bluuebunny/crossref_metadata_2025 huggingface dataset:
The deep currents in the Eastern Equatorial Atlantic Ocean
Authors: Bourlès B. , Andrié C. , Gouriou Y. , Eldin G. , du Penhoat Y. , Freudenthal S. , Dewitte B. , Gallois F. , Chuchla R. , Baurand F. , Aman A. , Kouadio G.
Published: May 2003

In the Atlantic Ocean, equatorial deep jets have been observed in the central and western equatorial basin. Here, we present three meridional velocity sections carried out in boreal summer 2000 in the eastern equatorial Atlantic. At that time, the deep equatorial jets were observed to weaken or to vanish in the Gulf of Guinea toward the African coast. At 10°W, the comparison with currents measured one year before, in boreal summer 1999, along with tracer distributions confirm the existence of an eastward route along the equator of part of the North Atlantic Deep Water.
A three‐dimensional study of a crustal low velocity region beneath the 9°03′N overlapping spreading center
Authors: Bazin S. , Harding A. J. , Kent G. M. , Orcutt J. A. , Singh S. C. , Tong C. H. , Pye J. W. , Barton P. J. , Sinha M. C. , White R. S. , Hobbs R. W. , Van Avendonk H. J. A.
Published: May 2003

Overlapping spreading centers (OSCs) play a key role in models of magma distribution at fast spreading ridges. To investigate the relationship between ridge‐axis discontinuities and magma supply, we conducted a three‐dimensional seismic reflection and tomography experiment at the 9°03′N OSC along the East Pacific Rise. Tomographic analysis imaged a broad mid‐crustal low velocity zone (LVZ) beneath parts of the overlapper and the associated overlap basin, demonstrating that it is magmatically robust. The complementary datasets reveal a complex storage and tapping of melt: the LVZ and melt sill at either end of the overlap basin are not simply centered beneath the rise crest but are skewed inwards. The subsequent focussing of the LVZ and sill beneath the axis of the eastern limb appears to be due to melt migration toward the tip. The OSC western limb is less magmatically robust and may be in the process of dying.
Time scales of upper ocean temperature variability inferred from the PIRATA data (1997–2000)
Authors: Wainer Ilana , Clauzet Gabriel , Servain Jacques , Soares Jacyra
Published: May 2003

Time series from the PIRATA 10‐minute measurements are investigated in order to study the upper‐ocean thermal field time‐scales of variability using the serial covariance power spectra method and wavelet analysis. This is one of the few studies that analyze in time and space the PIRATA buoy data in the region. Analysis of the depth of the 20°C isotherm show distinct patterns for the northwestern Atlantic at 8N–38W and the southeastern Atlantic, at 10S–10W. In the west, warm surface waters are accompanied by a shallower thermocline while in the east warm surface waters are associated with its deepening, consistent with Houghton [1991]. At higher frequencies the dominant signals in sea surface temperature are the diurnal and semi‐diurnal cycles. Spectral analysis of the depth of the 20°C isotherm show a predominance of the semi‐diurnal period. In the eastern Atlantic there are two additional dominant bands in the spectra: 10–14 days, 25–27 days and for the depth of the 20°C isotherm there is also a lower frequency band at 20–40 days associated with tropical instability waves at the equator. The first band can be associated with atmospherically forced motions and the lower frequency band with barotropic instability waves.
Ground rotational motions of the 1999 Chi‐Chi, Taiwan earthquake as inferred from dense array observations
Authors: Huang Bor‐Shouh
Published: May 2003

Large rotational motions excited by the 1999 Chi‐Chi, Taiwan earthquake are inferred from a dense acceleration array near the northern end of the rupture fault where large surface slips along the fault are observed. The estimated major frequency content is from 0.1 to 1.0 Hz with a peak near 0.2 Hz. It is found that in the footwall region the observed strong rotational ground motions were most probably excited by the slip of the northern rupture ending segment of the Chi‐Chi earthquake fault and that its thrust slips induced a major rock motion in the radial component. The analysis here indicates that during the Chi‐Chi earthquake significant rotation seismic energy was radiated from the bent northern end of the earthquake fault. Further analysis of rotational ground motions may provide useful constraints for its rupture mechanisms.
Operational impacts of space weather
Authors: Lambour R. L. , Coster A. J. , Clouser R. , Thornton L. E. , Sharma J. , Cott T. A.
Published: May 2003

Space weather events on the Sun, such as coronal mass ejections and solar flares, can lead to a worldwide disturbance of the geomagnetic field and associated ionospheric and thermospheric disturbances. These events can, and do, impact the performance and reliability of space‐based and ground‐based operational systems. This paper presents specific examples of the operational impact of space weather events on space surveillance systems. The paper concentrates on the 14 July 2000 event during which the solar‐terrestrial environment experienced its largest disturbance in the past 11 years. We report on effects that were detected during the July storm with the Space‐Based Visible (SBV) sensor, a visible‐band electro‐optical system that operates as a contributing sensor for the U. S. Space Surveillance Network. We also discuss the impact of this space weather event on the Global Positioning System (GPS) and on satellite tracking observations by ground‐based radars.
Chemical characteristics of groundwater around the Mozumi‐Sukenobu fault and the implication for fault activity
Authors: Satake Hiroshi , Murata Masanobu , Hayashi Haruna
Published: May 2003

A change in the chemical composition of the groundwater from Ca‐HCO3 type to Na‐HCO3 type with decreasing distance from a fault zone is observed along an active fault survey tunnel in central Japan. The sodium/calcium ratio in the groundwater is maximum (ca. 10–25) in and adjacent to the area of the significantly fractured fault zone. The ratio decreases with increasing distance from the fault zone. This may result from Na release from plagioclase into the groundwater due to the intense chemical weathering in the fault zone. Thus, the Na/Ca ratio in the groundwater around the fault has the potential to be a good indicator of fault activity. Based on the oxygen isotope ratio and tritium content in groundwater, one fault is inferred to be fairly permeable and the other impermeable. This implies that the former is active and the latter inactive.
Effects of inelasticity on the apparent depth and detectability of seismic discontinuities in the mantle
Authors: Liu Kelly H.
Published: May 2003

Accurate determination of parameters about seismic discontinuities in the earth, such as their depth, existence, and strength, provides critical information about the physical and chemical states and dynamics of the earth's interior. Unfortunately, those parameters can be strongly affected by factors that are not related to the discontinuities. We use synthetic seismograms to estimate the influence of one of those factors, inelasticity, on the apparent depth and detectability of the 410‐ and 660‐ kilometer discontinuities obtained from stacking P‐to‐S converted phases (PdS). Our results show that when PdS travels through a zone with lower‐than‐normal Q values, the observed depth of discontinuities could be tens of kilometers deeper than the real value, and the stacking amplitudes and consequently the detectability and apparent strength are greatly reduced. This study demonstrates the importance of taking Q structure into account when seismologically detected discontinuity parameters are interpreted.
Along or across front survey strategy? An operational example at an unstable front
Authors: Rixen M. , Allen J. T. , Alderson S. , Cornell V. , Crisp N. , Fielding S. , Mustard A. T. , Pollard R. T. , Popova E. E. , Smeed D. A. , Srokosz M. A. , Barth A. , Beckers J.‐M.
Published: May 2003

We present results of the optimization of near‐real time on‐board sampling strategy in the Iceland‐Faroes oceanic frontal area, based on the outputs of a mesoscale 3D operational data assimilation forecasting experiment. By minimizing a root mean square error cost function, we show that in this example an along‐front sampling strategy, i.e. with transects parallel to the front, produces smaller errors in temperature, salinity, nitrate, phytoplankton, and zooplankton fields, as a result of a combination of the direction of the sampling of the front and errors associated with the asynopticy of observations (Doppler effect). This is contrary to the classic across‐front sampling strategies that are used in most field experiments reported in the literature, i.e. where transects are perpendicular to the front. A control model shows that at these spatio‐temporal scales, the along front sampling strategy is optimal when the frontal instability has sufficiently developed.
Seismic observation of narrow plumes in the oceanic upper mantle
Authors: Li X. , Kind R. , Yuan X. , Sobolev S. V. , Hanka W. , Ramesh D. S. , Gu Y. , Dziewonski A. M.
Published: May 2003

We have found seismic evidence for the existence of narrow (about 200 km diameter) and hot plumes in the upper mantle above the 410 km discontinuity. They are located mainly under ocean islands, not however, under the central parts of major continents. These results are obtained from comparing globally the observed travel time differences between Ps conversions and SS precursors from the discontinuity at 410 km depth, using published data and new observations from ocean island stations. Comparison of SS precursors and Ps conversions, however, leads also to indications of significantly fewer narrow plumes in the upper mantle transition zone between 410 and 660 km depth, than in the upper mantle above 410 km depth.
Embedding a SST anomaly model in to a z‐coordinate oceanic GCM for producing El Niño oscillation in the tropical Pacific climate system
Authors: Zhang Rong‐Hua , Zebiak Stephen E.
Published: May 2003

The sensitivity of simulated interannual variability to thermocline impacts on sea surface temperature (SST) is examined in a hybrid coupled model (HCM) of the tropical Pacific climate system, consisting of the latest version of the GFDL/NOAA Modular Ocean Model (MOM 3) and the atmospheric component of the Cane‐Zebiak (CZ) coupled model. Standard coupling of the two components has difficulty producing El Niño‐like oscillations, apparently due in part to the ocean general circulation model's (OGCM) problems in the far eastern equatorial Pacific, where the modeled subsurface influence on the SST is very weak. Analogous to the CZ model, a separate diagnostic SST anomaly model is explicitly embedded into the z‐coordinate OGCM, serving as an interface between the ocean and atmosphere in the HCM. The three components exchange anomaly information only. This embedding strategy has a significant effect on the coupled variability in the model system. Incorporating the embedded SST anomaly equation, in which the thermocline effect on SST is enhanced in the eastern equatorial Pacific, the HCM simulations exhibit oscillations on interannual time scales for a range of parameters. It is shown that the most realistic coupled behavior (e.g., 3–4 year oscillation) results from the appropriate depiction of entrainment temperature (Te) in association with the thermocline depth anomalies. The results support the hypothesis that current mixing parameterization in the OGCM is problematic in depicting vertical turbulent processes.
Incoherent scatter radar plasma density measurements at Jicamarca using a transverse‐mode differential‐phase method
Authors: Kudeki Erhan , Woodman Ronald F. , Feng Zhaomei
Published: May 2003

The 50 MHz Jicamarca incoherent scatter radar can be used to make very high precision F‐region plasma drift measurements with less than a m/s uncertainty and 5 min/15 km time/height resolutions. In such measurements the transmitting antenna beam is pointed perpendicular to the geomagnetic field [e.g., Kudeki et al., 1999] and backscattered fields consist of magneto‐ionic O‐ and X‐components with unequal phase retardations. Detecting the fields with an orthogonal pair of linear‐polarized antennas and fitting the average power and differential‐phase of the antenna outputs to an appropriate data model we have succeeded in making F‐region electron density measurements with data collected during Jicamarca drifts experiments. This procedure provides Jicamarca with a new capability for simultaneous drifts and density measurements at F‐region heights.
Evidence for both crustal and mantle earthquakes in the subducting Juan de Fuca plate
Authors: Cassidy John F. , Waldhauser Felix
Published: May 2003

We investigate the relationship between high‐precision hypocentres in the subducting Juan de Fuca plate beneath southwest British Columbia, and the velocity structure from receiver function analysis and reflection seismic data. 108 earthquakes at depths of 40 to 65 km were relocated using a double‐difference algorithm to obtain precise earthquake locations. Correlation of the relocated seismicity with structural information shows a concentration of earthquakes near the top of the subducting oceanic crust, and a deeper layer of seismicity in the uppermost mantle of the subducting Juan de Fuca plate. The strong correlation of the seismicity with the structure of the subducting plate suggests that seismic failure is caused by changes in mechanical strength within the plate, supporting the hypotheses that phase transformations and thermal‐petrological conditions play an important role in the seismogenesis of double‐seismic zones.
Southern Ocean sea‐ice control of the glacial North Atlantic thermohaline circulation
Authors: Shin Sang‐Ik , Liu Zhengyu , Otto‐Bliesner Bette L. , Kutzbach John E. , Vavrus Stephen J.
Published: May 2003

A coupled model simulates a shallower and weaker North Atlantic Deep Water circulation at the Last Glacial Maximum, compared to the modern, with an enhanced intrusion of Antarctic Bottom Water into the North Atlantic. These circulation changes are caused by the enhanced Antarctic Bottom Water formation, which is triggered by the enhanced equatorward sea‐ice transport, ultimately by increased westerlies, in the Southern Ocean at the Last Glacial Maximum.
Multiresolution spatial characterization of land degradation phenomena in southern Italy from 1985 to 1999 using NOAA‐AVHRR NDVI data
Authors: Lanfredi M. , Lasaponara R. , Simoniello T. , Cuomo V. , Macchiato M.
Published: May 2003

NOAA‐AVHRR images (1985–1999) at full spatial resolution (1.1 km2) were exploited for studying land degradation phenomena in Southern Italy. We analyzed the spatial map of the correlation coefficient between NDVI and time by using wavelet transform. Multiscale aggregations of negative trends were searched for detecting spatially diffused phenomena of decrease in vegetation activity. The analysis mainly selects an extended area in a region considered vulnerable to desertification. Our results indicate that multiresolution AVHRR/NDVI analysis can be very useful for monitoring the complex spatio‐temporal dynamics of vegetation activity in landscapes characterized by heterogeneity scales similar to those of Southern Italy.
Systematic error aspects of gauge‐measured solid precipitation in the Arctic, Barrow, Alaska
Authors: Sugiura Konosuke , Yang Daqing , Ohata Tetsuo
Published: May 2003

This report provides insight into systematic errors of gauge‐measured precipitation in the Arctic by the precipitation gauge intercomparison experiment at Barrow, Alaska. Reference gauges and various national standard gauges used in the Arctic regions were installed. The bias of trace precipitation was recorded with high frequency and varied widely from 6 to 130% increase of the gauge‐measured amounts due to a variety of gauge types. The blowing snow experiment showed that the number flux of aeolian snow particles at a gauge orifice height verily increased with the occurrence of blowing snow, and it seems reasonable to suppose that blowing snow particles are an overestimation bias of gauge‐measured precipitation. These suggest that the systematic errors of gauge‐measured precipitation for Arctic conditions must mainly take into consideration of not only wind‐induced undercatch, wetting and evaporation losses, but also the influence of blowing snow and trace precipitation loss.
Observation of tetravalent cerium in zircon and its reduction by radiation effect
Authors: Takahashi Y. , Sakashima T. , Shimizu H.
Published: May 2003

The oxidation state of Ce in zircons of the Cretaceous Habu and Yamanaka granodiorite from Southwest Japan was measured by Ce LIII‐edge X‐ray absorption near‐edge structure (XANES). The results confirmed that tetravalent Ce is incorporated in zircon, as estimated from the positive Ce anomaly in the REE pattern of zircons. However, the CeIV percentage in Yamanaka zircon is much smaller than expected from the degree of its Ce anomaly. The γ‐irradiation experiments suggest that the decrease of CeIV can be well explained by the reductive reaction of CeIV to CeIII by the radiation effect due to U and Th in the zircon. This suggests that it is possible to date zircon by the amount of Ce reduced after sample formation. As shown in this, it is possible to deduce geochemical information by comparing the CeIV percentage at present given by XANES and the initial CeIV percentage estimated from Ce anomaly.
The impact of sea surface temperature on the North American monsoon: A GCM study
Authors: Yang Zong‐Liang , Gochis Dave , Shuttleworth William James , Niu Guo‐Yue
Published: May 2003

The NCAR CCM3 was used to simulate the circulation and rainfall patterns of the North American monsoon system (NAMS). When forced with repeated annual cycles of climatological average sea surface temperatures (SSTs), the CCM3 significantly under‐represents monsoon rainfall in the southwest United States while simulating excessive precipitation in the tropical eastern Pacific Ocean and the Caribbean Sea. However, when forced with the observed monthly average SSTs from 1979 to 1997, the CCM3 produces an improved simulation of monsoon rainfall in the southwestern U.S., as well as in the eastern tropical Pacific Ocean and the Caribbean Sea. Using the SSTs for 1983 in the Pacific and climatological SSTs elsewhere, the modeled circulation and rainfall distribution resembles that given with observed monthly average SSTs. The simulations are sensitive to the size of the domains over which the Pacific SST anomalies are imposed. Overall, these results suggest that the magnitude and size of winter‐ and springtime Pacific SST anomalies have a significant influence on summertime rainfall in the southwest U.S., and that these SSTs contribute to the NAMS precipitation climatology in extreme years more than in less extreme years.
Climate and interannual variability of the atmosphere‐biosphere 13CO2 flux
Authors: Scholze M. , Kaplan J. O. , Knorr W. , Heimann M.
Published: May 2003

We present a bottom‐up approach to simulate the terrestrial isotopic carbon variations using the Lund‐Potsdam‐Jena dynamic global vegetation model (LPJ‐DGVM). LPJ is extended to include isotopic fractionation of 13C at the leaf level during assimilation and includes a full isotopic terrestrial carbon cycle. The model thus allows a quantitative analysis of the net biosphere exchange of CO2 and 13CO2 with the atmosphere as a function of changes in climate, atmospheric CO2, and the isotope ratio of CO2. LPJ simulates a global mean isotopic fractionation of 17.7‰ at the leaf level with interannual variations of ca. 0.3‰. Interannual variability in the net 13CO2 flux between atmosphere and terrestrial biosphere is of the order of 15 PgC‰ yr−1. It is reduced to 4 PgC‰ yr−1 if the leaf‐level fractionation factor is held constant at the long term mean. Taking climate driven variable fractionation effects into account in double deconvolution studies we estimate that this could imply shifts of up to 0.8 PgC yr−1 in the inferred partitioning between terrestrial and oceanic carbon sinks.
Modulation of Sri Lankan Maha rainfall by the Indian Ocean Dipole
Authors: Zubair Lareef , Rao Suryachandra A. , Yamagata Toshio
Published: May 2003

Investigating the September to December rainy season in Sri Lanka associated with the Maha rice growing season provides insights into the Asian monsoon during the boreal fall. Here, the modulation of the Maha rainfall by the tropical air_sea coupled phenomenon referred to as the Indian Ocean Dipole (IOD) is documented. The Maha rainfall has a strong and robust association with the IOD from 1869 to 2000. The anomalously warm sea surface in the western Indian Ocean associated with the positive IOD phase induces large scale convergence in the lower troposphere extending to Sri Lanka leading to the preponderant enhancement of Maha rainfall.
The role of snow cover fluctuations in multiannual NAO persistence
Authors: Bojariu Roxana , Gimeno Luis
Published: May 2003

In this article authors explore the relation in the observed data between the Eurasian snow cover anomalies and the NAO variability on interannual to decadal time scales. Results reached in this study suggest that in winter and early spring, NAO type atmospheric circulation influences the extent of snow cover and the snow cover affects the atmosphere in the late spring, summer and early autumn leading to a mechanism that seems to be responsible for the multiannual NAO persistence in the last half century.
Satellite observations of modulation of surface winds by typhoon‐induced upper ocean cooling
Authors: Lin I.‐I. , Liu W. Timothy , Wu Chun‐Chieh , Chiang J. C. H. , Sui Chung‐Hsiung
Published: May 2003

Two remote sensing data sets, the Tropical Rainfall Measurement Mission Sea Surface Temperature (SST) and the NASA QuikSCAT ocean surface wind vectors, are analysed to study ocean‐atmosphere interactions in cold SST regions formed in the trail of two typhoon events. Anomalously cold SST patches up to 6°C below the surrounding warm tropical ocean SST are found along the trail of typhoon tracks as cold, deep waters are entrained up to the mixed layer due to typhoon forcing. In both typhoon events, significant and systematic weakening of surface wind speed is found over cold SST patches relative to surface wind speed in surrounding regions. The wind speed anomalies disappear as the patches recover to the level of the surrounding SST. The results are consistent with the mechanism proposed by Wallace et al. that surface winds are modulated by SST via stability. As wind within the well‐mixed boundary layer moves over the cold patch, boundary layer stability increases, vertical mixing is suppressed, and the vertical wind shear increases; reduction in surface wind speed is caused. In particular, our result shows that this mechanism can act on relatively small spatial (≈100 km) and short (≈1 day) time scales.
TOMEX: A comparison of lidar and sounding rocket chemical tracer wind measurements
Authors: Larsen M. F. , Liu A. Z. , Bishop R. L. , Hecht J. H.
Published: May 2003

On October 26, 2000, a Black Brant V sounding rocket carrying a chemical tracer release was launched from the rocket range at White Sands, New Mexico, as part of the Turbulent Oxygen Mixing Experiment (TOMEX). The releases occurred approximately 150 km from the location of the Starfire Optical Range where the University of Illinois sodium lidar was operated to measure winds and temperatures in the mesosphere and lower thermosphere. The geometry for the experiment was such that the lidar beam was able to intersect the release point for the chemical tracer trail on the upleg part of the flight near an altitude of 95 km. In all, a total of five lidar beam directions were used to sample the region from approximately 85 to 105‐km altitude in the vicinity of the releases. Combining the lidar Doppler velocity data from the various beam directions made it possible to produce profiles of vector horizontal winds that could be compared directly with the winds obtained from the triangulation of the chemical tracer trails.
Magnetic field draping enhancement at the Martian magnetic pileup boundary from Mars global surveyor observations
Authors: Bertucci C. , Mazelle C. , Crider D. H. , Vignes D. , Acuña M. H. , Mitchell D. L. , Lin R. P. , Connerney J. E. P. , Rème H. , Cloutier P. A. , Ness N. F. , Winterhalter D.
Published: May 2003

The Magnetic Pileup Boundary (MPB) is a sharp and permanent plasma boundary located between the bow shock and the ionospheric boundary, reported so far at Mars and comets. We use Mars Global Surveyor Magnetometer data to do a quantitative analysis of the magnetic field geometry in the surroundings of the Martian MPB. As a result, we report for the first time a dramatic enhancement of the magnetic field draping at this boundary. This new feature, already reported at comets, is independent of the presence of the crustal magnetic sources. Comparisons with similar results across the Martian and cometary magnetotails reveal that the MPB and the magnetotail boundary are connected. Moreover, the study of this feature can help understand the physics of the Venusian magnetic barrier.
Modified cloud flag for SeaWiFS data over turbid water regions
Authors: Okada Yasuhiko , Mukai Sonoyo , Sano Itaru
Published: May 2003

The cloud flag algorithm, which uses the data of near infrared wavelengths, sometimes flags the turbid water region as clouds. A classification method of the cloud‐free pixels over the turbid waters from the cloud‐flagged data is proposed. SeaWiFS data around the western coast of India and other turbid water regions (La Plata River, East China Sea) are examined for our proposed algorithm.
Analogue modeling of tension fracture pattern in relation to mid‐ocean ridge propagation
Authors: Tentler Tatiana
Published: May 2003

The propagation of mid‐ocean ridges is examined by means of centrifuge models using non‐linear materials as analogues of lithospheric rocks. Fractures in the upper brittle layer propagate laterally and link together in different coalescence patterns. The geometries of the cracks developed in the initial stage of extension control their subsequent growth and coalescence.
Net accumulation of the Greenland ice sheet: High resolution modeling of climate changes
Authors: Kiilsholm Sissi , Christensen Jens Hesselbjerg , Dethloff Klaus , Rinke Annette
Published: May 2003

High‐resolution (50 km) climate change simulations for an area covering the entire Arctic have been conducted with the regional climate model (RCM) HIRHAM. The experiments were forced at the lateral boundary by large‐scale atmospheric conditions from transient climate change scenario simulations performed with the Max Planck Institute for Meteorology coupled ocean atmosphere general circulation model (OAGCM) ECHAM4/OPYC3 with a resolution of ∼300 km. The emission scenarios used were the IPCC SRES [Nakicenovic, 2000] marker scenarios A2 and B2. Three 30‐year time slice experiments were conducted with HIRHAM for periods representing present‐day (1961–1990) and the future (2071–2100) in the two scenarios. We find that due to a much better representation of the surface topography in the RCM, the geographical distribution of present‐day accumulation rates simulated by the RCM represents a substantial improvement compared to the driving OAGCM. Estimates of the regional net balance are also better represented by the RCM. In the future climate the net balance for the Greenland Ice Sheet is reduced in all the simulation, but discrepancies between the amounts when based on ECHAM4/OPYC3 and HIRHAM are found. In both scenarios, the estimated melt rates are larger in HIRHAM than in the driving model.
Mantle and crustal structure in Phoebe Regio and Devana Chasma, Venus
Authors: Kiefer Walter S. , Peterson Kelly
Published: May 2003

We use gravity and topography data to study crust and mantle structure in Phoebe Regio and Devana Chasma on Venus. We find that Phoebe is a region of thickened crust and hotter than normal mantle. These results are inconsistent with a cold, downwelling model and may support a mantle plume origin for Phoebe. However, the pattern of thermal anomalies is unusual, with temperature maxima on the periphery of the highland rather than in its center. This may reflect development of thermal boundary layer instabilities as the plume head interacts with the lithosphere. The hot mantle anomaly beneath Devana Chasma is discontinuous near latitude 10 North, coinciding with a 600 km offset in the rift zone trend. Devana should be regarded as two separate rifts, one propagating south from Beta Regio and the other propagating north from Phoebe Regio. Our results support the view that Venus remains a geologically active world.
Variability of AABW properties in the equatorial channel at 35°W
Authors: Andrié C. , Gouriou Y. , Bourlès B. , Ternon J.‐F. , Braga E. S. , Morin P. , Oudot C.
Published: May 2003

Hydrological data and tracer (silicate, oxygen and CFCs) analyses have been performed in order to describe the time and space variability of the characteristics and transport of the Antarctic Bottom Water (AABW) entering the equatorial channel at 35°W. The 35°W sections were sampled in the tropical Atlantic during several cruises from 1993 to 1999 as part of the international WOCE and CLIVAR efforts. Data for the 1990s reveal a slight warming trend superimposed on significant variability due to the seasonal changes of AABW transports. Data from previous cruises made in the 1970s and 1980s complete the time‐series and show that, over the last three decades, the maximal AABW input occurred in the early 1990s.
Conductive heat flow variations from bottom‐simulating reflectors on the Hikurangi margin, New Zealand
Authors: Henrys Stuart A. , Ellis Susan , Uruski Christopher
Published: May 2003

Bottom simulating reflectors (BSRs) represent the base of a gas hydrate zone underlain by widespread free gas. The extent of BSRs (>40,000 km2) has been mapped on the continental slope of the Hikurangi margin using industry and research seismic data. A conductive model was used to calculate heat flow from the depth of the BSR to the surface. A regional trend is observed, in which heat flow, uncorrected for sedimentation effects, decreases from an average of ∼50 mW m−2 at the toe of the accretionary prism to ∼35 mW m−2 at a distance 100 km landward from the deformation front. This trend reflects the processes of thickening accretionary wedge sediments and subduction of the Pacific plate and is in general agreement with heat flow values obtained using bottom‐hole temperature data. Local variations of heat flow were also observed, notably low and high values over the crest and flanks of anticlines. Numerical modeling indicates that much of this heat flow variation is due to a combination of variable seabed bathymetry and sedimentation effects. The dynamic effects of thrust faulting are found to be small and fluid flow along near‐surface faults is not predicted to contribute significantly to the observed heat flow anomalies along the modeled section.
Convergent flow observed in a laboratory‐scale unsaturated fracture system1
Authors: LaViolette Randall A. , Glass R. J. , Wood Thomas R. , McJunkin Timothy R. , Noah K. S. , Podgorney Robert K. , Starr Robert C. , Stoner Daphne L.
Published: May 2003

An experiment was designed to observe water flow in a simple analogue fractured rock network. The fracture network was modeled by the gaps between an array of limestone blocks, whose permutations generated different realizations of the network. Three out of five of these realizations displayed flow convergence, in contrast to that predicted by porous continuum models. Such convergence occurs because fracture intersections act as capillary barriers that integrate or focus flow within the network.
Improved normal mode constraints on lower mantle vp from generalized spectral fitting
Authors: Resovsky Joseph S. , Pestana Rita
Published: May 2003

In order to improve constraints on deep mantle vp, we use generalized spectral fitting (GSF) and data from 12 recent large earthquakes to measure normal mode structure coefficients for a set of 7 vp sensitive multiplets (7S6, 5S7, 5S8, 6S9, 6S10, 5S11, 5S12). This set includes three different classes of strong sensitivity to vp heterogeneity as a function of frequency. We have significantly improved resolution of this part of the spectrum because the use of GSF allows us to provide the first measurements of 6S9 and 5S11, which are strongly coupled to multiplets of the 7S overtone branch, while the use of an expanded data set permits refined measurements of the other multiplets. Our results are consistent with prior measurements, but reveal an inconsistency between the data and model predictions that previously had not been apparent. Recent mantle models that fit most long‐wavelength data overestimate the amplitude of degree 2 splitting coefficients for multiplets with two different types of sensitivity to vp heterogeneity. This observation implies that the strong degree 2 component of existing models of the correlation and scaling of δ ln vs and δ ln vp will need to be adjusted significantly in much of the mantle.
Along or across front ocean survey strategy? The estimation of quasi‐geostrophic vertical velocities and temperature fluxes
Authors: Rixen M. , Allen J. T. , Pollard R. T. , Beckers J.‐M.
Published: May 2003

In a companion paper we have shown that at the mesoscale, the unusual across front sampling strategy (AL) is more accurate than the usual across front sampling strategy (AC) on hydrographic and bio‐chemical properties when the front is sufficiently developed. The cruise design based on the optimal reconstruction of the density fields does however not imply that derived variables like quasi‐geostrophic (QG) vertical velocities and temperature fluxes also exhibit minimal associated errors. Here we present results of optimized sampling strategies for diagnostic QG vertical velocities (wQG) and temperature fluxes (θQG) derived from the omega equation. Results are illustrated in the same framework, for the Iceland‐Faroes oceanic frontal area and for a control model and reveal that at these spatio‐temporal scales, the unusual AL may also provide better estimations of vertical velocities and temperature fluxes compared to the classic AC, especially when the front is sufficiently developed.
ENSO related variability in the Southern Hemisphere, 1948–2000
Authors: Ribera Pedro , Mann Michael E.
Published: May 2003

The spatiotemporal evolution of Southern Hemisphere climate variability is diagnosed based on the use of the NCEP reanalysis (1948–2000) dataset. Using the MTM‐SVD analysis method, significant narrowband variability is isolated from the multi‐variate dataset. It is found that the ENSO signal exhibits statistically significant behavior at quasiquadrennial (3–6 yr) timescales for the full time‐period. A significant quasibiennial (2–3 yr) timescales emerges only for the latter half of period. Analyses of the spatial evolution of the two reconstructed signals shed additional light on linkages between low and high‐latitude Southern Hemisphere climate anomalies.
Along‐strike variations of crustal reflectivity related to the Andean subduction process
Authors: Yoon M. , Buske S. , Lüth S. , Schulze A. , Shapiro S. A. , Stiller M. , Wigger P.
Published: May 2003

This paper presents the results of Kirchhoff prestack depth migration applied to two onshore deep seismic reflection data sets (ANCORP'96 and PRECORP'95). The prestack depth migration method was implemented in 3D (ANCORP) and in 2D (PRECORP), respectively, from topography. Selective stacking of the migrated depth slices yielded a 3D depth volume (ANCORP) and a 2D depth section (PRECORP), respectively. An additional “offline stacking” provided a final 370 km long 2D depth section (ANCORP). In this paper a 180 km long depth section will be presented. At the beginning of the ANCORP section a double reflection zone is observed, which is associated with the upper and lower boundary of the oceanic crust. Except for some areas a nearly complete image of the Nazca reflector at depths between 60–90 km has been obtained. Moreover, one Bright Spot in each section has been detected: the Quebrada Blanca Bright Spot (QBBS, ANCORP) and the Calama Bright Spot (CBS, PRECORP). The reprocessing yielded two new aspects regarding these structures: Besides the west dip of the QBBS, which was already known from standard poststack processing results, a 3D analysis of the ANCORP data set shows an additional north‐dipping trend of the QBBS. Furthermore, the CBS is discovered for the first time.
Annual SST cycle in the Eastern Mediterranean, Red Sea and Gulf of Elat
Authors: Berman Tal , Paldor Nathan , Brenner Steve
Published: May 2003

The summer‐to‐winter SST difference in the Eastern Mediterranean, Red Sea and Gulf of Elat, vary from 6°C in the Red Sea and Gulf of Elat to 12°C in the Eastern Mediterranean. This dramatic difference occurs despite the similar monthly mean values of heat flux components that prevail in these seas. We show that direct mixing by the wind stress, fresh water influx or upwelling cannot account for this difference. Instead, we demonstrate the crucial role of the deep‐water temperature in determining the amplitude of the annual SST changes via its effect on the temperature gradient above the base of the permanent thermocline. Since the deep water in the Eastern Mediterranean is formed in the Aegean or Adriatic seas and not in situ, it is much colder than in the Red Sea and the Gulf of Elat. This low temperature of the deep water causes the observed, large, SST annual signal.
Equatorial forcing of interannual Rossby waves in the eastern South Pacific
Authors: Vega Andres , du‐Penhoat Yves , Dewitte Boris , Pizarro Oscar
Published: May 2003

Long baroclinic Rossby waves generated along the western coasts of continents play an important role in transferring coastal perturbations westwards into the ocean's interior. To investigate interannual Rossby waves in the eastern South Pacific (10°S to 40°S), combined TOPEX/POSEIDON and ERS‐1/2 satellite altimeter data were compared with model simulations of Rossby waves for the 1992–2000 period. The multimode linear model includes dissipation and was forced by observed wind stress curl from ERS‐1/2 and coastal pycnocline‐depth anomalies. The latter were determined by a high‐resolution eastern boundary linear model initialized by observed sea level at the equator. Strong westward propagation of pycnocline anomalies originating at the coast can be observed at least as far south as 40°S. The results suggest that an important part of the interannual mid‐latitude, free baroclinic Rossby waves originated at the coast were forced by pycnocline fluctuations originating from the equator in 1992–2000, a period which was dominated by the 1997–98 El Niño event.
Cloudiness over the contiguous United States: Contemporary changes observed using ground‐based and ISCCP D2 data
Authors: Sun Bomin
Published: May 2003

Comparisons of monthly daytime cloudiness time series of total cloud cover (TCL) and cloud types' occurrences between the ground‐based and International Satellite Cloud Climatology Project (ISCCP) D2 datasets were conducted over the contiguous United States. Despite its large bias (+6.7% to +20.8%), TCL in ISCCP D2 is highly correlated with the surface observations in all seasons. Close correspondence of seasonal and interannual variability between these two datasets is also seen in low stratiform and cirrus clouds. Reconstruction of these cloud characteristics using ISCCP data was performed for the 1990s when the Automated Surface Observation System (ASOS) implementation irreversibly broke the homogeneity of ground‐based cloudiness time series over the United States. Verification of reconstructed cloudiness characteristics was conducted using the independent in‐situ climatic variables such as diurnal temperature range and precipitation.
The salinity normalization of marine inorganic carbon chemistry data
Authors: Friis K. , Körtzinger A. , Wallace D. W. R.
Published: May 2003

Normalization to a constant salinity (S) is widely used for the adjustment of marine inorganic carbon chemistry data such as total alkalinity (AT) and total dissolved inorganic carbon (CT). This procedure traces back to the earliest studies in marine chemistry, but ignores the influence of riverine input of alkalinity and of dissolution of biogenic carbonates in the ocean. We tested different adjustment possibilities for AT and conclude that in most parts of the surface ocean the normalization concept does not reflect relationships which represent reality. In this paper, we propose a salinity adjustment based on a constant and region‐specific term for S = 0, which expresses river run off, upwelling from below the lysocline, calcification, and lateral sea surface water exchange. One application of the normalization concept is its extension to AT and also CT predictions and implementation in models. We give a brief discussion on the usage of such extensions.
Simulation of energetic particle injections associated with a substorm on August 27, 2001
Authors: Li Xinlin , Sarris T. E. , Baker D. N. , Peterson W. K. , Singer H. J.
Published: May 2003

Discrete injections of energetic electrons and ions and their subsequent drift echoes were observed shortly after 0410 UT on August 27, 2001 by three geosynchronous satellites which were arrayed on the dayside. The GOES‐8 spacecraft at geosynchronous orbit near local midnight, the four‐satellite CLUSTER constellation also near local midnight. Concurrent and POLAR was at two hours after midnight. The observations from this suite of satellites provide the basis of information and constraints for us to model the particle injections. The simulations with test‐particle simulations, reproduce both the observed electron and ion injections and subsequent drift echoes. Our simulation results support the idea that the energetic particle injections into the inner magnetosphere are a consequence of near‐Earth magnetic reconnection.
The impact of road traffic on global tropospheric ozone
Authors: Granier Claire , Brasseur Guy P.
Published: May 2003

Model calculations suggest that the emissions by road traffic (passenger vehicles and trucks) of ozone precursors (NOx, CO, hydrocarbons) have a substantial impact on the concentration of tropospheric ozone at the regional scale in the boundary layer and at the hemispheric scale in the free troposphere. Increases in the surface ozone concentration resulting from road traffic are typically 5–15 % at mid‐latitudes in the Northern hemisphere during summer. Similar levels of ozone changes are calculated in the Southern hemisphere during austral summertime, but with perturbations less uniformly distributed than in the Northern hemisphere. Ozone changes produced in the upper troposphere as a result of road traffic are of the same magnitude (5–8% in July) as the changes generated by commercial aircraft operations. A traffic‐induced reduction of 3% is estimated for the globally and annually averaged lifetime of methane.
A near‐annual coupled ocean‐atmosphere mode in the equatorial Pacific ocean
Authors: Jin Fei‐Fei , Kug Jong‐Seong , An Soon‐Il , Kang In‐Sik
Published: May 2003

A near‐annual coupled ocean‐atmosphere mode in the equatorial Pacific is studied using the NCEP ocean assimilation data set. This fast mode of tropical Pacific climate variability is superimposed on the slow 3–5 year El Niño‐Southern Oscillation (ENSO) phenomenon. Anomalous zonal advection plays a crucial role in generating this fast mode. It is suggested that this fast mode can be understood in terms of a coupled Pacific basin mode. It is responsible for the occurrence of some minor El Niño and La Niña events and has implications for the prediction of ENSO events.
Characterizing submarine groundwater discharge: A seepage meter study in Waquoit Bay, Massachusetts
Authors: Michael Holly A. , Lubetsky Jonathan S. , Harvey Charles F.
Published: May 2003

A seepage meter study was performed in Waquoit Bay on Cape Cod, Massachusetts to characterize the amount, pattern, and origin of submarine groundwater discharge. Measurements from grids of 40 seepage meters provide a detailed representation of groundwater flux in both space and time. At the head of the bay, a distinct band of high, saline discharge was observed between 25 and 45 m from the shoreline. Slug tests indicated no pattern of permeability to explain the band of discharge, and the band was not observed offshore of an island where freshwater discharge is negligible. Experiments using clusters of seepage meters showed large variability in discharge at the meter scale and similar temporal variation throughout the domain, reflecting tidal influence primarily near shore. The small‐scale variability challenges the assumption of locally homogeneous flow used in many models, and the band of discharge contradicts predictions that total outflow is largely fresh and decreases monotonically from shore.
On the unexplained stratospheric ozone losses during cold Arctic Januaries
Authors: Rex M. , Salawitch R. J. , Santee M. L. , Waters J. W. , Hoppel K. , Bevilacqua R.
Published: May 2003

Using a combination of data from Match, POAM II, POAM III and MLS we show that the chemical loss rate of Arctic O3 during January of four cold winters (1992, 1995, 1996, and 2000) is consistently faster than can be accounted for by assuming complete activation of reactive chlorine and standard reaction kinetics. However, O3 loss rates measured during late February and early March 1996 are shown to be consistent with observations of ClO. The faster than expected O3 loss rates during January are shown to occur when air parcels are illuminated at high solar zenith angles (SZAs between ∼85 and 94°), and to result in cumulative O3 loss of ∼0.5 ppmv. The cause of the rapid January O3 loss is unclear, but may be related to a photolytic process at high SZA that is poorly represented by current photochemical models.
Solar wind modulation of galactic cosmic rays
Authors: Ahluwalia H. S.
Published: May 2003

We have analyzed the annual mean hourly data for the solar wind speed (V), the interplanetary magnetic field (IMF) intensity (B), and the neutron monitor (NM) rates for 1964–1998, covering three sunspot number (SSN) cycles (20, 21, 22). The analysis brings out some of the steady state characteristics of the long‐term changes in the observed galactic cosmic ray (GCR) modulation and the ‘mini’ cycle. We find that BV time series reproduces the observed variations of a variety of phenomena, including the 11‐yr and the 27‐day GCR modulations. We reaffirm that convective removal of GCR by the solar wind accounts for a major part of the observed modulations in the inner heliosphere.
Jupiter's polar ionospheric flows: Theoretical interpretation
Authors: Cowley S. W. H. , Bunce E. J. , Stallard T. S. , Miller S.
Published: May 2003

Prompted by recent observations of ion flows from Doppler measurements of infrared auroras, we here discuss the nature of the plasma flow in Jupiter's high‐latitude ionosphere. The physical picture is based on a combination of three elements, namely an inner Hill‐type sub‐corotating region containing outward‐diffusing iogenic plasma, an outer sub‐corotating region where iogenic plasma is lost down the tail, principally in the dusk and midnight sector via the reconnection‐related Vasyliunas‐cycle, and finally an outermost boundary region located principally in the dawn‐side magnetosphere which is associated with solar wind interaction and the Dungey‐cycle. The nature of the ionospheric flow and currents resulting from the combined action of these processes is outlined. In particular, we point out that the region of open field lines associated with the Dungey‐cycle should be a region of near‐stagnation in the ionosphere in the rest frame of the dipole, compared with surrounding regions of few‐km s−1 sub‐corotational flow.