bluuebunny/crossref_metadata_2025 huggingface dataset:
A statistical comparison of the AMIE derived and DMSP‐SSIES observed high‐latitude ionospheric electric field
Authors: Kihn E. A. , Redmon R. , Ridley A. J. , Hairston M. R.
Published: August 2006

The ion drift velocities and electric field derived from the Assimilative Mapping of Ionospheric Electrodynamics technique (AMIE) are compared with the same parameters observed by the Defense Meteorological Satellite Program's (DMSP) Special Sensor–Ions, Electrons, and Scintillation (SSIES) instrument. In addition the along‐track cross polar cap potential, the correlation between the curves, and other metrics are compared and those results are binned by various criteria. The criteria include spacecraft, year, season, and magnetic activity level. We observed a reasonable correlation between the AMIE results and DMSP data with respect to the along‐track potential, though the AMIE results tend to show a lower potential by some 30–50 percent, depending on spacecraft and orbit. Spacecraft in the same general orbits show similar relations with AMIE, implying that there is good intersatellite calibration for the DMSP array. There is a great deal of variability in the correlation, depending on season and activity level, and correlations with some of the spacecraft show a solar cycle dependance. It is further found that when we set a multifaceted criteria on each orbit for a DMSP‐AMIE match, including along‐track potential, Vy correlation, and peak potential locations, the results correspond between 35% and 55% for the dawn‐dusk spacecraft, while they only correspond 7%–12% of the time for noon‐midnight satellites.
Centennial increase in geomagnetic activity: Latitudinal differences and global estimates
Authors: Mursula K. , Martini D.
Published: August 2006

We study here the centennial change in geomagnetic activity using the newly proposed Inter‐Hour Variability (IHV) index. We correct the earlier estimates of the centennial increase by taking into account the effect of the change of the sampling of the magnetic field from one sample per hour to hourly means in the first years of the previous century. Since the IHV index is a variability index, the larger variability in the case of hourly sampling leads, without due correction, to excessively large values in the beginning of the century and an underestimated centennial increase. We discuss two ways to extract the necessary sampling calibration factors and show that they agree very well with each other. The effect of calibration is especially large at the midlatitude Cheltenham/Fredricksburg (CLH/FRD) station where the centennial increase changes from only 6% to 24% caused by calibration. Sampling calibration also leads to a larger centennial increase of global geomagnetic activity based on the IHV index. The results verify a significant centennial increase in global geomagnetic activity, in a qualitative agreement with the aa index, although a quantitative comparison is not warranted. We also find that the centennial increase has a rather strong and curious latitudinal dependence. It is largest at high latitudes. Quite unexpectedly, it is larger at low latitudes than at midlatitudes. These new findings indicate interesting long‐term changes in near‐Earth space. We also discuss possible internal and external causes for these observed differences. The centennial change of geomagnetic activity may be partly affected by changes in external conditions, partly by the secular decrease of the Earth's magnetic moment whose effect in near‐Earth space may be larger than estimated so far.
Microblock rotations and fault coupling in SE Asia triple junction (Sulawesi, Indonesia) from GPS and earthquake slip vector data
Authors: Socquet Anne , Simons Wim , Vigny Christophe , McCaffrey Robert , Subarya Cecep , Sarsito Dina , Ambrosius Boudewijn , Spakman Wim
Published: August 2006

The island of Sulawesi, eastern Indonesia, is located within the triple junction of the Australian, Philippine, and Sunda plates and accommodates the convergence of continental fragments with the Sunda margin. We quantify the kinematics of Sulawesi by modeling GPS velocities and earthquake slip vectors as a combination of rigid block rotations and elastic deformation around faults. We find that the deformation can be reasonably described by a small number of rapidly rotating crustal blocks. Relative to the Sunda Plate, the southwestern part of Sulawesi (Makassar Block) rotates anticlockwise at ∼1.4°/Myr. The northeastern part of Sulawesi, the Bangai‐Sula domain, comprises three blocks: the central North Sula Block moves toward the NNW and rotates clockwise at ∼2.5°/Myr, the northeastern Manado Block rotates clockwise at ∼3°/Myr about a nearby axis, and East Sulawesi is pinched between the North Sula and Makassar blocks. Along the boundary between the Makassar Block and the Sunda Plate, GPS measurements suggest that the trench accommodates ∼15 mm/yr of slip within the Makassar Strait with current elastic strain accumulation. The tectonic boundary between North Sula and Manado blocks is the Gorontalo Fault, moving right laterally at about 11 mm/yr and accumulating elastic strain. The 42 mm/yr relative motion between North Sula and Makassar blocks is accommodated on the Palu‐Koro left‐lateral strike‐slip fault zone. The data also indicate a pull‐apart structure in Palu area, where the fault shows a transtensive motion and may have a complex geometry involving several active strands. Sulawesi provides a primary example of how collision can be accommodated by crustal block rotation instead of mountain building.
Global gravity, bathymetry, and the distribution of submarine volcanism through space and time
Authors: Watts A. B. , Sandwell D. T. , Smith W. H. F. , Wessel P.
Published: August 2006

The seafloor is characterized by numerous seamounts and oceanic islands which are mainly volcanic in origin. Relatively few of these features (<∼0.1%), however, have been dated, and so little is known about their tectonic setting. One parameter that is sensitive to whether a seamount formed on, near, or far from a mid‐ocean ridge is the elastic thickness,Te, which is a proxy for the long‐term strength of the lithosphere. Most previous studies are based on using the bathymetry to calculate the gravity anomaly for different values ofTeand then comparing the calculated and observed gravity anomaly. The problem with such an approach is that bathymetry data are usually limited to single‐beam echo sounder data acquired along a ship track and these data are too sparse to define seamount shape. We therefore use the satellite‐derived gravity anomaly to predict the bathymetry for different values ofTe. By comparing the predicted bathymetry to actual shipboard soundings in the vicinity of each locality in the Wessel global seamount database, we have obtained 9758Teestimates from a wide range of submarine volcanic features in the Pacific, Indian, and Atlantic oceans. Comparisons where there are previous estimates show that bathymetric prediction is a robust way to estimateTeand its upper and lower bounds.Teat sites where there is both a sample and crustal age show considerable scatter, however, and there is no simple relationship betweenTeand age. Nevertheless, we are able to tentatively assign a tectonic setting to eachTeestimate. The most striking results are in the Pacific Ocean where a broad swath of “on‐ridge” volcanism extends from the Foundation seamounts and Ducie Island/Easter Island ridge in the southeast, across the equator, to the Shatsky and Hess rises in the northwest. Interspersed among the on‐ridge volcanism are “flank ridge” and “off‐ridge” features. The Indian and Atlantic oceans also show a mix of tectonic settings. Off‐ridge volcanism dominates in the eastern North Atlantic and northeast Indian oceans, while flank ridge volcanism dominates the northeastern Indian and western south Atlantic oceans. We have been unable to assign the flank ridge and off‐ridge estimates an age, but the on‐ridge estimates generally reflect, we believe, the age of the underlying oceanic crust. We estimate the volume of on‐ridge volcanism to be ∼1.1 × 106km3which implies a mean seamount addition rate of ∼0.007 km3yr−1. Rates appear to have varied through geological time, reaching their peak during the Late/Early Cretaceous and then declining to the present‐day.
Circulation along the Mexican Caribbean coast
Authors: Cetina P. , Candela J. , Sheinbaum J. , Ochoa J. , Badan A.
Published: August 2006

Data from an array of seven subsurface upward‐looking moored Acoustic Doppler Current Profilers (ADCPs) and four subsurface pressure sensors deployed from August 2002 to August 2003 along the Caribbean coast of Mexico showed that the currents in the area have a predominant northeastward direction along the coast, are coherent within the upper 130 m of the water column, and have a general tendency to increase northward, reaching magnitudes of 2.4 m/s north of Cozumel. In addition, important weeklong reversal periods (southward flows) are observed around Chinchorro Bank. A vertical current profile EOF analysis at each station indicates high coherence within the study area, with the first vertical mode at each station explaining at least 69% of variance and current vectors aligned with the coast. A second EOF analysis carried out for any uniform depth level using current data from all stations shows high coherence in the horizontal as well. The first mode explains at least 59% of the variance and has a dominant 3‐month‐long variability. Comparison between the current patterns along the Mexican Caribbean coast and in the Yucatan Channel suggests that dynamics of the entire area might be strongly influenced by the passage of eddies through the region. Comparison of a Singular Spectral Analysis (SSA) of the principal components of currents with the pressure difference across the channels supports the idea of eddies modulating current variability. Numerical model results indicate that high values of the current intensity indexes are associated with eddies. The flow along Chinchorro and Cozumel channels is in geostrophic balance most of the observation time, but with week‐long ageostrophic periods which are predominant off Cozumel. These events appear to occur when eddies are traversing the region.
Smart balloon observations over the North Atlantic: O3 data analysis and modeling
Authors: Mao Huiting , Talbot Robert , Troop Donald , Johnson Randy , Businger Steven , Thompson Anne M.
Published: August 2006

The temporal and spatial variations of ozone (O3) in polluted continental outflow over the North Atlantic were investigated during the International Consortium for Atmospheric Research on Transport and Transformation (ICARTT) field campaign in July–August 2004. Our analysis utilized measurements of O3 from three smart balloons traveling at 0.5–3 km altitude in combination with simulations using the MM5/SMOKE/CMAQ air quality modeling system. Model results for over and within 300 km off North America were corroborated by comparison to a suite of measurements from ground stations, ozonesondes, and the NOAA ship Ronald H. Brown cruising in the Gulf of Maine. A prominent feature of the O3 distribution was the high mixing ratios over the North Atlantic, reaching a peak value of 171 ppbv, compared to the northeastern United States (<∼100 ppbv). The enhanced O3 levels over ocean, mostly observed at night, appeared to be the result of four factors: (1) a supply of precursors in prevailing flow off the polluted U.S. east coast, (2) significant daytime in situ chemical production, (3) minimal depositional loss to the ocean at the balloon altitudes, and (4) small nighttime chemical loss. An important implication is that quantification of O3 export from the United States must include estimation of downwind chemical processing in polluted air masses. Balloons 3 and 4 were launched within 18 hours of each other, and their tracks allowed examination of horizontal gradients in O3 across distances varying from 200 to 400 km. In air masses influenced by recent outflow (<2 days) the O3 gradient was −0.2 to 0.2 ppbv km−1, while by distant source regions (>2 days) it exhibited only −0.05–0.05 ppbv km−1. These same two balloons encountered Hurricane Alex at different times, but both measured O3 mixing ratios >100 ppbv. Our model results show clearly that polluted air from the mid‐Atlantic states was channeled directly into Alex's inflow region. Overall, variations in O3 on timescales of tens of minutes to hours are attributed to its highly heterogeneous distribution in urban plumes, with variations over hours to days caused by changing source regions related to cyclonic activity.
Regolith thickness instability and the formation of tors in arid environments
Authors: Strudley Mark W. , Murray A. Brad , Haff Peter K.
Published: August 2006

We present model results suggesting that a physical erosion–bedrock weathering feedback is responsible for the development of isolated bedrock knobs (tors/inselbergs) that often punctuate otherwise smooth pediments of homogeneous basement lithology. Tors and larger, more heavily jointed and morphologically complex exposures, inselbergs, may arise as a consequence of fluctuations in rainfall and sediment transport conditions combined with a bedrock weathering mechanism that depends on regolith thickness. Hydrogeochemical considerations and field observations in arid, granitic environments suggest that the relationship between weathering rate and regolith thickness exhibits a maximum for a finite thickness of cover. We have encapsulated this simple erosion‐weathering feedback in a numerical model simulating arid/semiarid landscape evolution that produces low‐sloping pediments punctuated by tors. Tors form during periods of higher effective moisture, resulting in local base level incision and regolith thinning on pediments, invoking a transition in which mantled surfaces lower at rates exceeding the bare bedrock weathering rate. This condition favors the emergence and growth of tors in areas covered by regolith thickness less than a threshold value. Subsequent shifts in climate or local base level that restore sediment surface lowering rates less than the bare bedrock weathering rate will lead to a progressive decrease in tor height and, ultimately, their disappearance. Thus, according to this model, tors in arid environments represent possibly transient features related to fluctuations in climate or local transport conditions rather than palimpsests of an ancient landscape derived from differential subsurface weathering followed by regolith stripping.
Headwater stream temperature response to clear‐cut harvesting with different riparian treatments, coastal British Columbia, Canada
Authors: Gomi Takashi , Moore R. Dan , Dhakal Amod S.
Published: August 2006

A 6‐year study documented the effects of clear‐cut harvesting with and without riparian buffers (10 m and 30 m wide) on headwater stream temperature in coastal British Columbia. The experiment involved a replicated paired catchment design. Pretreatment calibration relations between the treatment and control streams were fitted using time series of daily minimum, mean, and maximum temperatures. Generalized least squares (GLS) regression was used to account for autocorrelation in the residuals. While water temperature in streams with 10 and 30 m buffers did not exhibit marked warming, daily maximum temperature in summer increased by up to 2°–8°C in the streams with no buffer. The effectiveness of the buffers may have been maximized by the north‐south orientation of the streams, which meant that the streams would be well shaded from late morning to early afternoon by the overhead canopy, even under the 10 m buffer. The variation in response for the no‐buffer treatments is consistent with the differences in channel morphology that influence their exposure to solar radiation and their depth. Relations between treatment effect and daily maximum air temperature suggested that recovery toward preharvest temperature conditions was occurring, with rates appearing to vary with stream and by season.
Integrating stakeholder values with multiple attributes to quantify watershed performance
Authors: Shriver Deborah M. , Randhir Timothy O.
Published: August 2006

Integrating stakeholder values into the process of quantifying impairment of ecosystem functions is an important aspect of watershed assessment and planning. This study develops a classification and prioritization model to assess potential impairment in watersheds. A systematic evaluation of a broad set of abiotic, biotic, and human indicators of watershed structure and function was used to identify the level of degradation at a subbasin scale. Agencies and communities can use the method to effectively target and allocate resources to areas of greatest restoration need. The watershed performance measure (WPM) developed in this study is composed of three major components: (1) hydrologic processes (water quantity and quality), (2) biodiversity at a species scale (core and priority habitat for rare and endangered species and species richness) and landscape scale (impacts of fragmentation), and (3) urban impacts as assessed in the built environment (effective impervious area) and population effects (densities and density of toxic waste sites). Simulation modeling using the Soil and Water Assessment Tool (SWAT), monitoring information, and spatial analysis with GIS were used to assess each criterion in developing this model. Weights for attributes of potential impairment were determined through the use of the attribute prioritization procedure with a panel of expert stakeholders. This procedure uses preselected attributes and corresponding stakeholder values and is data intensive. The model was applied to all subbasins of the Chicopee River Watershed of western Massachusetts, an area with a mixture of rural, heavily forested lands, suburban, and urbanized areas. Highly impaired subbasins in one community were identified using this methodology and evaluated for principal forms of degradation and potential restoration policies and BMPs. This attribute‐based prioritization method could be used in identifying baselines, prioritization policies, and adaptive community planning.
Investigating the applicability of end‐member mixing analysis (EMMA) across scale: A study of eight small, nested catchments in a temperate forested watershed
Authors: James April L. , Roulet Nigel T.
Published: August 2006

Current interest in multicatchment hydrologic studies challenges the use of geochemical mixing models across scale, where changes in stream water chemistry from catchment to catchment may indicate (1) changes in the proportional contributions of end‐members, (2) changes in the geochemical signatures of end‐members in space, or (3) changes in the geochemical signatures of end‐members in time. In this study we examine stream water chemistry from a series of eight nested catchments in a 1.47 km2 temperate forest watershed in southern Quebec for evidence of contributing end‐members. We use eigenvector and residual analysis (Hooper, 2003) of the multivariate stream water chemistry records to estimate the dimensionality of the mixing space for each individual catchment, indicating the number of contributing end‐members. Using the mixing space of the largest, highest‐order catchment (1.47 km2), we evaluate its ability to predict stream water chemistry in the seven upstream catchments, representing progressively smaller areas. We observe significant spatial variation in ionic mixing ratios within the 147 ha watershed. Only spatial testing across catchments allowed us to identify appropriate conservative tracers most compatible with the application of a single mixing model across scale. On the seasonal timescale, groundwater geochemistry changes significantly due to the recharge from spring snowmelt, indicating a mixture of two groundwater end‐members of varying age. On the timescale of storm events, shallow perched water and throughfall provide geochemical signatures consistent with physical mixing while unsaturated zone soil water sampled from local pockets of glacial till does not. Our results suggest cautious application of end‐member mixing analysis (EMMA) for multicatchment studies.
Modeling of long‐wave and net radiation energy distribution within a homogeneous plant canopy via multiple scattering processes
Authors: Zhao Wenguang , Qualls Russell J.
Published: August 2006

This paper presents a newly developed multiple‐layer, long‐wave radiation scattering model for use in homogeneous vegetation canopies. The model is able to simulate the radiation distribution within and the outgoing radiation above the canopy. This model differs from the shortwave model developed earlier by the authors owing to the complexity introduced by the fact that leaves within and soil below the canopy emit long‐wave radiation in accordance with their surface temperature. Combined, the short‐ and long‐wave models are able to simulate net radiation distribution above and within the canopy sublayers and at the soil surface. The model represents multiple scatterings of radiation reflected, transmitted, and emitted from leaf surfaces and penetrating through gaps as infinite series equations, which are reduced analytically to simple forms. In stand‐alone mode this model has the limitation that it requires canopy temperature profile data as input in order to simulate outgoing long‐wave radiation and net radiation. However, once we or other users couple this model to a turbulent transfer model, canopy temperature profiles will be produced as model output, making this a useful tool for remote sensing data assimilation. The model was tested against measurements collected in a wheat field in 2002. Satisfactory agreement was obtained between the modeled outgoing long‐wave radiation above a wheat canopy and observed long‐wave radiation measured with an Eppley precision infrared radiometer (PIR), both for daily total values and diurnal variation of 20‐min averages. The root‐mean‐square error (RMSE) of daily total values of outgoing long‐wave radiation, with respect to measurements, was only 1.1% of the mean of the measurements. Comparison of the modeled net radiation with two independent measurements produced RMSE values equal to 3.7% of the mean measured daily total net radiation.
Recent frequency component changes in interannual climate variability
Authors: Peel Murray C. , McMahon Thomas A.
Published: August 2006

The potential impact of climate change on the variability structure of climate has been investigated predominately through changes to extreme event frequency or the shape of the daily frequency distribution. Recent change to interannual climate variability has received less attention. Here we report that the interannual variability of temperature and precipitation has marginally decreased since 1970. However, within this marginal decrease the inter‐decadal component of interannual variability has decreased for both temperature and precipitation. The temperature results are consistent across urban and rural stations indicating that they are not due to any urbanisation effect.
Impact of tropical Pacific variability on the mean North Atlantic thermohaline circulation
Authors: Semenov Vladimir A. , Latif Mojib
Published: August 2006

A series of 500 years long coupled general circulation model simulations has been performed, in which the sea surface temperatures (SSTs) in different tropical oceans have been prescribed from climatology. A statistically significant reduction by about one Sverdrup of the meridional overturning circulation (MOC) in the North Atlantic was found when the tropical Pacific SSTs do not vary interannually. Anomalously low salinities originating in the tropical Atlantic due to increased precipitation drive the reduction of the MOC. Climatological SSTs in the tropical Pacific lead to a “La Niña”‐like state due to the nonlinear response of the atmosphere to SST anomalies. The shift of the mean atmospheric circulation in the tropical Pacific leads to a cyclonic anomaly over the eastern tropical Atlantic with a corresponding precipitation increase. The results suggest that changes in the SST variability of the tropical Pacific can drive changes in the mean state of remote regions.
Accelerated drawdown of meridional overturning in the late‐glacial Atlantic triggered by transient pre‐H event freshwater perturbation
Authors: Hall I. R. , Moran S. B. , Zahn R. , Knutz P. C. , Shen C.‐C. , Edwards R. L.
Published: August 2006

Abrupt decreases of the Atlantic meridional overturning circulation (MOC) during the Late Pleistocene have been directly linked to catastrophic discharges of glacimarine freshwater, triggering disruption of northward marine heat transport and causing global climate changes. Here we provide measurements of excess sedimentary 231Pa/230Th from a high‐accumulation sediment drift deposit in the NE Atlantic that record a sequence of sudden variations in the rate of MOC, associated deep ocean ventilation and surface‐ocean climatology. The data series reveal a sequential decrease in the MOC rate at ∼18.0 ka BP ago that coincides with only transient and localized freshwater inputs. This change represents a substantial, though not total, cessation in MOC that predates the major Heinrich (H1) meltwater event by at least 1,200 years. These results highlight the potential of targeted freshwater perturbations in promoting substantial MOC changes without a direct linking with catastrophic freshwater surges.
Aircraft measurements of cloud droplet spectral dispersion and implications for indirect aerosol radiative forcing
Authors: Zhao Chunsheng , Tie Xuexi , Brasseur Guy , Noone Kevin J. , Nakajima Teruyuki , Zhang Qiang , Zhang Renyi , Huang Mengyu , Duan Ying , Li Gelun , Ishizaka Yutaka
Published: August 2006

Using a large amount of aircraft measurements of cloud droplet size distributions, the relationship between cloud spectral relative dispersion (ɛ) and cloud droplet number concentration (Nc) is studied. The results indicate that the value of ɛ varies between 0.2 to 0.8 when the cloud droplet number concentration is low (about 50 cm−3), and converges toward a narrow range of 0.4 to 0.5 when the cloud number concentration is higher. Because the distribution of the cloud droplet size is an important parameter in estimating the first indirect radiative effect of aerosols on the climate system, the uncertainty in the corresponding radiative forcing can be reduced by 10–40% (depending on cloud droplet number density) under high aerosol loading. This finding is important for improving climate change projections, especially for the regions where aerosol loading is high and continues to increase.
Frictional heat from faulting of the 1999 Chi‐Chi, Taiwan earthquake
Authors: Tanaka H. , Chen W. M. , Wang C. Y. , Ma K. F. , Urata N. , Mori J. , Ando M.
Published: August 2006

The frictional heat generated during an earthquake is thought to be a major portion of the total energy release. However, there have been no direct measurements of the heat generated by a large earthquake. We present an estimate of the frictional heat produced by the 1999 Chi‐Chi, Taiwan earthquake (Mw 7.6), from temperature anomaly that is measured in a borehole penetrating a large slip region (∼10 m) of the fault. A local increase in the temperature profile across the fault is interpreted to be the residual heat generated during the earthquake. Analyses of this temperature anomaly lead to a low estimate of the dynamic shear stress, 0.5 to 0.9 MPa, and the heat produced in the large slip region of the fault, 0.68 to 1.32 × 1017 J. The total frictional energy is estimated as 2.4 to 6.1 × 1017 J, indicating that seismic efficiency is 1 to 3%.
MJO‐related summer cooling and phytoplankton blooms in the South China Sea in recent years
Authors: Isoguchi Osamu , Kawamura Hiroshi
Published: August 2006

The Madden‐Julian Oscillation (MJO) is a well known atmospheric phenomenon in the equatorial zone. We investigated interaction between the MJO and oceanic phenomena in the South China Sea (SCS). Sea surface temperature (SST) variability at 30–60 day periods is relatively strong off the South Vietnam coast in the central SCS. A cross‐wavelet analysis for the SST off the Vietnam coast and a MJO index reveal significant large covariance at 30–60 day periods in the summers of 2000–2002. Regressed maps of the SST and wind fields on the MJO index in these summers demonstrate that the intensification of southwesterly monsoon and resultant SST cooling occur with the MJO in the SCS. Chlorophyll‐a over the cooling center also oscillates in sync with the MJO and the cooling. It is thus found that the MJO‐related wind fields can induce the cooling and phytoplankton bloom off the South Vietnam coast in specific summers.
Antarctic temperatures over the past two centuries from ice cores
Authors: Schneider David P. , Steig Eric J. , van Ommen Tas D. , Dixon Daniel A. , Mayewski Paul A. , Jones Julie M. , Bitz Cecilia M.
Published: August 2006

We present a reconstruction of Antarctic mean surface temperatures over the past two centuries based on water stable isotope records from high‐resolution, precisely dated ice cores. Both instrumental and reconstructed temperatures indicate large interannual to decadal scale variability, with the dominant pattern being anti‐phase anomalies between the main Antarctic continent and the Antarctic Peninsula region. Comparative analysis of the instrumental Southern Hemisphere (SH) mean temperature record and the reconstruction suggests that at longer timescales, temperatures over the Antarctic continent vary in phase with the SH mean. Our reconstruction suggests that Antarctic temperatures have increased by about 0.2°C since the late nineteenth century. The variability and the long‐term trends are strongly modulated by the SH Annular Mode in the atmospheric circulation.
Cluster observations of broadband electromagnetic waves in and around a reconnection region in the Earth's magnetotail current sheet
Authors: Petkaki P. , Freeman M. P. , Walsh A. P.
Published: August 2006

We present an analysis of the electric and magnetic wave spectra on kinetic scales during several crossings of a reconnecting current sheet. The spectra were measured from 1 Hz or less up to 4096 Hz by the EFW, FGM and STAFF instruments onboard the Cluster spacecraft between 3 and 4 UT on 11 October 2001. During the event plasma flows of order of the local Alfvén speed reversed from tailward to earthward, suggesting that a reconnection site moved over the spacecraft. We ordered the observed electric and magnetic field wave spectrum by the position within the current sheet using the magnitude of the magnetic field B. We found that the electric and magnetic wave power decreased considerably at all frequencies towards the center of the current sheet (B ≈ 0 nT). The electric energy density decreases 5 orders of magnitude from the edge of the current sheet (B = 19 nT) to the center and the magnetic energy density peaks within the current sheet (B = 13 nT) and is decreased by 2.5 orders of magnitude at the center. Within the current sheet, the electric and magnetic wave spectra were dominantly broadband electromagnetic noise (i.e., power law spectra with exponents ≈−1.4 and ≈−2.4, respectively) throughout the frequency range ∼0.1–1000 Hz, spanning from MHD (i.e., ion cyclotron frequency ≈0.2 Hz) to almost the electron plasma frequency (≈4000 Hz). We argue that the wave activity is likely to be whistler wave turbulence and discuss the implications of these results for reconnection from wave‐particle interactions.
Coseismic slip distribution of the 2003 Mw 6.6 San Simeon earthquake, California, determined from GPS measurements and seismic waveform data
Authors: Rolandone F. , Dreger D. , Murray M. , Bürgmann R.
Published: August 2006

We combine geodetic and seismic data sets to constrain the coseismic slip distribution of the Mw6.6 San Simeon earthquake which occurred in the central California Coast Ranges on December 22, 2003. We use continuous and survey‐mode GPS observations along with seismic waveform data from the California Integrated Seismic Network (CISN). We invert both data sets for the distribution of finite fault slip in a layered‐Earth model. The inversion results indicate that the rupture extends to the southeast of the epicenter for approximately 25–30 km and occurred in a relatively shallow depth range between 1 to 10 km. The average and peak slip are 0.61 m and 2.37 m, respectively. The scalar seismic moment is 7.85e18 Nm, and the static stress drop 1.7 MPa. This thrust earthquake is characterized by its shallow, along‐strike extended slip.
Deep mantle origin of kimberlite magmas revealed by neon isotopes
Authors: Sumino Hirochika , Kaneoka Ichiro , Matsufuji Kyosuke , Sobolev Alexander V.
Published: August 2006

We measured noble gases in olivines extracted from alteration‐free samples of the Udachnaya‐East kimberlite pipe, eastern Siberia. Neon isotope ratios indicate that the kimberlite has a less nucleogenic Ne signature than a typical mid‐ocean ridge basalt (MORB) source, which is consistent with the less radiogenic 40Ar/36Ar ratio compared to MORB and subcontinental lithospheric mantle (SCLM) sources. Based on He‐Ne systematics, the 3He/4He ratio of the plume source of the Udachnaya kimberlite pipe would be higher than 15 RA with the dominant He signature of the magma acquired by assimilation of SCLM and/or crustal material during magma ascent. Our results indicate that the source of the Udachnaya kimberlite has similar noble gas characteristics to those of ocean island basalts (OIBs). Its origin is therefore deeper than that of the MORB source mantle, and probably is the same as the OIB‐source mantle.
Remote sensing of the solar site of interchange reconnection associated with the May 1997 magnetic cloud
Authors: Crooker N. U. , Webb D. F.
Published: August 2006

The direction of suprathermal electron flux on open magnetic field lines in the 15 May 1997 magnetic cloud is used to predict the solar location of the interchange reconnection that released one end of what presumably were doubly connected field lines in the coronal mass ejection (CME) of origin on 12 May. A search for an X‐ray signature of the interchange reconnection in the predicted location reveals a long‐lasting arched structure stretching from high above the CME site to the northern polar coronal hole. At the edge of the coronal hole, coincident with the X‐ray feature, are previously reported extreme ultraviolet brightenings (“crinkles”). The observations are consistent with a CME flux rope forming in a near‐quadrupolar configuration while overhead open field lines reconnect with the rising, closed, rope fields to open one leg of the rope loop. The pattern is similar to the breakout model except there are no closed overhead field lines through which the rising flux rope must break out. The near‐quadrupolar source appears to be responsible for the mismatch between the polarity of the flux rope observed at 1 AU and the sector in which it was embedded. Spacecraft interception of the leg rather than the apex of the flux rope loop may be responsible for the mismatch between the low inclination of the cloud axis and the high inclination predicted from the preexisting filament and magnetic configuration at the source.
Mathematical analysis of the wavelet method of chaos control
Authors: Shieh Shih-Feng , Wang Yiqian , Wei Guowei , Lai Choy-Heng
Published: August 2006

In this paper, we provide mathematical analysis for the controllability of chaos in wavelet subspaces. We prove that depending on the scale of the wavelet operation and the number of the coupled oscillators, the critical coupling strength for the occurrence of chaos synchronization becomes many times smaller if the original coupling matrix is appropriately treated with the wavelet transform. Moreover, we obtain rigorous relations connecting the critical values and the wavelet subspace operations. Our mathematical results are completely consistent with early numerical simulations.
Translational to rotational energy transfer in molecule-surface collisions
Authors: Ambaye Hailemariam , Manson J. R.
Published: August 2006

A theoretical approach that combines classical mechanics for treating translational and rotational degrees of freedom and quantum mechanics for describing the excitation of internal molecular modes is applied to the scattering of diatomic molecules from metal surfaces. Calculations are carried out for determining the extent of energy transfer to the rotational degrees of freedom of the projectile molecule. For the case of observed spectra of intensity versus final rotational energy, quantitative agreement with available experimental data for the scattering of NO and N2 from close packed metal surfaces is obtained. It is shown that such measurements can be used to determine the average rotational energy of the incident molecular beam. Measurements of the exchange of energy between translational and rotational degrees of freedom upon collision are also described by calculations for these same systems.
Relationship between edge drift and atomic migration during electromigration of eutectic SnPb lines
Authors: Yoon Min-Seung , Lee Shin-Bok , Kim Oh-Han , Park Young-Bae , Joo Young-Chang
Published: August 2006

The existence of an incubation stage before edge drift occurs was found by examining the electromigration characteristics of eutectic SnPb solder in an edge drift structure using in situ scanning electron microscopy and the interruptive test method. During this incubation stage, the depletion of Pb was observed at the cathode end. From the change in resistance, the activation energies for the incubation and edge movement stages were calculated to be 0.88 and 1.02eV, respectively. Based on a comparison of the activation energies for each stage with the previously reported values, it is believed that, during the incubation stage, Pb migrated before Sn and that the edge movement resulted from the migration of Sn. These results suggest that Pb depletion is a prerequisite for electromigration-induced void nucleation in eutectic SnPb solder.
Real-time x-ray observation of solidification from undercooled Si melt
Authors: Nagashio K. , Adachi M. , Higuchi K. , Mizuno A. , Watanabe M. , Kuribayashi K. , Katayama Y.
Published: August 2006

Grain refined microstructure is often obtained spontaneously in the solidification of metals and semiconductors from the undercooled melt without any external forces. Although it has been reported that the grain refinement is mainly caused by the fragmentation of the dendrites, the dynamic process of the fragmentation of dendrites has not been fully understood because only the microstructure after the solidification has been analyzed. Here, we present a time-resolved two-dimensional x-ray diffraction experiment on the solidification of Si from the undercooled melt. The number of diffraction spots observed at low undercoolings (ΔT<100K) did not increase at the plateau stage, while the diffraction pattern at medium undercoolings (100K<ΔT<200K) changed from the spots with the tail to rings with the lapse of time. Both this result and high speed video imaging suggested that the high-order arms of the dendrites mostly detached from the main stems because nucleation could not be expected at the melting point after recalescence. The several spots observed at low undercoolings drastically changed to rings at high undercoolings (ΔT>200K), which indicated the complete fragmentation of dendrite main stem as well as high-order arms. This complete fragmentation resulted in the grain refined microstructure.
Dependence of charge buildup in the polyimide on the incident electron energy
Authors: Mahapatra S. K. , Dhole S. D. , Bhoraskar V. N. , Raju Gorur G.
Published: August 2006

Elemental silver was diffused in a number of polyimide (C22H10N2O5, PMDA-ODA, Kapton-H) samples using the developed method of 6MeV electron irradiation. The virgin and the silver diffused polyimide samples, each of dimension 12×12×25μm, were irradiated with electrons of different energies, varying from 2to20keV. Each sample was irradiated with single energy electrons for a period of 300s, at a current density of ∼50nA∕cm2. The variations in the sample current and the backscattered electron current with the irradiation period were studied. The gaseous species evolved from the polyimide during electron irradiation were investigated by a quadrupole mass spectrometer. The negative charge stored and the surface potential developed in the polyimide increased with increasing electron energy, even though the irradiation period and the incident electron current were kept constant. This phenomenon is attributed to the decrease in the number of the backscattered electrons and the increase in the number of charged gaseous species that evolved from the polyimide surface with increasing energy of the incident electrons. For the same electron energy and fluence, the charge stored in the silver diffused polyimide was lower than that developed in the virgin polyimide. This property of the silver diffused polyimide is desirable for the space applications.
A dipole interaction model for magnetochiral birefringence
Authors: Ruchon T. , Vallet M. , Chauvat D. , Le Floch A.
Published: August 2006

We have developed a classical model to investigate the magnetochiral birefringence of an isotropic chiral medium submitted to a longitudinal magnetic field. This model, which is an extension of the atom dipole interaction model, yields direct calculations from the polarizabilities and positions of the atoms of the considered molecules. The numerical values obtained for the magnetochiral birefringence, as well as for the optical activity and Faraday rotation, are supported by the previously published experimental results on limonene, proline, and tartaric acid.
The effect of x-ray, γ-ray, and UV radiations on the optical properties of RbCdF3:Mn2+
Authors: Dotzler C. , Williams G. V. M. , Edgar A. , Schweizer S. , Henke B. , Spaeth J. M. , Bittar A. , Hamlin J. , Dunford C.
Published: August 2006

We report the results of optical transmission, photoluminescence (PL), and radio-luminescence measurements on x ray, γ ray, and UV irradiated RbCdF3:Mn2+ single crystals with different Mn2+ concentrations. There is a radiation-induced increase in the optical absorption and PL intensity that correlates with the Mn2+ concentration. This suggests that the defect center that gives rise to the observed effect is associated with the Mn2+ ions. We propose that the defect center is an F-center where an electron is trapped at a fluorine vacancy situated near but not adjacent to the Mn2+ site. The PL intensity for UV (240–270nm), x-ray (<40keV), or γ-ray (60keV) irradiation saturates at high irradiation intensities, which can be attributed to a fixed concentration of defect sites determined by the Mn2+ concentration. We show that the radiation-induced PL intensity is correlated with the UV, x-ray, and Am241 γ-ray dose. This indicates that RbCdF3:Mn2+ has potential as a radiation dosimeter material.
Formation of waveguides in LiNbO3 by 6.0MeV F3+ implantation
Authors: Jia Chuan-Lei , Jiang Yi , Wang Xue-Lin , Chen Feng , Wang Lei , Jiao Yang , Wang Ke-Ming , Lu Fei , Shen Ding-Yu , Ma Hong-Ji , Nie Rui
Published: August 2006

6.0 MeV  F3+ ions are implanted into x-cut LiNbO3 crystals in doses ranging from 3.0×1013to1.0×1015ions∕cm2 at room temperature. Planar waveguide formations are confirmed and dark modes are measured by prism coupling technique with a wavelength of 633nm. TE modes due to both raised extraordinary index and barrier-confined waveguides are demonstrated. The Rutherford backscattering∕channeling technique is used to investigate the damage produced by implantation. The experimental results are analyzed. With a fiber probe technique, the waveguide loss from TE0 mode in sample implanted with the dose of 1.0×1014ions∕cm2 is measured which is about 0.76dB∕cm after annealing.
Multiscale modeling of fluid turbulence and flocculation in fiber suspensions
Authors: Jafari Arezou , Zamankhan Piroz , Mousavi S. Mohammad , Henttinen Krista
Published: August 2006

A mathematically rigorous, multiscale modeling methodology capable of coupling behaviors from the Kolmogorov turbulence scale through the full scale system in which a fiber suspension is flowing is presented. Here the key aspect is adaptive hierarchical modeling. Numerical results are presented focus of which are on fiber floc formation and destruction by hydrodynamic forces in turbulent flows. Specific consideration was given to molecular-dynamics simulations of viscoelastic fibers in which the fluid flow is predicted by a method which is a hybrid between direct numerical simulations and large eddy simulation techniques, and fluid fibrous structure interactions were taken into account. The present results may elucidate the physics behind the breakup of a fiber floc, opening the possibility for developing a meaningful numerical model of the fiber flow at the continuum level where an Eulerian multiphase flow model can be developed for industrial use.
A note on chaotic unimodal maps and applications
Authors: Zhou C. T. , He X. T. , Yu M. Y. , Chew L. Y. , Wang X. G.
Published: August 2006

Based on the word-lift technique of symbolic dynamics of one-dimensional unimodal maps, we investigate the relation between chaotic kneading sequences and linear maximum-length shift-register sequences. Theoretical and numerical evidence that the set of the maximum-length shift-register sequences is a subset of the set of the universal sequence of one-dimensional chaotic unimodal maps is given. By stabilizing unstable periodic orbits on superstable periodic orbits, we also develop techniques to control the generation of long binary sequences.
R
-leaping: Accelerating the stochastic simulation algorithm by reaction leaps
Authors: Auger Anne , Chatelain Philippe , Koumoutsakos Petros
Published: August 2006

A novel algorithm is proposed for the acceleration of the exact stochastic simulation algorithm by a predefined number of reaction firings (R-leaping) that may occur across several reaction channels. In the present approach, the numbers of reaction firings are correlated binomial distributions and the sampling procedure is independent of any permutation of the reaction channels. This enables the algorithm to efficiently handle large systems with disparate rates, providing substantial computational savings in certain cases. Several mechanisms for controlling the accuracy and the appearance of negative species are described. The advantages and drawbacks of R-leaping are assessed by simulations on a number of benchmark problems and the results are discussed in comparison with established methods.
A frequency domain laser based ultrasonic system for time resolved measurement of broadband acoustic transients
Authors: Balogun O. , Murray T. W.
Published: August 2006

A high-sensitivity frequency domain laser based ultrasonic system is presented which uses a low power, amplitude modulated continuous wave (cw) laser source for acoustic wave generation. The acoustic signals are detected using a path stabilized Michelson interferometer coupled to a rf lock-in amplifier. The modulation frequency of the generation laser is scanned over the bandwidth of interest, and transient acoustic signals are reconstructed from the frequency domain data. The effects of measurement frequency resolution, bandwidth, and time domain aliasing on the reconstructed transient response are discussed. Experimental results on thin plates, where diffuse acoustic wave fields lasting several hundred microseconds are seen as a result of multiple reflections off of sample boundaries, demonstrate that the time domain signal can be unambiguously reconstructed through appropriate selection of frequency resolution. Time domain reconstructions of acoustic signals over a bandwidth of 200MHz demonstrate the utility of the approach for acoustic microscopy; individual acoustic transients can be detected with extremely high signal to noise ratio and time gated for analysis.