bluuebunny/crossref_metadata_2025 huggingface dataset:
Trail in the atmosphere of the 29 December 2000 meteor as recorded in Tahiti: Characteristics and trajectory reconstitution
Authors: Le Pichon A. , Guérin J. M. , Blanc E. , Reymond D.
Published: December 2002

On 29 December 2000, a meteor entry in the atmosphere produced several bright lights in the sky of Tahiti and intense sonic booms around midnight local time. This event was detected by the Laboratoire de Détection et de Géophysique French Polynesian seismic network and by the IS24 infrasound station in Tahiti operating for the Comprehensive Test Ban Treaty Organization (CTBTO). Both seismic and infrasonic signals indicated that the altitude of the meteor's last explosion was ∼45 km. From the wave azimuth and incidence angle determined through infrasonic data processing, the meteor trajectory has been backtracked over 55 km. Determination of the azimuth and incidence angle of the infrasonic arrivals permitted the determination of a 55 km segment of the meteor trajectory. The velocity of the meteor decreased from 17 to 15 km/s in ∼4 s, while its altitude changed from 55 to 45 km. The diameter and the kinetic energy of the bolide are evaluated using the infrasonic measurements and numerical simulations.
A discussion of upper stratospheric ozone asymmetries and SAGE trends
Authors: Li Jinlong , Cunnold Derek M. , Wang Hsiang‐Jui , Yang Eun‐Su , Newchurch Michael J.
Published: December 2002

A chemical box model constrained by Upper Atmosphere Research Satellite (UARS) measurements of CH4, H2O, NOx, and temperature in 1992–1994 has been used in an attempt to simulate ozone trend measurements from the Stratospheric Aerosol and Gas Experiment (SAGE) at 43 km, 45° latitude and their hemispheric differences. The model is successful in simulating the seasonal cycle in ozone mixing ratios observed by the Microwave Limb Sounder (MLS) and the Solar Backscattered Ultraviolet (SBUV) instrument including the 15% larger values in the Southern Hemisphere at the wintertime ozone maximum. The model indicates that this hemispheric asymmetry is associated with hemispheric temperature differences of approximately 10°K; in contrast, hemispheric differences in methane and the resulting effects on ClOx make only a small contribution to this ozone asymmetry. The model predicts that, based on observed Cly increases, the ozone decrease in the Southern Hemisphere should have exceeded that in the Northern Hemisphere by approximately 1%/decade. This is consistent with an observed ozone hemispheric trend difference of 1.7 ± 2.1%/decade (1σ) for 1979–1997 and −0.8 ± 2.8%/decade for 1985–1997 from SAGE I and SAGE II (version 6.1) measurements. These trend differences are caused by hemispheric differences in temperature in early winter and in CH4 in late winter. The model, based on changes in Cly but not in other specified parameters, calculates a larger downtrend of ozone than is observed by SAGE II in 1985–1997 by approximately 3.1 ± 1.4%/decade (1σ), but it qualitatively simulates the observed ozone trend variations over the period 1979–1997. The amplitude of the model calculated downtrend would be reduced by approximately 1%/decade for a methane increase of 1%/yr. Observed temperature decreases of approximately 0.1°K/yr would have decreased the magnitudes of the calculated ozone downtrends on pressure surfaces by approximately 1%/decade but could have affected SAGE trends by a small amount in the opposite direction because of associated geopotential height changes.
Seasonal cycles of ozone and oxidized nitrogen species in northeast Asia 2. A model analysis of the roles of chemistry and transport
Authors: Tanimoto Hiroshi , Wild Oliver , Kato Shungo , Furutani Hiroshi , Makide Yoshihiro , Komazaki Yuichi , Hashimoto Shigeru , Tanaka Shigeru , Akimoto Hajime
Published: December 2002

The dominant factors controlling the seasonal variations of ozone (O3) and three major oxidized nitrogen species, peroxyacetyl nitrate (PAN), nitrogen oxides (NOx), and nitric acid (HNO3), in northeast Asia are investigated by using a three‐dimensional global chemical transport model to analyze surface observations made at Rishiri Island, a remote island in northern Japan. The model was evaluated by comparing with observed seasonal variations, and with the relationships between O3, CO, and PAN. We show that the model reproduces the chemical environment at Rishiri Island reasonably well, and that the seasonal cycles of O3, CO, NOy species, and VOCs are well predicted. The impact of local emissions on some of these constituents is significant, but is not the dominant factor affecting the seasonal cycles. The seasonal roles of chemistry and transport in controlling O3 and PAN are revealed by examining production/destruction and import/export/deposition fluxes in the boundary layer over the Rishiri region. For O3, transport plays a key role throughout the year, and the regional photochemical contribution is at most 10% in summer. For PAN, in contrast, transport dominates in winter, while in‐situ chemistry contributes as much as 75% in summer. It is suggested that the relative contribution of transport and in‐situ chemistry is significantly different for O3 and PAN, but that the wintertime dominance of transport due to the long chemical lifetimes of these species is sufficient to drive the seasonal cycles of springtime maximum and summertime minimum characteristic of remote sites.
The impact of observational weighting on the assimilation of GPS/MET bending angle
Authors: Shao H. , Zou X.
Published: December 2002

The sensitivity of Global Positioning System (GPS)/Meteorology (GPS/MET) bending angle assimilation to the specification of observational weightings is studied. Three weighings are used. The first is estimated based on background and observation differences. The second comes from a theoretical estimation of the errors in the calculation of radio occultation (RO) bending angles [Zou et al., 2002]. The third is given by Palmer et al. [2000]. A total of 52 single GPS/MET occultation experiments are carried out for each of these weightings. The relationships between the adjustment of the refractivity and the adjustments of the temperature, specific humidity, and surface pressure have been examined. Collocated radiosonde observations are used as independent data sources for the numerical evaluation of GPS/MET data assimilation results. The analysis increments of the specific humidity and the surface pressure have the same sign as that of the refractivity. The larger the analysis increments of the refractivity, the larger the analysis increments of the specific humidity and the surface pressure. Such a one‐to‐one correspondence is not found between the analysis increment of the temperature and the increment of the refractivity. The GPS/MET bending angle assimilation with these three weightings all provide reasonable improvements to the temperature and specific humidity analyses compared with radiosonde data. The National Centers for Environmental Prediction (NCEP) background fields are wetter than radiosonde measurements between 800 and 450 hPa. This positive bias of the background specific humidity is largely removed after the GPS/MET data assimilation with all three weightings. However, it is found that GPS/MET bending angle assimilation slightly increased the difference between the surface pressure analysis and the radiosonde observations. Different analysis variables have different sensitivities to the weightings. Among them, the sensitivities of the temperature and the surface pressure are most significant. In a further analysis, the sensitivities of the data assimilation to the variation of the gravity and the vertical resolution of the assimilated data are presented. The sensitivity to the gravity is not very significant. However, the increase of the vertical resolution of the assimilated bending angle observations produces more accurate refractivity and temperature analyses, with little impact on surface pressure fields. Moreover, the inconsistency between two independent observations may cause the background fields to be positively biased from one type of observation but negatively biased from the other type of observation. Such an inconsistency has been seen to affect the evaluation of the GPS/MET bending angle assimilation results using radiosonde observations.
On the features of clouds occurring over the Mackenzie River basin
Authors: Stewart Ronald E. , Burford Jason E.
Published: December 2002

To better characterize the occurrence of clouds and some of their features over the Mackenzie basin of northwestern Canada, surface‐based measurements of cloud fields have been examined from several operational observing sites. This article focuses on the determination of cloud cover fraction, cloud base height, multiple layering, and cloud type as well as the variations of these on temporal scales ranging from diurnal to interannual. In addition, the cloud features were related to the large‐scale circulation, large‐scale convergence, air mass, and surface temperature. The results indicate that clouds over this region are very common (occurring about 80% of the time and covering an average of about 60% of the sky), are linked with surface temperature variations (such as being less common and higher during winter cold periods), are poorly correlated with large‐scale factors (such as El Niño), and may be exhibiting some long‐term trends (such as an increase in cloud cover fraction).
Bright and dark regions on Mars: Particle size and mineralogical characteristics based on Thermal Emission Spectrometer data
Authors: Ruff Steven W. , Christensen Philip R.
Published: December 2002

Emissivity spectra (1670–200 cm−1) from the Mars Global Surveyor Thermal Emission Spectrometer (MGS‐TES) show significant differences between bright and dark surfaces, allowing further investigation of their physical and mineralogical character. TES spectra from bright surfaces (albedo ≥0.2) typically show lower emissivity at high wavenumbers (>1300 cm−1) than that of dark surfaces (albedo <0.2). The opposite behavior is evident in the low wavenumbers (<560 cm−1), where bright surfaces have higher emissivity than dark ones. These trends are consistent with the spectral behavior of silicate materials of varying particle size. The short wavelength feature displayed by TES spectra of bright surfaces is a relatively strong absorption that likely is the result of particle size effects of surface silicate particles ≪100 μm in size. A dust cover index (DCI) is developed that exploits this short wavelength feature, serving to identify surfaces that range from dust‐covered to dust‐free. As a gauge of surface‐obscuring silicate dust that can impact spectral measurements, the DCI is more direct than thermal inertia or albedo measurements. Spectral ratio analysis using emissivity spectra from adjacent bright and dark surfaces is explored as a means of deriving the mineralogy of surface dust. The result shows that the dust is dominated by silicate minerals with indication of a significant plagioclase feldspar component.
Evidence for platy hematite grains in Sinus Meridiani, Mars
Authors: Lane Melissa D. , Morris Richard V. , Mertzman Stanley A. , Christensen Philip R.
Published: December 2002

Midinfrared (∼1600–200 cm−1) spectral data received from the Mars Global Surveyor Thermal Emission Spectrometer (MGS TES) have provided evidence for a large hematite‐bearing (α‐Fe2O3) deposit in Sinus Meridiani, Mars. We report here the results of a laboratory spectroscopic investigation of 24 hematite samples, including polycrystalline hand samples (massive and schistose textures), single‐crystal hand samples, and particle‐size fractions (single‐crystal and polycrystalline discrete particles). Laboratory midinfrared analyses of crystallographically oriented hematite samples suggest that the hematite emission in Sinus Meridiani (SM) is predominantly from the crystallographic c‐face of hematite. This observation implies the presence of platy hematite particles, with the plate face being the crystallographic c‐face. The observations are consistent with a formational model where the platy, gray hematite originated as an iron‐oxide, chemically precipitated from Fe‐rich aqueous and/or hydrothermal solutions on early Mars, that was buried, recrystallized to platy hematite, and subsequently reexposed as lenses of schistose hematite in a friable, consolidated stratigraphic unit. Unconsolidated platy hematite particles are also likely to be present as a physical‐weathering product of the schistose hematite lenses.
Postwall waveguide slot array with cosecant radiation pattern and null filling for base station antennas in local multidistributed systems
Authors: Hirokawa J. , Yamazaki C. , Ando M.
Published: December 2002

The authors propose to use planar antennas of waveguide slots with the simple structure of postwall waveguide for base station antennas in Local Multipoint Distribution Systems (LMDS). The array has a cosecant radiation pattern with null filling in the vertical plane for uniform illumination in a sector area. The slots are paired as an element to achieve traveling wave excitation because the phase, as well as the amplitude, has to be controlled for null filling in a cosecant pattern. It is the first time to design an array of reflection‐canceling slot pairs to get a tapered distribution both in amplitude and phase. This paper extends the designability of the reflection‐canceling slot arrays. A 16‐element array is designed at 25–26 GHz band. The model array has a cosecant pattern with 3‐dB deviations and a peak gain of 17.1 dBi in measurements.
Some results extracted from the time domain version of the optical theorem
Authors: Karlsson Anders
Published: December 2002

The time domain version of the optical theorem is discussed. The theorem is derived from the optical theorem in the frequency domain by the Parseval's relation. It expresses the sum of the scattered and absorbed energies in terms of the scattered farfield in the forward direction. From the theorem, causality, and reciprocity, a number of results concerning the scattered and absorbed energies from a plane pulse that is scattered from bounded objects are obtained. Some of these results are verified by numerical calculations.
Oblique collision in the northeastern Caribbean from GPS measurements and geological observations
Authors: Mann Paul , Calais Eric , Ruegg Jean‐Claude , DeMets Charles , Jansma Pamela E. , Mattioli Glen S.
Published: December 2002

Previous Caribbean GPS studies have shown that the rigid interior of the Caribbean plate is moving east‐northeastward (070°) at a rate of 18–20 ± 3 mm/yr relative to North America. This direction implies maximum oblique convergence between the island of Hispaniola on the Caribbean plate and the 22–27‐km‐thick crust of the Bahama carbonate platform on the adjacent North America plate. We present a tectonic interpretation of a 15‐site GPS network which spans the Hispaniola‐Bahama oblique collision zone and includes stable plate interior sites on both the North America and Caribbean plates. Measurements span the time period of 1994–1999. In a North America reference frame, GPS velocities in Puerto Rico, St. Croix, and the Lesser Antilles indicate that these areas move as a single block in an east‐northeast direction (070°) at a rate of 19–20 mm/yr consistent with the movement of the rigid interior of the Caribbean plate. GPS velocities at six sites in central and eastern Hispaniola (Dominican Republic) show drastically different behavior with more eastwardly strikes (080°) and much slower rates (4–17 mm/yr) than areas of the stable Caribbean plate. The boundary between the relatively slower‐moving Hispaniola collisional zone and the relatively faster‐moving, uncollided Puerto Rico‐Virgin Islands area is the Mona Passage where late Neogene rifting occurs in a broad zone. Elastic modeling favors strain partitioning with oblique slip on the outer, low‐angle submarine thrust faults (North Hispaniola, Muertos) and strike slip on the inner, subvertical subaerial, strike‐slip faults (Septentrional, Enriquillo).
Natural and management influences on freshwater inflows and salinity in the San Francisco Estuary at monthly to interannual scales
Authors: Knowles Noah
Published: December 2002

Understanding the processes controlling the physics, chemistry, and biology of the San Francisco Estuary and their relation to climate variability is complicated by the combined influence on freshwater inflows of natural variability and upstream management. To distinguish these influences, alterations of estuarine inflow due to major reservoirs and freshwater pumping in the watershed were inferred from available data. Effects on salinity were estimated by using reconstructed estuarine inflows corresponding to differing levels of impairment to drive a numerical salinity model. Both natural and management inflow and salinity signals show strong interannual variability. Management effects raise salinities during the wet season, with maximum influence in spring. While year‐to‐year variations in all signals are very large, natural interannual variability can greatly exceed the range of management effects on salinity in the estuary.
What does a slug test measure: An investigation of instrument response and the effects of heterogeneity
Authors: Beckie Roger , Harvey Charles F.
Published: December 2002

We consider parameters determined by the inversion of slug‐test head recovery data with the homogeneous‐parameter model of Cooper et al. [1967] to be weighted spatial averages of transmissivity and storage defined at a smaller scale. We quantify the spatial averaging using a power‐average spatial filter expression. We determine the form of the filter function and the power exponent using numerically simulated slug‐test data. The filter function that describes how smaller‐scale transmissivity is weighted by slug tests displays an approximate 1/r2 behavior, with r the radial distance from the well. The radius of the cylinderical volume that is averaged by the slug test is inversely proportional to the square root of the storage coefficient (larger averaging volume with smaller storage). The power exponent grows from −0.19 to 0.345 as the ratio of the characteristic scale of the heterogeneity to the characteristic scale of the averaging volume grows, although a power exponent of zero, corresponding to geometric averaging, provides good results for most simulations. Our results show that while slug tests are useful to estimate transmissivity, they have dubious value for estimating storage coefficients. We find that the transmissivity estimate is unbiased and does not appear to be strongly influenced by storage properties. The storage coefficient estimate is, however, strongly influenced by the transmissivity and is biased. We investigate the interaction between storage coefficient and transmissivity by examining an analytical slug‐test model that contains two annular zones, each with distinct transmissivity and storage coefficient.
Transfer function‐noise modeling in continuous time using predefined impulse response functions
Authors: von Asmuth Jos R. , Bierkens Marc F. P. , Maas Kees
Published: December 2002

A method of transfer function‐noise (TFN) modeling is presented that operates in continuous time and uses a predefined family of impulse response (IR) functions. The resulting class of models is referred to as predefined IR function in continuous time (PIRFICT). It provides a useful tool for standardized analysis of time series, as it can be calibrated using irregularly spaced data and does not require a model identification phase prior to calibration. In section 2, the discrete Box‐Jenkins (BJ) model is presented and transformed into continuous time to obtain the PIRFICT model. The discrete transfer function of a BJ model, which is made up of a variable number of parameters, is replaced by a simple analytical expression that defines the IR function. From the IR function, block response functions are derived that enable the model to handle irregularly spaced data. In the example application, the parameter estimates and performance of the BJ and PIRFICT model are compared using a data set of 15 piezometers and a simulated series. It was found that the estimated transfer and BR functions of both models follow the same general pattern, although the BJ transfer functions are partly irregular. The performance of both models proves to be highly comparable for all piezometers.
Experiments and modeling of head cut migration in stratified soils
Authors: Stein Otto R. , LaTray Dean A.
Published: December 2002

A two‐dimensional model is developed to predict head cut migration rate for the specific case of a relatively erosion‐resistant soil layer overlying a deep, relatively erosive base soil. For this geometry, head cut migration can occur as a series of discrete mass failures of the surface layer caused by undercutting in a plunge pool formed immediately downstream. The length scale of one failure episode is modeled as a cantilevered slab failing in bending. The timescale for each failure episode is controlled by the rate and geometry of base layer scour, which is modeled independently of cantilevered slab properties. An integration of the two model components for the case of steady flow and uniform soil properties predicts linear upstream head cut migration with time, occurring in discrete steps bounded by successive mass failure events. The model is calibrated and tested in a series of flume experiments representing ideal conditions of different initial geometries and flow conditions. Head cut migration occurred by the proposed mechanism in a nearly linear rate. Average error between the observed and predicted retreat rate is 40%, most of this error is attributable to prediction of the scour hole shape.
Infiltration during soil sealing: The effect of areal heterogeneity of soil hydraulic properties
Authors: Assouline S. , Mualem Y.
Published: December 2002

The combined effects of soil surface sealing and areal heterogeneity of the soil hydraulic properties on the mean infiltration curve are studied here for the first time. Seal formation during rainfall is simulated according to the dynamic model of Assouline and Mualem [1997]. Areal heterogeneity is represented by lognormal distribution of the saturated hydraulic conductivity of the initially undisturbed soil and by related distributions of the other soil parameters. The mean infiltration curve of the heterogeneous field is evaluated presuming that horizontal fluxes are negligible. It is found that when soil surface sealing is taken into account in a heterogeneous field, the ponding time is only slightly affected. However, significantly more runoff is produced compared to nonsealing field (mulched), with the relative area contributing to surface runoff being increased from 65 to 95%. The relative effect of field heterogeneity on the infiltration curve increases for higher rainfall intensity. The formation of soil surface seal apparently reduces the effect of the field areal variability on the steady infiltration rate. The infiltration rate after 60 min of rainfall distributes lognormally under sealing conditions, while it distributes normally in the case of the unsealed soil. The final infiltration rate resulting from the assumption of a sealed uniform field is underestimated compared to sealed heterogeneous field, with the relative effect being larger for a loam soil (−51%) than for a sandy loam soil (−26%). Also, the approximation that the infiltration curve is a unique function of cumulative rainfall independent of rainfall intensity is not valid in a sealing heterogeneous field, and its application in such a case would be more erroneous than in uniform fields. On the other hand, one may disregard the variability of all soil parameters, except the hydraulic conductivity, when calculating infiltration.
Numerical modeling: A complementary tool for studying CO2 emissions from hydroelectric reservoirs
Authors: Barrette Nathalie , Laprise Rene
Published: December 2002

In 1993, a vast study began on the production and emission of CO2 from hydroelectric reservoirs in central northern Québec. During the sampling field trips, information was collected about water temperature profiles, CO2 surface atmospheric concentrations, dissolved CO2 concentration profiles through the depth of the reservoirs, and CO2 fluxes at the surface and the bottom of the reservoirs, as well as many surface meteorological parameters. One of the goals of the project was to develop a mathematical model capable of simulating the physical processes responsible for the vertical transport of dissolved CO2 in hydroelectric reservoirs. This combined approach of measurements and numerical modeling confirmed certain hypotheses concerning the missing source of CO2, the existence of a spring peak of CO2 emission and an intense fall peak of CO2 emission for deep reservoirs. Moreover, a relation between differences in patterns of CO2 emission and reservoir depth was highlighted. It is shown that the numerical model developed in this research can be used to develop sampling strategies based on the characteristics of temporal and spatial distributions associated with each reservoir.
Cr‐pyrope garnets in the lithospheric mantle 2. Compositional populations and their distribution in time and space
Authors: Griffin W. L. , Fisher N. I. , Friedman J. H. , O'Reilly Suzanne Y. , Ryan C. G.
Published: December 2002

Three novel statistical approaches (Cluster Analysis by Regressive Partitioning [CARP], Patient Rule Induction Method [PRIM], and ModeMap) have been used to define compositional populations within a large database (n > 13,000) of Cr‐pyrope garnets from the subcontinental lithospheric mantle (SCLM). The variables used are the major oxides and proton‐microprobe data for Zn, Ga, Sr, Y, and Zr. Because the rules defining these populations (classes) are expressed in simple compositional variables, they are easily applied to new samples and other databases. The classes defined by the three methods show strong similarities and correlations, suggesting that they are statistically meaningful. The geological significance of the classes has been tested by classifying garnets from 184 mantle‐derived peridotite xenoliths and from a smaller database (n > 5400) of garnets analyzed for >20 trace elements by laser ablation microprobe–inductively coupled plasma‐mass spectrometry (LAM–ICPMS). The relative abundances of these classes in the lithospheric mantle vary widely across different tectonic settings, and some classes are absent or very rare in either Archean or Phanerozoic SCLM. Their distribution with depth also varies widely within individual lithospheric sections and between different sections of similar tectonothermal age. These garnet classes therefore are a useful tool for mapping the geology of the SCLM. Archean SCLM sections show high degrees of depletion and varying degrees of metasomatism, and they are commonly strongly layered. Several Proterozoic SCLM sections show a concentration of more depleted material near their base, grading upward into more fertile lherzolites. The distribution of garnet classes reflecting low‐T phlogopite‐related metasomatism and high‐T melt‐related metasomatism suggests that many of these Proterozoic SCLM sections consist of strongly metasomatized Archean SCLM. The garnet‐facies SCLM beneath Phanerozoic terrains is only mildly depleted relative to Primitive Upper Mantle (PUM) compositions. These data emphasize the secular evolution of SCLM composition defined earlier [Griffin et al., 1998, 1999a] and suggest that at least part of this evolutionary trend reflects reworking and refertilization of SCLM formed in the Archean time.
Paleosecular variation of brunhes age lava flows from British Columbia, Canada
Authors: Mejia Victoria , Barendregt Rene W. , Opdyke Neil D.
Published: December 2002

Brunhes age lava flows have been sampled for paleosecular variation studies from several volcanic fields of southern British Columbia (Silverthrone, Garibaldi Lake, Mt. Meager, Clearwater‐Wells Gray Park and Kelowna area). A total of 52 lava flows were sampled and 7 to 10 samples were drilled at each site. Previous radiometric studies indicate that the ages of these lava flows range from 2.3 to 760 Ka. Stepwise thermal demagnetization (14 to 21 steps) was carried out for all the samples in each site and AF demagnetization was performed on one sample per site. Forty‐five sites were selected based on rigorous criteria (α95 ≤ 5°) to calculate a mean direction (D = 356.9°, I = 70.2°, α95 = 2.8°) that is statistically indistinguishable from the direction of the dipole field at the area (I = 68.3°). Virtual geomagnetic poles (VGPs) do not show the far‐sided effect and the angular standard deviation is 17.5°, a value in agreement with the paleomagnetic field dispersion for that latitude. These high quality results are expected to improve the time averaged field (TAF) and secular variation models.
Global middle Pliocene biome reconstruction: A data/model synthesis
Authors: Haywood Alan M. , Valdes Paul J. , Francis Jane E. , Sellwood Bruce W.
Published: December 2002

The middle Pliocene warm interval (ca. 3 Ma BP) has been extensively studied. However, our knowledge concerning the global distribution of middle Pliocene biomes remains far from complete. This paper presents the results from a “first attempt” at simulating the distribution of different mid‐Pliocene biomes using an advanced numerical general circulation climate model (Hadley Centre Atmospheric Model Version 3) and the BIOME 4 vegetation model. The modeling indicates that during the middle Pliocene the geographical coverage of tundra type biomes may have been significantly reduced compared with the present day in the Northern Hemisphere. High‐latitude forests expand in the place of tundra forms of vegetation. Total area covered by forest increases for the Pliocene case compared with the present day. Arid deserts become less prevalent in the Pliocene scenario and are replaced by tropical xerophytic shrublands and savanna‐type vegetation. These results compare favorably with geological data in general and with the U.S. Geological Survey's PRISM2 middle Pliocene vegetation reconstruction, although data/model inconsistencies are apparent. Although some of these inconsistencies relate to the weaknesses of the climate and biome model employed, others identify deficiencies in the extant geological data set or the interpretation of this data. This modeled biome reconstruction will serve as a useful vehicle for aiding in future comparisons between geological data on middle Pliocene biomes and model predictions.
On the evolution of coastally trapped waves generated by Hurricane Juliette along the Mexican West Coast
Authors: Zamudio Luis , Hurlburt Harley E. , Metzger E. Joseph , Smedstad Ole Martin
Published: December 2002

An operational real‐time eddy‐resolving (1/16°) global ocean nowcast/forecast system is used to study the evolution of two coastally trapped waves generated by Hurricane Juliette along the Mexican West Coast. Results indicate that the first wave was generated along mainland Mexico and it propagated poleward as a free coastally trapped wave; it also generated anticyclonic eddies near Cabo Corrientes and the María Islands. Upon entering the Gulf of California the wave weakened cyclonic eddies and after reaching the shelf break north of Guaymas, it reversed direction and propagated southward along the east coast of the Baja California Peninsula (BCP). Next, the wave generated an anticyclonic eddy at Cabo San Lucas. Finally, the wave weakened while exiting the gulf and propagated northward along the BCP West Coast. The second coastally trapped wave was generated by Juliette's poleward winds along the BCP West Coast, but was subsequently greatly weakened by Juliette's equatorward winds.
Source mechanism of very‐long‐period signals accompanying dome growth activity at Merapi volcano, Indonesia
Authors: Hidayat D. , Chouet B. , Voight B. , Dawson P. , Ratdomopurbo A.
Published: December 2002

Very‐long‐period (VLP) pulses with period of 6–7s, displaying similar waveforms, were identified in 1998 from broadband seismographs around the summit crater. These pulses accompanied most of multiphase (MP) earthquakes, a type of long‐period event locally defined at Merapi Volcano. Source mechanisms for several VLP pulses were examined by applying moment tensor inversion to the waveform data. Solutions were consistent with a crack striking ∼70° and dipping ∼50° SW, 100m under the active dome, suggest pressurized gas transport involving accumulation and sudden release of 10–60 m3 of gas in the crack over a 6s interval.
Mechanisms controlling the global oceanic distribution of the inert gases argon, nitrogen and neon
Authors: Hamme Roberta C. , Emerson Steven R.
Published: December 2002

Dissolved inert gas measurements in the ocean yield important information about processes that occur during water mass formation. We present argon, nitrogen, and neon data from the subtropical and subpolar North Pacific and the subtropical North Atlantic. All three gases were supersaturated at the surface. In the deep ocean, Ar and N2 were undersaturated while Ne remained supersaturated. All the data fell within the range predicted by a quasi‐steady‐state mixed‐layer model that allows only temperature change, and diffusive and bubble‐mediated gas exchange. This result suggests that these three processes are the first order controls on the global oceanic distribution of inert gas saturations.
Ocean response to meridional ekman transport in the Atlantic and implication for gravity missions
Authors: Ganachaud Alexandre , Mercier Herlé
Published: December 2002

Wind friction at the ocean surface introduces energetic variations in the net mass transport across the oceanic basins. To conserve mass, the whole water column adjusts rapidly, introducing a depth‐independent perturbation in the pressure field. This signal is analyzed in a high resolution numerical model of the Atlantic Ocean. While the pressure perturbation cannot be extracted from the energetic sea surface height signals, it represents up to 90% of the bottom pressure signal when integrated across the Atlantic Ocean in the daily and monthly frequencies. This signal will be an important part of the signal measured by the GRACE (Gravity Recovery And Climate Experiment) mission.
Differences in attenuation among the stable continental regions
Authors: Bakun W. H. , McGarr A.
Published: December 2002

There are systematic differences in the attenuation of damaging earthquake ground motions between different stable continental regions (SCRs). Seismic intensity and weak‐motion data show that the attenuation in seismic waves for eastern North America (ENA) is less than for India, Africa, Australia, and northwest Europe. If ENA ground‐motion attenuation relations are used in seismic hazard models for other SCRs, as is commonly done, then the estimated ground motions and resulting hazard may be too large. If an attenuation model that averages observations from ENA and the other SCRs is used to estimate the magnitudes of large historical earthquakes in ENA, as is the case for recent estimates of M for the 1811–1812 New Madrid, Missouri and the 1886 Charleston, South Carolina events, then the magnitude estimates for these events will be too large, as will be the resulting hazard.
Salinity and temperature structure of a freezing Arctic fjord—monitored by white whales (Delphinapterus leucas)
Authors: Lydersen Christian , Nøst Ole Anders , Lovell Phil , McConnell Bernie J. , Gammelsrød Tor , Hunter Colin , Fedak Michael A. , Kovacs Kit M.
Published: December 2002

In this study we report results from satellite‐linked conductivity‐temperature‐depth (CTD) loggers that were deployed on wild, free‐ranging white whales to study the oceanographic structure of an Arctic fjord, Storfjorden, Svalbard. The whales dove to the bottom of the fjord routinely during the study and occupied areas with up to 90% ice‐cover, where performance of conventional ship‐based CTD‐casts would have been difficult. During the initial period of freezing in the fjord, over a period of approximately 2 weeks, 540 CTD profiles were successfully transmitted. The data indicate that Storfjorden has a substantial inflow of warm North Atlantic Water; this is contrary to conventional wisdom that has suggested that it contains only cold Arctic water. This study confirms that marine‐mammal‐based CTDs have enormous potential for cost‐effective, future oceanographic studies; many different marine mammal species target oceanographic discontinuities for foraging and thus may be good ‘adaptive samplers’ that naturally seek areas of high oceanographic interest.
Sea surface state measured using GPS reflected signals
Authors: Rius Antonio , Aparicio Josep M. , Cardellach Estel , Martín‐Neira Manuel , Chapron Bertrand
Published: December 2002

We discuss an airborne experiment aimed to establish the potential of the PARIS concept (PAssive Reflectometry and Interferometry System) to retrieve small features in the sea surface topography. The date and location were chosen to coincide with a TOPEX/POSEIDON (T/P) overflight. The signals of the Global Positioning System (GPS) reflected off the sea surface are tracked and compared to the directly received ones, to compute the relative delays. The features detected in the peak tracking are likely caused by topographic and sea roughness variations. While very promising, these results open the challenge to use additional information to appropriately separate both contributions.
Continued convection and the initial recovery of Dst
Authors: O'Brien T. P. , McPherron R. L. , Liemohn M. W.
Published: December 2002

We test the hypothesis that abrupt cessation of solar wind driving results in a different recovery profile for Dst than does a slow cessation. The difference arises when abrupt cessation of convection causes a large portion of the asymmetric ring current to be trapped, whereas continued, weakened convection permits a rapid initial loss of ring current particles through the dayside magnetopause. Specifically, we compare the initial recovery of the hourly Dst index for storms with gradual versus abrupt northward turning of the interplanetary magnetic field (IMF). We consider only storms with minimum Dst between −150 nT and −300 nT. We show that storms with abrupt northward turnings show the same recovery in the first 6 hours or slightly more recovery than do the storms with gradual northward turnings. Our results contradict the hypothesis that the rate of northward turning (i.e., shutoff of convection) largely determines the initial rate of recovery in Dst.
Seismotomography of the crust in the transition zone between the southern Tyrrhenian and Sicilian tectonic domains
Authors: Neri G. , Barberi G. , Orecchio B. , Aloisi M.
Published: December 2002

A crustal tomography of seismic wave velocity was performed in the contact zone between the southern Tyrrhenian, Sicilian and Ionian tectonic units, a zone where the lithospheric structure can be expected to furnish evident signatures of dynamics related to the Tyrrhenian subduction process. A dataset of 10241 P and 5597 S readings from 932 local earthquakes recorded between 1978 and 2001 by stations operating in Sicily and Calabria was inverted by the SIMULPS12 algorithm for simultaneous computation of hypocenter parameters and Vp and Vp/Vs three dimensional distributions. The study brought significant improvement in the knowledge of the local velocity structure, furnishing new information useful to better identify the local tectonic units. The results appear to be compatible with the most recent hypotheses regarding the geodynamics of the study region.
Ancient thermal anomaly of an active fault system: Zircon fission‐track evidence from Nojima GSJ 750 m borehole samples
Authors: Murakami Masaki , Tagami Takahiro , Hasebe Noriko
Published: December 2002

To understand better heat generation and transfer along faults, fission track (FT) thermochronologic analysis was performed on zircon separates from Cretaceous granitic rocks around the Nojima fault, activated during the 1995 Kobe earthquake. Samples were collected from the Geological Survey of Japan (GSJ) 750 m borehole and nearby outcrop. Zircon FTs showed reduced mean lengths and ages for samples less than ∼10 m away from the fault at depth. This is interpreted as representing an ancient thermal anomaly by heat transfer or dispersion via fluids at the deep crustal interior because the degree of FT annealing is correlated to that of deformation/alteration of borehole rocks. From extrapolation of data in the mean FT age‐length plot as well as from model age calculation, it is suggested that last cooling took place at ∼30–40 Ma.
Inertial instability and sea spirals
Authors: Shen Colin Y. , Evans Thomas E.
Published: December 2002

The ubiquitous occurrence of submesoscale cyclonic spirals in the sea as inferred from space imagery is interpreted in terms of the inertial instability of a horizontally sheared current in the oceanic mixed layer. The instability is shown to weaken anticyclonic current shear while enhancing cyclonic shear, which, in turn, becomes unstable and creates a cyclonic vortex; concurrently, surface tracer particles concentrated along the evolving cyclonic shear are wound up into a spiral, mimicking the spiral slick patterns seen in the imagery. The entire process, investigated with a fully nonlinear nonhydrostatic 3D numerical model, is contrasted with the baroclinic frontal process considered previously. The differences point to a clear need for field observations of this significant phenomenon, which are presently almost totally lacking.
Dependence of the structure of the Northern Hemisphere annular mode on the polarity of ENSO
Authors: Quadrelli R. , Wallace J. M.
Published: December 2002

The structure of the Northern Hemisphere annular mode (NAM) is shown to be significantly different during warm and cold winters of the ENSO cycle. During warm winters the Arctic center of action of the annular mode is more prominent and extends deeper into Siberia, its related surface air temperature signal is stronger, and the compensating outer ring in the sea‐level pressure field is much broader, encompassing the entire tropics. During cold winters the NAM signature is much more pronounced over the Pacific sector: the sea‐level pressure pattern exhibits a North Pacific center of action, positively correlated with the Atlantic center, and pronounced deflections of the storm track are also evident. It is suggested that the former features are associated with the equatorward displacement of the jet stream and the storm tracks during warm winters of the ENSO cycle and the latter is related to the the more pronounced break in the subtropical jet stream over the Pacific sector during cold winters.
Sea level in the Mediterranean Sea: The contribution of temperature and salinity changes
Authors: Tsimplis Michael N. , Rixen Michel
Published: December 2002

The steric sea level variability in the Mediterranean Sea is estimated from the Medar climatology. Temperature variations cause most of the overall steric sea level change in the upper 400 m. Between 1960 and the 1990s cooling of the upper waters of the Eastern Mediterranean caused reduction in the steric heights while after 1993 warming caused sea level to rise. The steric sea level changes in the upper waters of the Adriatic and the Aegean Sea are correlated with the North Atlantic Oscillation. The comparison between the steric sea levels and coastal tide‐gauges is unsatisfactory. This discrepancy questions both the practice of estimating basin‐wide sea level changes on point measurements and the use of steric height variations as measures of sea level variability in areas less sampled than the Mediterranean. Moreover the diverse behaviour of the Eastern Mediterranean at sub‐basin scales questions the meaningfulness of climatic basin averages.
A simple coupled model of tropical Atlantic decadal climate variability
Authors: Kushnir Yochanan , Seager Richard , Miller Jennifer , Chiang John C. H.
Published: December 2002

A linear, zonally averaged model of the interaction between the tropical Atlantic (TA) atmosphere and ocean is presented. A balance between evaporation and meridional heat advection in the mixed layer determines the sea surface temperature tendency. The atmosphere is a fixed‐depth, sub‐cloud layer in which the specific humidity anomaly is determined by a steady‐state balance between evaporation, meridional advection, and a parameterized humidity exchange with the free atmosphere. When the model is integrated, forced with observed surface wind anomalies from 1965 to the present, its simulation of the observed sea surface temperature (SST) is realistic and comparable to a simulation with a full ocean GCM. A statistical representation of surface winds and their relationship to the SST gradient across the equator is used to formulate and test a coupled model of their regional variability. Forced on both sides of the equator, in the trade‐wind regions, with “white‐noise” windspeed perturbations, the SST‐wind relationship in the near‐equatorial region feeds back positively on existing SST anomalies and gives rise to decadal variability.
Solid‐body rotation in the northern hemisphere summer stratosphere
Authors: Piani C. , Norton W. A.
Published: December 2002

The summer stratospheric flow is analysed in three years of ECMWF analyses. By diagnosing the angular rotation, it is shown that the summer stratospheric flow is close to solid‐body rotation for latitudes north of 30° with the rate of rotation increasing approximately linearly with height. This flow configuration is not in the radiatively determined state. The winds in thermal wind balance with the radiatively determined temperatures are unstable to barotropic/baroclinic instability. Small amplitude waves are diagnosed in the ECMWF analyses with periods of 5–10 days. These may drive the flow away from the radiatively determined state and lock the flow in the upper stratosphere into near solid‐body rotation.
Fast flow during current sheet thinning
Authors: Nakamura R. , Baumjohann W. , Runov A. , Volwerk M. , Zhang T. L. , Klecker B. , Bogdanova Y. , Roux A. , Balogh A. , Rème H. , Sauvaud J. A. , Frey H. U.
Published: December 2002

In this paper we report Cluster observation of a fast flow event in the plasma sheet associated with a small auroral substorm intensification at 1838 UT on August 12, 2001. Cluster, located in the plasma sheet, experienced significant thinning of the current sheet associated with a high‐speed Earthward flow of 900 km/s. By using the four spacecraft magnetic field data and a Harris‐type current sheet model, it was estimated that the thickness of the current sheet changes from about 1 RE before the flow observation down to 400 km, i.e., close to the ion inertia length. In the vicinity of this thin current sheet there were also signatures of enhanced current density off the center of the neutral sheet, consistent with recent Geotail results.
Factors influencing the island‐mass effect of the Galápagos Archipelago
Authors: Palacios Daniel M.
Published: December 2002

Enhanced phytoplankton biomass in the wake of the Galápagos Islands is thought to result from an island‐mass effect (IME) fueled by upwelling of the Equatorial Undercurrent (EUC) and by natural iron enrichment from the island platform. Annual means of five variables describing the thermocline, the pycnocline, and the availability of nitrate at the surface were derived from the World Ocean Atlas 1998 (WOA98). The first principal component of these variables explained 55.8% of the variance, corroborating that the Galápagos IME is associated with features of the EUC, mainly a shallow thermocline/pycnocline and its vertical spreading in the vicinity of the Galápagos. Regression analysis of SeaWiFS‐derived chlorophyll‐a (chl) on the WOA98 variables indicated that the depth of the thermocline and nitrate availability explain 91.9% of the chl variance. A secondary IME of enhanced chl levels associated with the wind‐sheltered area north of Isabela Island was evident in the residual variability.