog to low‐viscosity extraterrestrial lavas, which formed long, sinuous lava channels and flow fields on the Moon,Venus, Mars, and Io. Now, with indications from the Galileo spacecraft and other instruments that active volcanism on Jupiter's moon, lo,may include ultrabasic eruptions, there is renewed interest in understanding the nature of komatiite lavas and what they can tell us about the thermal‐compositional‐physical dynamics of the early Earth, and perhaps other planets as well.
Methane flux in subalpine wetland and unsaturated soils in the southern Rocky Mountains
Authors: Wickland Kimberly P. , Striegl Robert G. , Schmidt Steven K. , Mast M. Alisa
Published: September 2002

Methane exchange between the atmosphere and subalpine wetland and unsaturated soils was evaluated over a 15‐month period during 1995–1996. Four vegetation community types along a moisture gradient (wetland, moist‐grassy, moist‐mossy, and dry) were included in a 100 m sampling transect situated at 3200 m elevation in Rocky Mountain National Park, Colorado. Methane fluxes and soil temperature were measured during snow‐free and snow‐covered periods, and soil moisture content was measured during snow‐free periods. The range of mean measured fluxes through all seasons (a positive value represents CH4 efflux to the atmosphere) were: 0.3 to 29.2 mmol CH4 m−2 d−1 wetland area; 0.1 to 1.8 mmol CH4 m−2 d−1, moist‐grassy area; −0.04 to 0.7 mmol CH4 m−2 d−1, moist‐mossy area; and −0.6 to 0 mmol CH4m−2 d−1, dry area. Methane efflux was significantly correlated with soil temperature (5 cm) at the continuously saturated wetland area during snow‐free periods. Consumption of atmospheric methane was significantly correlated with moisture content in the upper 5 cm of soil at the dry area. A model based on the wetland flux‐temperature relationship estimated an annual methane emission of 2.53 mol CH4 m−2 from the wetland. Estimates of annual methane flux based on field measurements at the other sites were 0.12 mol CH4 m−2, moist‐grassy area; 0.03 mol CH4 m−2, moist‐mossy area; and −0.04 mol CH4 m−2, dry area. Methane fluxes during snow‐covered periods were responsible for 25, 73, 23, and 43% of the annual fluxes at the wetland, moist‐grassy, moist‐mossy, and dry sites, respectively.
Epochal changes in Indian Monsoon‐ENSO precursors
Authors: Kumar K. Krishna , Kleeman R. , Cane Mark A. , Rajagopalan Balaji
Published: September 2002

Precursors for the Indian monsoon are known to be highly epoch specific in their skills in predicting the monsoon on seasonal time scales. We show that the various precursors are correlated with the monsoon, only when they are correlated with ENSO, which happened in the recent period 1951–1990, but not in the 1990's and the period 1911–50. This accounts for the skill in monsoon prediction during 1951–90. We find that ENSO and its precursors tend toward higher amplitude and 3–5 year periods in the 1951–1990 epoch, and toward decreased amplitude and 5–7 year periods in the 1911–1950 epoch. We argue that the shift to lower frequency and amplitude in the earlier epoch diminished the association between the monsoon precursors and ENSO, leading to diminished skill in predicting the monsoon in that epoch. However, the simultaneous relationship between the monsoon and ENSO has been stable over the past 140 years, suggesting that the monsoon—ENSO teleconnections are robust once ENSO is established. Changes in the frequency of ENSO have implications for statistical prediction schemes for ENSO and the monsoon.
An ocean modeling study of the Cenomanian Atlantic: Equatorial paleo‐upwelling, organic‐rich sediments and the consequences for a connection between the proto‐North and South Atlantic
Authors: Handoh Itsuki C. , Bigg Grant R. , Jones E. John W. , Inoue Masamichi
Published: September 2002

A reduced‐gravity ocean model is used to determine the pattern of upwelling in the Cenomanian Atlantic. The deposition of organic‐rich sediments on the margins of the equatorial region is found to be consistent with the patterns of upwelling in simulations which incorporate only a shallow (≤300m) equatorial connection between the North and South Atlantic. Fracture zone ridges were probably responsible for the effective shallowness of the gateway. If a deep equatorial channel is assumed the modeling results are consistent only with the more recent, Turonian, sedimentary record. We suggest, therefore, that reduced‐gravity models provide a mean of predicting areas of the continental margins which may be underlain by hydrocarbon‐rich sedimentary rocks.
On the origin of step‐pool sequences in mountain streams
Authors: Chin Anne
Published: September 2002

This paper reports a field test of the prevailing antidune theory to explain the mechanisms of step‐pool formation in steep mountain streams. The theory is supported by laboratory data but it has not received extensive field testing that would enable wide applicability to natural conditions. Data from the Santa Monica Mountains of California are used to test the antidune model where step wavelength and reconstructed hydraulic conditions are compared with the formation domain predicted by experimental and theoretical studies. Results show general agreement between field and laboratory data. Step wavelength and hydraulic requirements are consistent with those of the antidune process of formation, but results also suggest that true antidunes may be difficult to achieve in the steep headwaters where channels may be dominated by large roughness elements. These findings strengthen the link between theory and observation in clarifying how step‐pools form; they contribute to the basis for elucidating why step‐pools form in mountain streams.
Jovian dual‐sinusoidal HOM Lane features observed by Galileo
Authors: Higgins Charles A. , Thieman James R. , Fung Shing F. , Green James L. , Candey Robert M.
Published: September 2002

A well defined sinusoidal‐shaped “band” of reduced emission intensity exists within Jovian HOM from 500 kHz to 3 MHz at all Jovian longitudes as observed by the Galileo spacecraft. A less prominent sinusoidal‐shaped band feature exists in the same frequency range but is 180° out of phase with the more prominent feature. We used a multiple Jovian rotation spectrogram technique to fully display both bands and found that these sinusoidal‐shaped features are the source of the “lanes” previously studied in Voyager and Ulysses data. Our extension of the simple straight‐line ray model by Gurnett et al. [1998] provides a qualitative explanation for the observed features. We found that the two sinusoidal bands show an asymmetry about the longitude of the northern tip of the magnetic dipole (202° CML). Enhancements of emission can be seen along the edges of the bands which may be interpreted as caustic surfaces.
Global rural temperature trends
Authors: Peterson Thomas C. , Gallo Kevin P. , Lawrimore Jay , Owen Timothy W. , Huang Alex , McKittrick David A.
Published: September 2002

Using rural/urban land surface classifications derived from maps and satellite observed nighttime surface lights, global mean land surface air temperature time series were created using data from all weather observing stations in a global temperature data base and from rural stations only. The global rural temperature time series and trends are very similar to those derived from the full data set. Therefore, the well‐known global temperature time series from in situ stations is not significantly impacted by urban warming.
Enhanced sidereal diurnal variation of galactic cosmic rays observed by the two‐hemisphere network of surface level muon telescopes
Authors: Munakata K. , Kitawada T. , Yasue S. , Mori S. , Kato C. , Koyama M. , Akahane S. , Hall D. L. , Fujii Z. , Fujimoto K. , Humble J. E. , Fenton A. G. , Fenton K. B. , Duldig M. L.
Published: September 2002

Significant enhancements of the cosmic ray sidereal diurnal variation were observed during the period 1992–1995 by the two‐hemisphere network of surface‐level multidirectional muon telescopes at Hobart (Tasmania, Australia) and Nagoya (Aichi, Japan). The telescopes cover the primary cosmic ray rigidity range of 50–120 GV. Since the enhancement is less prominent in the higher rigidity range (150–550 GV) covered by the shallow underground observations at Misato and Sakashita, it is concluded that the enhancement was caused by significant solar modulation in the lower energy region. Observed sidereal diurnal variations, corrected for spurious variations by a procedure proposed by Nagashima, give a space harmonic vector with amplitude of 0.104 ± 0.008% at 60 GV and maximum at 6.9 ± 0.3 hour local sidereal time. The time of maximum is consistent with northward streaming of cosmic rays perpendicular to the ecliptic plane. Such a north–south anisotropy is expected from cross‐field ξNS = − λ⊥ Gθ diffusion if both the cross‐field mean‐free‐path λ⊥ and the southward directed unidirectional latitudinal density gradient Gθ have large enough magnitudes. It is shown that the sector‐dependent solar diurnal variations are also enhanced in the period, consistent with Gθ being directed south of the ecliptic plane. Magnitudes of Gθ and λ⊥ derived from the observations are discussed.
A study of omega bands and Ps6 pulsations on the ground, at low altitude and at geostationary orbit
Authors: Jorgensen A. M. , Spence H. E. , Hughes T. J. , McDiarmid D.
Published: September 2002

We investigate the electrodynamic coupling between auroral omega bands and the inner magnetosphere. The goal of this study is to determine the features to which omega bands map in the magnetosphere. To establish the auroral‐magnetosphere connection, we appeal to the case study analysis of the data rich event of September 26, 1989. At 6 magnetic local time (MLT), two trains of Ps6 pulsations (ground magnetic signatures of omega bands) were observed to drift over the Canadian Auroral Network For the OPEN Program Unified Study (CANOPUS) chain. At the same time periodic ionospheric flow patterns moved through the collocated Bistatic Auroral Radar System (BARS) field of view. Similar coincident magnetic variations were observed by GOES 6, GOES 7 and SCATHA, all of which had magnetic foot points near the CANOPUS/BARS stations. SCATHA, which was located at 6 MLT, 0.5 RE earthward of GOES 7 observed the 10 min period pulsations, whereas GOES 7 did not. In addition, DMSP F6 and F8 were over‐flying the region and observed characteristic precipitation and flow signatures. From this fortunate constellation of ground and space observations, we conclude that auroral omega bands are the electrodynamic signature of a corrugated current sheet (or some similar spatially localized magnetic structure) in the near‐Earth geostationary magnetosphere.
Magnetopause from pressure balance
Authors: Sotirelis Thomas , Meng Ching‐I.
Published: September 2002

The shape of the magnetopause and the field due to magnetopause currents are calculated from the requirement that the pressure in the magnetosheath be balanced by magnetic pressure inside the magnetosphere. The field due to magnetopause currents is calculated to be consistent with the iteratively adjusted magnetopause shape. The field due to current systems inside the magnetosphere is taken from the T96 model [Tsyganenko, 1996], which carries information from ∼47,000 magnetic field observations. Many different magnetospheric configurations were found for a variety of conditions. Changes in the shape of the magnetopause with varying dipole tilt angle stood out. The magnetotail and the nose (the point closest to the Sun) were found to shift vertically, in opposite directions, for nonzero dipole tilt. The vertical offset of the nose from the Earth‐Sun line varied linearly with dipole tilt angle, reaching ∼3 RE for maximal tilt and having a weak dependence on solar wind dynamic pressure. The formation of a secondary stagnation point just above the sunward cusp was indicated for absolute dipole tilts in excess of 15°. The magnitude of the field strength at its local maximum just behind the cusp was determined as a function of dipole tilt angle and the subsolar field strength. Calculated magnetopause shapes and observed magnetopause crossings were found to be consistent when the tilt angle was taken into account. Variations in the latitude of the magnetic cusps with dynamic pressure, interplanetary magnetic field Bz, and dipole tilt were reasonably consistent with observed variations in the latitude of the particle cusp.
GSWM‐98: Results for migrating solar tides
Authors: Hagan M. E. , Burrage M. D. , Forbes J. M. , Hackney J. , Randel W. J. , Zhang X.
Published: September 2002

We report on new global‐scale wave model (GSWM) predictions for the migrating solar tide in the troposphere, stratosphere, mesosphere and lower thermosphere. The model revision, hereafter GSWM‐98, includes an updated gravity wave (GW) stress parameterization and modifications to the background atmosphere based on 6‐year monthly averaged Upper Atmosphere Research Satellite (UARS) climatologies. UARS Halogen Occultation Experiment and Microwave Limb Sounder ozone data are used to define the strato‐mesospheric tidal source, while GSWM‐98 background winds are based on UARS High Resolution Doppler Interferometer (HRDI) zonal mean zonal wind data. We quantify and interpret differences between previous diurnal and semidiurnal predictions, hereafter GSWM‐95, and GSWM‐98 results. The revised GW stress parameterization accounts for the most profound changes and leads to seasonal variability predictions that are consistent with diurnal amplitudes observed in the upper mesosphere and lower thermosphere. Unresolved differences between HRDI and other wind climatologies significantly affect MLT tidal predictions.
Effects of suprathermal tails on auroral electrodynamics
Authors: Dors Eric E. , Kletzing Craig A.
Published: September 2002

The auroral current density‐voltage and energy flux density‐voltage relationships are derived under the assumption that magnetospheric electrons above the auroral acceleration region are described by the κ distribution function. To illustrate the effects of this boundary condition on auroral precipitation, a two‐dimensional model of auroral electrodynamics similar to that of Lyons [1980] has been developed by imposing current continuity in a region of converging electric field in the auroral zone. The current carried by precipitating magnetospheric electrons inside auroral arcs connects to return current regions at the arc edges via ionospheric Pedersen currents. A key feature is the ability to parameterize the magnetospheric boundary electron population as either a κ or Maxwellian distribution. For equal density and temperature a κ = 5 boundary condition yields a parallel potential drop ∼ 5% larger and a precipitating energy flux structure ∼ 5% wider than those of its Maxwellian counterpart. More significant differences emerge between these two distributions when the density is held constant but the spectral shape of the distributions are allowed to differ. The κ distribution results predict up to double the peak auroral energy flux and as much as a 20–30% increase in the latitudinal width of the auroral energy flux as compared with the Maxwellian results. The width and intensity of the inverted V structures in the model results are found to be closely related to the level of thermal energy flux outside the inverted V.
Quasi‐thermal noise in a drifting plasma: Theory and application to solar wind diagnostic on Ulysses
Authors: Issautier Karine , Meyer‐Vernet Nicole , Moncuquet Michel , Hoang Sang , McComas D. J.
Published: September 2002

The present paper provides the basic principles and analytic expressions of the quasi‐thermal noise spectroscopy extended to measure the plasma bulk speed, as a tool for in situ space plasma diagnostics. This method is based on the analysis of the electrostatic field spectrum produced by the quasi‐thermal fluctuations of the electrons and by the Dopplershifted thermal fluctuations of the ions; it requires a sensitive radio receiver connected to an electric wire dipole antenna. Neglecting the plasma bulk speed, the technique has been routinely used in the low‐speed solar wind, and it gives accurate measurements of the electron density and core temperature, in addition to estimates of parameters of the hot electron component. The present generalization of the method takes into account the plasma speed and thereby improves the thermal electron temperature diagnostic. The technique, which is relatively immune to spacecraft potential and photoelectron perturbations, is complementary to standard electrostatic analysers. Application to the radio receiver data from the Ulysses spacecraft yields an accurate plasma diagnostic. Comparisons of these results with those deduced from the particle analyser experiment on board Ulysses are presented and discussed.
Seismic velocity studies of a gas hydrate bottom‐simulating reflector on the northern Cascadia continental margin: Amplitude modeling and full waveform inversion
Authors: Yuan T. , Spence G. D. , Hyndman R. D. , Minshull T. A. , Singh S. C.
Published: September 2002

On the northern Cascadia subduction margin, the multichannel seismic amplitude‐versus‐offset (AVO) behavior of a bottom‐simulating reflector (BSR) suggests a P wave velocity change from high‐velocity hydrate‐bearing sediment to lower velocity sediment containing a small amount of free gas. The observed nonlinear AVO behavior, constant or slightly decreasing amplitudes at near‐to‐mid offsets and a large‐amplitude increase at far offsets, can be reproduced in the models if an S wave velocity enhancement is assumed as expected from hydrate cementation. The AVO behavior of the hydrate BSR is found not to be as useful as was earlier thought for determining the amount of free gas below the BSR. This is because Poisson's ratio change below the BSR due to gas is likely very small in high‐porosity unconsolidated sediments. The uncertainty in the models is large, as there is no reliable S wave velocity information for the sediments containing hydrate or gas. AVO modeling alone is not sufficient to distinguish different velocity models across the BSR. Our interpretation of the BSR amplitude behavior is that a P wave velocity increase above the BSR is the main cause of the BSR reflection amplitude increase at large incidence angles. Caution must be taken in applying AVO analysis, as little is known about S wave velocities. However, subtle differences in BSR amplitude behavior and reflection waveform can provide constraints through very careful full waveform inversion. A well‐defined reference velocity‐depth profile is also required to represent water‐saturated sediment unaffected by either hydrate or free gas. Using full waveform velocity inversion, a high‐resolution velocity model for the hydrate BSR has been derived. The best fit model for the seismic data near the Ocean Drilling Program (ODP) sites 889/890 consists of a high‐velocity zone above the BSR and a thin low‐velocity layer below, in agreement with the ODP downhole velocity data.
Strain changes for the 1987 Vatnafjöll earthquake in south Iceland and possible magmatic triggering
Authors: Ágústsson Kristján , Linde Alan T. , Stefánsson Ragnar , Sacks Selwyn
Published: September 2002

On May 25, 1987, at 11:31, a M = 5.8 earthquake occurred at the southern end of Vatnafjöll volcanic ridge in south Iceland. This is the largest event in the south Iceland lowland since a M = 7.0 earthquake in 1912 which was located approximately 15 km to the west of the Vatnafjöll earthquake. Vatnafjöll is located at the junction of the south Iceland seismic zone, a left lateral transform zone, and the eastern volcanic zone which is a zone of rifting and volcanism. In May and June 1987, several foreshocks and aftershocks were recorded on the local seismic network as well as the mainshock. A clear coseismic step associated with the mainshock was observed at all operating stations of a volumetric strainmeter network in southern Iceland. Steps associated with some foreshocks and aftershocks were also observed at the closest strain stations. Slow strain changes, before and after the mainshock, lasting a few days, were also observed. Forward modeling of the coseismic strainmeter signals of the mainshock suggests a double couple solution where the slip is mostly right lateral strike slip on a subvertical plane with a northerly strike. The solution has a good fit to observations and is in good agreement with interpretation of seismometer data. This solution indicates a stress field similar to that in the south Iceland seismic zone. The slow strain changes, which start about 10 min after the first foreshock, may indicate magma involvement in the process. Changes, associated with an intrusion and pressure release, may affect the strain field and possibly trigger the mainshock. The strainmeter records open up a new view of the seismic strain event as a combination of seismic strain release and a slower process of magma intrusion.
Submergence and uplift associated with the giant 1833 Sumatran subduction earthquake: Evidence from coral microatolls
Authors: Zachariasen Judith , Sieh Kerry , Taylor Frederick W. , Edwards R. Lawrence , Hantoro Wahyoe S.
Published: September 2002

The giant Sumatran subduction earthquake of 1833 appears as a large emergence event in fossil coral microatolls on the reefs of Sumatra's outer‐arc ridge. Stratigraphic analysis of these and living microatolls nearby allow us to estimate that 1833 emergence increased trenchward from about 1 to 2 m. This pattern and magnitude of uplift are consistent with about 13 m of slip on the subduction interface and suggest a magnitude (Mw) of 8.8–9.2 for the earthquake. The fossil microatolls also record rapid submergence in the decades prior to the earthquake, with rates increasing trenchward from 5 to 11 mm/yr. Living microatolls show similar rates and a similar pattern. The fossil microatolls also record at least two less extensive emergence events in the decades prior to 1833. These observations show that coral microatolls can be useful paleoseismic and paleogeodetic instruments in convergent tectonic environments.
Evolution of the Australian‐Antarctic discordance since Miocene time
Authors: Marks Karen M. , Stock Joann M. , Quinn Katherine J.
Published: September 2002

In this study we chronicle the development of the Australian‐Antarctic discordance (AAD), the crenelated portion of the Southeast Indian Ridge between ∼120° and 128°E, since anomaly 6y time (19 Ma). We reconstruct satellite‐derived marine gravity fields and depth anomalies at selected times by first removing anomalies overlying seafloor younger than the selected age, and then rotating the remaining anomalies through improved finite rotations based on a very detailed set of magnetic anomaly identifications. Our gravity field reconstructions reveal that the overall length of the Australian‐Antarctic plate boundary within the AAD has been increasing since 19 Ma. Concomitantly, the number of propagating rifts and fracture zones in the vicinity of the discordance has increased dramatically in recent times, effectively dividing it into its present‐day configuration of five distinct spreading corridors (B1‐B5) that are offset alternately to the north and south and exhibit varying degrees of asymmetric spreading. Our bathymetric reconstructions show that the regional, arcuate‐shaped, negative depth anomaly (deeper than predicted by normal lithospheric cooling models) presently centered on the discordance began migrating westward before anomaly 5ad time (∼14.4 Ma), and that a localized depth anomaly low, which at time 5ad lay on the ridge axis in spreading corridor B5, has been split apart by subsequent seafloor spreading. The magnetic anomaly patterns suggest that the depth anomaly is not always associated with a particularly contorted plate boundary geometry. Although the plate boundary within the AAD has been getting progressively more crenelated with time, this effect shows little to no migration along the ridge axis since 19 Ma. Thus any geodynamic models of the evolution of the discordance must account for the following observations: (1) the crenelation of the plate boundary within the AAD has increased with time, (2) the center of the crenelated zone does not appear to have migrated along the ridge crest, and (3) both the depth anomaly and the isotopic boundary between Pacific and Indian mantle have been migrating westward along the ridge axis but at apparently different rates. We suggest that both along‐axis migration of the depth anomaly and isotopic boundary, as well as temporal variation in the upwelling mantle material beneath the AAD, and local tectonic effects are required in order to explain these observations.
Three‐dimensional P and S wave velocity structures of the Coso Geothermal Area, California, from microseismic travel time data
Authors: Wu Huatao , Lees Jonathan M.
Published: September 2002

High precision P and S wave travel times for 2104 microearthquakes with focus <6 km are used in a non‐linear inversion to derive high‐resolution three‐dimensional compressional and shear velocity structures at the Coso Geothermal Area in eastern California. Block size for the inversion is 0.2 km horizontally and 0.5 km vertically and inversions are investigated in the upper 5 km of the geothermal area. Spatial resolution, calculated by synthetic modeling of a cross model at critical locations, is estimated to be 0.35 km for Vp and 0.5 km for Vs. Model uncertainties are estimated by a jackknife approach and simulation of random and associated picking errors. Low‐velocity zones for both P and S waves are identified at geothermal production depths (1–3 km). A large, low Vp (−6%) zone is found at depth 2–2.5 km 2 km southwest of Sugarloaf Mountain where high attenuation has been previously reported. However, a general high‐ Vp zone is seen under Coso Hot Springs with a slightly low Vs zone, which is characteristic of fluid saturation. The overall distributions of Vp and Vs perturbations do not correlate. An isolated high‐ Vs (+9%) feature, about 2 km in diameter, is unambiguously seen 2 km due west of Sugarloaf extending from surface to depth. This feature is surrounded by a circular, low‐ Vs belt of ∼1 km width. The surrounding belt is probably the cracked, high‐porosity reservoir/conduit of geothermal fluid flow. In the 2 km southwest Sugarloaf region, we found low Vp and high Vs at geothermal production depths from 1 to 2.5 km. Combined with attenuation results, this may represent a hot, fluid‐depleted center of magmatic activity.
Sensitivity of the tropical Pacific Ocean simulation to the temporal and spatial resolution of wind forcing
Authors: Chen Dake , Liu W. Timothy , Zebiak Stephen E. , Cane Mark A. , Kushnir Yochanan , Witter Donna
Published: September 2002

The effects of temporal and spatial smoothing of wind forcing were evaluated in a model simulation of the tropical Pacific Ocean variability during the onset phase of the 1997/1998 El Niño. A total of 16 experiments were performed using the NASA scatterometer wind data smoothed at time intervals from 1 to 30 days and on spatial scales from 1° to 10°. A major effect of the temporal smoothing of winds is to warm sea surface temperature (SST) by reducing the energy input for vertical turbulent mixing. When the daily wind forcing was replaced by the monthly average, the mean SST increased by 0.5° to 1° over most of the tropical Pacific. The spatial smoothing of winds is not as effective as the temporal smoothing in causing SST warming, but it has a more severe influence on dynamical ocean response for smoothing scales above 5°. The onset of the 1997/1998 El Niño can be successfully simulated using the wind forcing averaged to monthly intervals and 2° squares. For climate models the spatial smoothing of wind forcing on scales larger than the width of the equatorial waveguide is a more serious limitation than the temporal smoothing on scales up to 1 month.
High‐frequency internal waves on a sloping shelf
Authors: Pringle James M. , Brink Kenneth H.
Published: September 2002

The behavior of an internal wave in a continuously stratified fluid over a sloping bottom is examined by finding approximate analytic solutions for the amplitude of waves in a coastal ocean with constant bottom slope, linear bottom friction, and barotropic mean flows. These solutions are valid for frequencies higher than the frequency of critical reflection from the sloping bottom. The solutions show that internal waves propagating toward the shore are refracted, so that their crests become parallel to shore as they approach the coast, and outward propagating waves are reflected back toward the coast from a caustic. Inviscid solutions predict that the amplitude of a wave goes to infinity at the coast, but these infinite amplitudes are removed by even infinitesimal bottom friction. These solutions for individual rays are then integrated for an ensemble of internal wave rays of random orientation that originate at the shelf break and propagate across the shelf. It is found that for much of the shelf the shape of the current ellipse caused by these waves is nearly independent of the waves' frequency. The orientation of the current ellipse relative to isobaths is controlled by the redness of the internal wave spectrum at the shelf break and the strength of mean currents. Friction is more important on broader shelves, and consequently, on broad shelves the internal wave climate is likely to be dominated by any internal waves generated on the shelf, not waves propagating in from the deep ocean.
Simulation of carbon‐nitrogen cycling during spring upwelling in the Cariaco Basin
Authors: Walsh J. J. , Dieterle Dwight A. , Müller‐Karger Frank E. , Bohrer Richard , Bissett W. Paul , Varela Ramón J. , Aparicio Ruben , Díaz Rafael , Thunell Robert , Taylor Gordon T. , Scranton Mary I. , Fanning Kent A. , Peltzer Edward T.
Published: September 2002

Coupled biological‐physical models of carbon‐nitrogen cycling by phytoplankton, zooplankton, and bacteria assess the impacts of nitrogen fixation and upwelled nitrate during new production within the shelf environs of the Cariaco Basin. During spring upwelling in response to a mean wind forcing of 8 m s−1, the physical model matches remote‐sensing and hydrographic estimates of surface temperature. Within the three‐dimensional flow field, the steady solutions of the biological model of a simple food web of diatoms, adult calanoid copepods, and ammonifying/nitrifying bacteria approximate within ∼9% the mean spring observations of settling fluxes caught by a sediment trap at ∼240 m, moored at our time series site in the basin. The models also estimate within ∼11% the average 14C net primary production and mimic the sparse observations of the spatial fields of nitrate and light penetration during the same time period of February‐April. Stocks of colored dissolved organic matter are evidently small and diazotrophy is minimal during spring. In one summer case of the model with weaker wind forcing, however, the simulated net primary production is 14% of that measured in August‐September, while the predicted detrital flux is then 30% of the observed. Addition of a cyanophyte state variable, with another source of new nitrogen, would remedy the seasonal deficiencies of the biological model, attributed to use of a single phytoplankton group.
Molecular distributions of water soluble dicarboxylic acids in marine aerosols over the Pacific Ocean including tropics
Authors: Kawamura Kimitaka , Sakaguchi Futoshi
Published: September 2002

Remote marine aerosols collected over the western North to equatorial Pacific (34°N–14°S, 140°E‐150°W) were studied for low molecular weight dicarboxylic acids using a capillary gas chromatography (GC) and GC/mass spectrometer, and for total carbon and nitrogen contents. Homologous series of dicarboxylic acids (C2–C10) including keto‐ and hydroxy‐dicarboxylic acids were detected in the samples with a concentration range of 10–250 ng m−3 (average 63 ng m−3 and median 44 ng m−3). Their molecular distributions showed a predominance of oxalic acid (C2), followed by malonic acid (C3). The smallest diacid (C2, 6.5–161 ng m−3 with average 40 ng m−3 and median 17 ng m−3) composed 45–75% (average 65%) of the total diacids. The diacids showed higher concentrations in the western Pacific rim near Japanese islands and showed lower concentrations in the central and tropical Pacific. However, relative abundances of the diacid‐carbon in the total aerosol carbon (1.1–15.8%) were found to be higher in the equatorial central Pacific. These diacids are probably in situ produced in the Pacific atmosphere by photochemical oxidation of gaseous and particulate precursors. Results of principal component analysis of individual diacid, coupled with an information on photochemical reactions, further support that C2 and C3 diacids are likely produced by the oxidation of C4 and longer‐chain diacids, whereas longer‐chain (C5–C10) diacids are produced through the oxidation of semivolatile fatty acids which are also oxidation products of unsaturated fatty acids. Concentrations of total C (0.069–5.27 μg m−3 with average 0.39 μg m−3 and median 0.15 μg m−3) and total N (0.026–1.44 μg m−3 with average 0.12 μg m−3 and median 0.077 μg m−3) were generally higher over the western Pacific.
Isentropic, diabatic, and sedimentary transport of Mount Pinatubo aerosol
Authors: Rogers H. L. , Norton W. A. , Lambert A. , Grainger R. G.
Published: September 2002

Observations of Mount Pinatubo aerosol as measured by the ISAMS instrument on UARS are presented for December 1991. These observations show a tropical reservoir of high aerosol with steep gradients across the subtropics. On the 450 K isentrope there is a ring of high aerosol in midlatitudes which is separated from the tropical reservoir by an approximately zonal band of lower aerosol values. The ISAMS aerosol data are compared with output from the off‐line three‐dimensional transport model SLIMCAT. Integrations are performed with isentropic transport only, diabatic transport only, isentropic and diabatic transport, and isentropic, diabatic and sedimentary transport of aerosol. Integrations using winds and temperatures from UKMO and ECMWF are compared. It is shown that even in the lower stratosphere, cross‐isentropic transport over the timescale of a month can have a significant effect on the distribution of aerosol. The SLIMCAT integrations with isentropic transport only do not form a ring of high aerosol in midlatitudes on the 450 K isentrope. Inclusion of diabatic transport in the SLIMCAT integration shows that this ring forms from diabatic descent of air containing higher aerosol concentrations from aloft. Isentropic transport of high‐aerosol air from the tropics into midlatitudes on the 500 K isentrope, followed by diabatic descent, further increases the values in the midlatitude ring on the 450 K isentrope. Inclusion of the sedimentation of aerosol in SLIMCAT integrations significantly offsets the diabatic ascent in the tropics. The SLIMCAT integrations, particularly those run using UKMO analyses, produce too much transport of midlatitude air into the tropics. The implications for accurate modeling of the tropical reservoir are discussed.
Aircraft observations and modeling of sky radiance distributions from aerosol during TARFOX
Authors: Francis Peter N. , Hignett Phillip , Taylor Jonathan P.
Published: September 2002

We present data from three cases studied during TARFOX, the Tropospheric Aerosol Radiative Forcing Observational Experiment. Aircraft measurements of the aerosol chemical composition, size distribution, and hygroscopic growth are used to construct a detailed picture of the aerosol microphysical characteristics. The distribution of the sky radiance field is then calculated at several wavelengths in the visible and near‐infrared region of the spectrum from these data. The simulations are compared with observed radiance distributions made from one of the aircraft. Reasonable agreement is obtained for two of the cases considered, but significant differences exist for the third, which we are unable to explain at the present time.
Two‐ and four‐stream optical properties for water clouds and solar wavelengths
Authors: Dobbie J. Steven , Li Jiangnan , Chýlek Petr
Published: September 2002

Presented is a parameterization of the liquid water droplet optical properties for the solar spectrum. Two models are provided: a 4‐band model for use in general circulation models and a 31‐band model for use in higher spectral resolution investigations. The form of the parameterization is a simple extension of Slingo [1989], and the subdivision of wavelengths into bands is almost identical. The parameterization scheme is for all of the optical properties needed to perform 2‐ and 4‐stream calculations. The 4‐band model has the same spectral divisions as Slingo [1989], whereas the 31‐band model has finer resolution of the absorbing bands in the near infrared. The parameterized single‐scattering optical properties are accurate to within 0.5% compared to exact Mie calculations for both band models over the reff range from 5 to 40 μm. The layer radiative properties, from both two‐ and four‐stream methods, are almost always within 1% accuracy compared to calculations using exact optical properties as inputs. Also, it is shown that using the Henyey‐Greenstein phase function to obtain the higher‐order moments, used in four‐stream calculations, results in substantial error in the layer radiative properties compared to using exact Mie inputs.
Absorption of solar radiation by the cloudy atmosphere: Further interpretations of collocated aircraft measurements
Authors: Cess Robert D. , Zhang Minghua , Valero Francisco P. J. , Pope Shelly K. , Bucholtz Anthony , Bush Brett , Zender Charles S. , Vitko John
Published: September 2002

We have extended the interpretations made in two prior studies of the aircraft shortwave radiation measurements that were obtained as part of the Atmospheric Radiation Measurements (ARM) Enhanced Shortwave Experiment (ARESE). These extended interpretations use the 500 nm (10 nm bandwidth) measurements to minimize sampling errors in the broadband measurements. It is indicated that the clouds present during this experiment absorb more shortwave radiation than predicted by clear skies and thus by theoretical models, that at least some (≤20%) of this enhanced cloud absorption occurs at wavelengths <680 nm, and that the observed cloud absorption does not appear to be an artifact of sampling errors nor of instrument calibration errors.
First geometrical path length probability density function derivation of the skylight from high‐resolution oxygen A‐band spectroscopy: 2. Derivation of the Lévy index for the skylight transmitted by midlatitude clouds
Authors: Pfeilsticker K.
Published: September 2002

For the first time Lévy indices (γ) of the solar light transmitted by cloudy skies at mid latitude (50°N, 8.2°E) are reported. The Lévy index describes the dependence of the mean geometrical paths (< LT > ) of photons transmitted from cloudy skies as a function of the vertical cloud extension (Hc) expressed by the scaling law  ∼ Hcγ. For a set of 33 individual cloudy sky < LT > measurements, reported cloud types and heights, Lévy indices are deduced. It is found that the inferred Lévy indices cluster into the range of 1 ≤ γ ≤ 2 for “all sky” observations, and into a range 1.5 ≤ γ ≤ 2 for optically very thick clouds. The observations provide evidence that the cloudy sky geometrical path lengths are Lévy distributed with the γ value depending on the cloud morphology (the shape of individual clouds and the spatial arrangement of the clouds) but also on the internal cloud inhomogeneities. Because of a particular sensitivity of our method to detect the radiative transfer (RT) caused by clouds (rather than by the clear sky parts of the atmosphere), the inferred type of the path statistics is expected to reflect mostly the path length distribution caused by cloud inhomogeneities rather than by the cloud morphology. Since the cloud inhomogeneities are caused by dynamic processes (besides other factors), the RT transfer is expected to be closely connected to atmospheric dynamics. From this it is concluded that the absorption of solar radiation in cloudy skies is connected to the dynamic state (whether it is stratified or convective) of the cloud cover. In particular, it is expected to be different (mostly larger) than calculated by naively assuming homogeneous horizontally infinite cloud covers in conventional non statistical RT models.
Radio atmospheric propagation on Mars and potential remote sensing applications
Authors: Cummer Steven A. , Farrell William M.
Published: September 2002

We theoretically analyze the propagation of very low frequency (VLF) and extremely low frequency (ELF) electromagnetic energy in the spherical waveguide formed by the ground and ionosphere of Mars to investigate the possibility of using such signals to remotely sense Martian ground conductivity and ionospheric parameters. This energy is presumed to be radiated from an electrical discharge in a Martian dust storm. Using a synthesis of observed and modeled Martian ionospheric and ground parameters and assuming a discharge current similar to that in a terrestrial lightning discharge, we calculate radio atmospheric spectra and waveforms for a variety of discharge orientations and observed electromagnetic field components. A number of characteristics of the modeled Martian radio atmospherics (sferics) are found to be significantly different from those of terrestrial sferics, and we discuss how these features could provide information regarding the Martian ionosphere. We also show that measurements of VLF and ELF attenuation rates could provide a measurement of large‐scale ground conductivity to a depth of a few kilometers or more, thereby providing a technique for probing large‐scale subsurface geological features which affect bulk conductivity, such as areas containing ice or water.
Gruithuisen domes region: A candidate for an extended nonmare volcanism unit on the Moon
Authors: Chevrel Serge D. , Pinet Patrick C. , Head James W.
Published: September 2002

Small lunar areas known as red spots are thought to represent good candidates for nonmare volcanic units predating or contemporaneous with the period of mare volcanism. In this study, we present imaging telescopic and orbital Clementine multispectral surveys of the Gruithuisen region, located in the northwestern border of Mare Imbrium, which contains Imbrian age domical features of likely viscous volcanic origin with spectral characteristics of red spot areas. A rather spectrally homogeneous unit having typical characteristics of red spots is found to coincide with the material within the morphological boundaries of the Gruithuisen Delta, Gamma and Northwest domes. An extended “dome‐like” unit is identified spectrally and surrounds and extends to the west and the north of the domes. This unit shows spectral characteristics close to those of the domes, suggesting the presence of a significant amount of dome material extending many kilometers away from the domes themselves. Both the spectral characteristics of the dome and the dome‐like unit are clearly different from those of highlands and the surrounding mare basalts. The spectral identification of a widespread dome‐like unit suggests that the specific style of eruption that is inferred for the formation of the domes (i.e., viscous flows of possible more silicic composition) might have occurred on a regional scale in this part of the Moon, prior to the Iridum event about 3.8 Gyr ago. This volcanic style appears to be more widespread in the early part of lunar history than previously thought.