bluuebunny/crossref_metadata_2025 huggingface dataset:
Bottom water renewal in the Santa Barbara Basin
Authors: Bograd Steven J. , Schwing Franklin B. , Castro Carmen G. , Timothy David A.
Published: December 2002

We use quarterly full water depth occupations of a station at the center of the Santa Barbara Basin to estimate the timing, frequency, and magnitude of basin renewal events over the period 1986–2000. Of 58 occupations we have identified 11 events (in 11 of the 15 years) that are highly suggestive of recent bottom water renewal, with periods of annual flushing interspersed with relatively stagnant periods. All but one of these events occurred in winter or spring, with the spring events having the largest changes in bottom water properties (cooling and oxygenation). The event recorded in April 1998, during a period of rapid transition from El Niño‐influenced to La Niña‐influenced local conditions, revealed the potential magnitude of a full basin flushing: an increase in bottom water oxygen content of more than 0.4 mL/L and a cooling of nearly half a degree over 2 months. Water property profiles and near‐surface circulation patterns suggest that sufficiently dense water at the western sill, combined with strong flow into the basin from the northwest, may be key prerequisites to renewal. Interannual variability in the strength, duration, and timing of coastal upwelling and in regional circulation and hydrography, forced largely by the local impact of El Niño events, modulates the flushing potential of the basin. The Santa Barbara Basin apparently does not get flushed every year, and renewal events are not restricted to winter‐spring. Since the frequency and intensity of basin renewal events can greatly impact local denitrification rates, benthic community structure, and underlying sedimentary processes, we recommend that paleoceanographic interpretations of the local sediment record take account of this seasonally and interannually varying cycle of bottom water renewal.
Evaluating the relationship between AVIRIS water vapor and poplar plantation evapotranspiration
Authors: Ogunjemiyo Segun , Roberts Dar A. , Keightley Keir , Ustin Susan L. , Hinckley Tom , Lamb Brian
Published: December 2002

Remotely sensed data acquired using the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) at two irrigated hybrid poplar plantation sites located in Oregon and Washington States were used to assess the feasibility of using AVIRIS retrieved column water vapor as a measure of evapotranspiration (ET) of poplar plantations. AVIRIS data collected on four different days in the summers of 1996, 1997 and 1998 were used to derive column water vapor over the sites. To relate column water vapor to poplar ET, we developed a hypothesis, which was used to infer the relationship between the two variables. The approach tested consisted of delineating homogenous vegetated patches and averaging the column water vapor to determine the downwind spatial distribution pattern (trend) in the water vapor signal. The results indicate that the poplars were transpiring at rates characteristic of vegetation under unlimited soil moisture conditions and that the vertical distribution of water vapor was chiefly driven by forced convection. The concentration and the observed trends in the column of water vapor over the vegetated patches were related to the moisture condition of the land cover upwind of their location, and the trends were best described by linear or quadratic functions. To give an idea of the strength of moisture flux in the AVIRIS vapor signal, latent heat fluxes were estimated, based on the slope of the trends. Comparison of the AVIRIS values with flux estimates at the Boardman site lend credence to the potential for AVIRIS retrieved column water vapor in fields such as ecology, agriculture and meteorology.
Modeling soil thermal and carbon dynamics of a fire chronosequence in interior Alaska
Authors: Zhuang Q. , McGuire A. D. , O'Neill K. P. , Harden J. W. , Romanovsky V. E. , Yarie J.
Published: December 2002

In this study, the dynamics of soil thermal, hydrologic, and ecosystem processes were coupled to project how the carbon budgets of boreal forests will respond to changes in atmospheric CO2, climate, and fire disturbance. The ability of the model to simulate gross primary production and ecosystem respiration was verified for a mature black spruce ecosystem in Canada, the age‐dependent pattern of the simulated vegetation carbon was verified with inventory data on aboveground growth of Alaskan black spruce forests, and the model was applied to a postfire chronosequence in interior Alaska. The comparison between the simulated soil temperature and field‐based estimates during the growing season (May to September) of 1997 revealed that the model was able to accurately simulate monthly temperatures at 10 cm (R> 0.93) for control and burned stands of the fire chronosequence. Similarly, the simulated and field‐based estimates of soil respiration for control and burned stands were correlated (R= 0.84 and 0.74 for control and burned stands, respectively). The simulated and observed decadal to century‐scale dynamics of soil temperature and carbon dynamics, which are represented by mean monthly values of these variables during the growing season, were correlated among stands (R= 0.93 and 0.71 for soil temperature at 20‐ and 10‐cm depths,R= 0.95 and 0.91 for soil respiration and soil carbon, respectively). Sensitivity analyses indicate that along with differences in fire and climate history a number of other factors influence the response of carbon dynamics to fire disturbance. These factors include nitrogen fixation, the growth of moss, changes in the depth of the organic layer, soil drainage, and fire severity.
Charge transfer measurements during single ice crystal collisions with a target growing by riming
Authors: Pereyra Rodolfo G. , Avila Eldo E.
Published: December 2002

Direct measurements of the electric charge separated from individual collisions between vapor grown ice crystals and an artificial graupel growing by riming have been made in the present laboratory work. The measurements were performed with an impact velocity of 8.5 m s−1, the ambient temperature was varied in the range −5 to −20°C, the average ice crystal sizes between 20 to 40 μm, with an effective liquid water content up to 1.5 g m−3. The magnitude of the charge separated per collision is on the order of 10 fC, and the sign of the average charge depends on the ambient temperature for the present EW. We found that the artificial graupel charges positively for temperatures above −12°C and negatively for temperatures below −14°C. The current results are compared with those obtained by other authors that used the multiple crystal collision technique.
Interactions of mineral dust particles and clouds: Effects on precipitation and cloud optical properties
Authors: Yin Yan , Wurzler Sabine , Levin Zev , Reisin Tamir G.
Published: December 2002

Numerical simulations were performed to investigate the effect of cloud‐processed mineral dust particles on the subsequent development of cloud and precipitation and possible effects on cloud optical properties. A two‐dimensional (2‐D) nonhydrostatic cloud model with detailed microphysics was used. The initial aerosol spectra used in the 2‐D model consisted of both background cloud condensation nuclei and mineral dust particles. These were taken from the results of three successive runs of a parcel model that simulates the interaction of dust and sulfate particles with cloud drops and trace gases and then evaporates the cloud drops. The results show that insoluble mineral dust particles become effective cloud condensation nuclei (CCN) after passing through a convective cloud. Their effectiveness as CCN increases because of a layer of sulfate that is formed on their surface as they are first captured by growing drops or ice crystals and then released as these hydrometeors evaporate. Upon entering subsequent clouds, these particles increase the concentration of the activated drops and widen the drop size distribution. The present work shows that in continental clouds the effect of cloud‐processed dust particles is to accelerate the formation of precipitation particles, although the amount of precipitation depends on the concentration of the large and giant CCN. In maritime clouds the addition of cloud‐processed aerosol and mineral dust particles has a minimal effect on precipitation because the cloud starts with many large particles already. The addition of more CCN to either maritime or continental clouds increases their optical depth, even for those cases in which the precipitation amount is increased.
Study of atmospheric PCB concentrations over the eastern Mediterranean Sea
Authors: Mandalakis Manolis , Stephanou Euripides G.
Published: December 2002

Air samples were collected between April 1999 and March 2001 at a background marine site in the eastern Mediterranean Sea and analyzed for polychlorinated biphenyls (PCBs). The average concentrations of total PCB congeners (ΣPCBs) in the gas and particulate phases of the atmosphere were 68.1 ± 28.8 and 2.3 ± 1.8 pg/m3, respectively. The lack of seasonal variation for the atmospheric concentration of individual congeners and ΣPCBs and the shallow slopes obtained from the Clausius–Clapeyron (CC) plots for several PCB congeners indicated that long‐range transport is the main factor controlling the atmospheric levels of PCBs in this area. Most of the episodes with elevated concentrations of ΣPCBs concurred with air transport from western and central Europe. This observation was mostly attributed to the predominance of N‐NW winds in eastern Mediterranean. The wind speed apparently did not affect the atmospheric concentration of PCBs. Significant changes observed on the homologue group profile of PCBs were mostly related to the origin of air parcels sampled and during summer were most probably related to the reaction of the lighter congeners with OH radicals. Partitioning of PCBs between gas and particulate phases was well correlated with the subcooled liquid vapor pressure (PLo) for 11 of the 37 samples. The slopes of log Kp versus log PLo ranged between −0.233 and −0.445 and are among the shallowest measured worldwide. This fact may indicate absorption of PCBs in particles covered by a polar film.
Regional contrast in morning transitions observed during the 1999 Southern Oxidants Study Nashville/Middle Tennessee Intensive
Authors: White A. B. , Templeman B. D. , Angevine W. M. , Zamora R. J. , King C. W. , Russell C. A. , Banta R. M. , Brewer W. A. , Olszyna K. J.
Published: December 2002

This study investigates the impact of surface heterogeneity on the timing of the morning transitions observed during the 1999 Southern Oxidants Study Nashville/Middle Tennessee Intensive (SOS99N). The end of the morning transition occurs at a measurement site located in the Cumberland River Valley approximately 8 km northeast of downtown Nashville, on average, 1.25 h earlier than at three rural sites surrounding Nashville. This study shows that the early morning behavior of the boundary layers observed at the river valley site is dominated by local terrain features, whereas a previous study showed that the afternoon boundary layers observed at this site are more strongly influenced by its urban characteristics. Profiles of backscatter intensity recorded by monostatic sodars and Doppler wind profilers are analyzed to provide the evolution of boundary layer depth on days when a nocturnal inversion formed. These measurements indicate that the early morning growth rate of the convective boundary layer was faster, on average, at the river valley site in Nashville than at a rural, non‐river valley site where similar measurements were made (125 m h−1 versus 73 m h−1 from 0600 to 0800 h CST). A comparison of temperature profiles measured with radio acoustic sounding systems indicates that low‐level stability resulting from the nocturnal boundary layer had a stronger influence than surface energetics on the observed variations in boundary layer depth and morning transition end times. A single case study is shown to demonstrate the potential impact of the morning transition on gas phase chemistry measurements collected at a rural site. Case study and diurnally averaged time series show how surface‐layer humidity can be an effective tracer for diagnosing the end of the morning transition.
Simulating summertime rainfall variability in the North American monsoon region: The influence of convection and radiation parameterizations
Authors: Xu Jianjun , Small Eric E.
Published: December 2002

Studying the dynamics of the North American Monsoon System (NAMS) is essential for understanding and assessing the predictability of its variability. Limited‐area models are potentially useful tools for this endeavor, but it is important to first identify the suite of physical parameterizations that yields the most realistic simulations. We investigate how different convection and radiation schemes influence simulations of the NAMS produced with the MM5/OSU model. We focus on the simulated intraseasonal variability associated with monsoon onset (June to July) and changes between a wet (1999) and a dry (2000) year. We test six parameterizations, including two convection schema (Grell and Kain‐Fritsch) and three radiation schema (CCM2, Cloud, and RRTM). We compare results from 2‐month‐long simulations to observations of circulation (NCEP Reanalysis) and rainfall (CPC and CMAP). Differences in simulated rainfall produced by the various combinations of schema are substantial, and much greater than the differences that arise from internal model variability in a three‐member ensemble of Grell‐RRTM simulations. The Grell‐RRTM simulation produces the most realistic patterns and magnitudes of rainfall, including intraseasonal variations and the differences between the wet and dry year. Simulations using the Kain‐Fritsch scheme produce too much rainfall, and fail to represent the atypical, observed decrease in precipitation from June‐to‐July in 2000. The CCM2 radiation scheme produces a simulated climate that is too cloudy, yielding little rainfall in the NAMS region regardless of the convection scheme used. The Cloud and RRTM radiation schemes allow for feedbacks between condensation and the water content of clouds, which yields substantial improvements in the model simulations.
Iron abundances on the lunar surface as measured by the Lunar Prospector gamma‐ray and neutron spectrometers
Authors: Lawrence D. J. , Feldman W. C. , Elphic R. C. , Little R. C. , Prettyman T. H. , Maurice S. , Lucey P. G. , Binder A. B.
Published: December 2002

Global measurements of iron abundances on the lunar surface are presented using data from the Lunar Prospector (LP) Gamma‐Ray Spectrometer (GRS) and Neutron Spectrometer (NS). In this study, we derive relative iron abundances from the low‐altitude, high spatial resolution (∼(45 km)2) LP data using the 7.6 MeV neutron capture gamma‐ray doublet. As part of the LP‐GRS analysis, we demonstrate the importance of accounting for variations in neutron number density across the lunar surface by measuring neutron fluxes using LP‐NS data. In a first step of comparing the LP‐GRS data with previously published iron abundances inferred from Clementine Spectral Reflectance (CSR) data, we show that the existing CSR FeO data are nonlinear with respect to the LP relative iron abundances. We use the LP data to linearize the relationship between the CSR and the relative iron values then recalibrate the CSR data to iron abundance using returned soil abundances. We then correlate the CSR data, except for major anomalies, with the LP relative iron measurements to convert the LP data to absolute iron abundances. When we compare the LP‐GRS and revised CSR data sets, we find a very good correspondence. There are two locations (Mare Tranquillitatis and South Pole‐Aitken (SPA) basin) that show major discrepancies, suggesting that the CSR data are locally overestimating iron abundances. In both these regions, the discrepancies identified by the LP‐GRS/CSR comparison are possibly explained by mineralogical differences that are not accounted for in the CSR to FeO calibration. In regards to our understanding of the Moon, the LP data have found the following: (1) There exist large expanses of mare basalt in the western mare regions that have very high iron abundances (22–23 wt.% FeO) that are underrepresented but not absent from the returned sample collection and are highly unusual for mare soils, which typically contain a significant amount of highlands contamination. (2) The low iron abundances in the lunar highlands (∼5 FeO wt.%) are consistent with a previous analysis using thermal and epithermal neutrons and with the idea that the lunar crust formed by a relatively simple magma ocean process. (3) The comparison of LP and CSR derived iron abundances suggests that the material within SPA basin is similar to a norite‐type rock without an enriched mantle FeO signature. (4) A comparison of LP and CSR data at Tycho Crater shows a large discrepancy such that the CSR data show moderate iron abundances of 8–9 wt.% FeO while the LP data show very low iron abundances of 3–4 wt.% FeO. This discrepancy cannot yet be easily explained by any known process.
Inference on the nature and the mass of Earth's late veneer from noble metals and gases
Authors: Dauphas Nicolas , Marty Bernard
Published: December 2002

Noble metals and gases are very sensitive to the late accretion to the Earth of asteroids and comets. We present mass balance arguments based on these elements that indicate that 0.7 − 2.7 × 1022 kg of extraterrestrial bodies struck the Earth after core formation and that comets comprised less than 10−3 by mass of the impacting population. These results imply that the dynamics of asteroids and comets changed with time and that biogenic elements and prebiotic molecules were not delivered to the Earth by comets but rather by carbonaceous asteroids.
On novel developments of controlled evolution of level sets in the field of inverse shape problems
Authors: Ramananjaona C. , Lambert M. , Lesselier D. , Zolésio J.‐P.
Published: December 2002

Novel developments of the so‐called controlled evolution of level sets [Ramananjaona et al., 2001b], which is devoted to shape identification of homogeneous scattering obstacles buried in a known space from time‐harmonic wave field data, are considered herein. The emphasis is twofold: regularization of the geometry of the sought shape—enforced via a speed of motion of the level set in (pseudo)time and space resulting from the minimization of a properly penalized objective functional; and improvement of the convergence of the scheme itself by a choice of a time step adapted to the evolution of the level set and to the sought decrease of the objective functional. Key elements of the theoretical analysis are given, and several numerical examples illustrate pros and cons.
Extending records of the isotopic composition of atmospheric N2O back to 1800 A.D. from air trapped in snow at the South Pole and the Greenland Ice Sheet Project II ice core
Authors: Sowers Todd , Rodebaugh Amy , Yoshida Naohiro , Toyoda Sakae
Published: December 2002

A historical record of changes in the N2O isotope composition is important for a better understanding of the biogeochemical cycles involving atmospheric N2O. Here we combine measurements of trapped gases in the Greenland Ice Sheet Project II (GISP II) ice core and the interstitial air from the snowpack at the South Pole to reconstruct atmospheric N2O isotope records back to 1785 A.D. Results from six measurements of ice with gas ages between 1785 and 1819 A.D. indicate that the δ15N and δ18O of atmospheric N2O was 10.1 ± 0.6 and 47.4 ± 1.0‰, respectively. These values are 1.9 and 2.9‰ higher than present‐day values as measured in this study. A simple two‐box atmospheric model was constructed to simulate the various sources and sinks of atmospheric N2O over the last 250 years. Model results suggest that the total anthropogenic N2O emissions in 1995 were between 4.2 and 5.7 Tg N yr−1. The ice core and box model results were compared to δ15N and δ18O measurements of air trapped in the snowpack at South Pole spanning the 20th century. Our results suggest that δ15N and δ18O of atmospheric N2O have dropped by 1.7 and 0.9‰, respectively, during the last century. These data support previous predictions of decreasing atmospheric isotope ratios that are related to a ∼30% increase in total N2O emissions which are primarily related to agricultural activities.
Influence of bacterial uptake on deep‐ocean dissolved organic carbon
Authors: Bendtsen Jørgen , Lundsgaard Claus , Middelboe Mathias , Archer David
Published: December 2002

Particulate organic carbon (POC) sinking out of the sunlit euphotic zone at the surface of the ocean feeds the deep sea and alters the CO2 concentration of the atmosphere. Most of the sinking POC is reoxidized to dissolved inorganic carbon (DIC) before it hits the sea floor, but the mechanism for this is poorly understood. Here we develop a global model of the microbial loop in the aphotic zone based on new measurements of deep ocean bacterial metabolism. These together imply that a significant fraction of the decreasing POC flux with depth is converted to dissolved organic carbon (DOC) rather than directly to DIC as is commonly assumed, thereby providing the substrate for free‐living bacteria in the deep ocean. The model suggests the existence of a substantial DOC‐pool with a relatively fast turnover time in the deep sea. By implementing the microbial loop in a model of the global ocean circulation, we show that the observed gradient of DOC in the deep North Atlantic can be explained by the temperature dependence of bacterial metabolic activity in conjunction with the formation of deep‐water at high latitudes.
Millennial climate oscillations in NE Pacific surface waters over the last 82 kyr: New evidence from alkenones
Authors: Seki Osamu , Ishiwatari Ryoshi , Matsumoto Kohei
Published: December 2002

A climate instability in the last glacial, corresponding to Dansgaard‐Oeschger (D‐O) events, has been already recognized in the California margin in northeast Pacific. Detailed sea surface temperature (SST) changes in this region, however, have not been so far well elucidated. Here we report estimates of alkenone‐derived SSTs with the DO‐time scale from ODP Hole 1017E, off Point Conception, over the last 80 kyr. Our results show that alkenone SSTs clearly record D‐O and Heinrich Events. We also found that alkenone‐SSTs during 82‐58 ka and 18‐15 ka were considerably higher, and those in 15‐12 ka were lower than those derived from δ18O of planktonic foraminifera. These results appear to reflect fluctuations of water masses.
Depth‐varying constitutive properties observed in an isothermal glacier
Authors: Marshall H. P. , Harper J. T. , Pfeffer W. T. , Humphrey N. F.
Published: December 2002

Detailed three‐dimensional in‐situ measurements of deformation at depth are used to examine the rheology of a 6 × 106 m3 block of temperate glacier ice. Assuming that the viscosity of this ice is primarily dependent on stress, the relationship between inferred stress and measurements of strain‐rate above ∼115 m depth suggest a constitutive relationship with a stress exponent n ∼ 1. Deformation below 115 m is described by a non‐linear flow law with a power exponent of approximately 3–4. A sharp transition between the two flow regimes is likely caused by a change in the dominant mechanism from superplastic flow, basal slip, and/or diffusional flow near the surface to dislocation and intragranular deformation at depth.
Lightning activity during the 1999 Superior derecho
Authors: Price Colin G. , Murphy Brian P.
Published: December 2002

On 4 July 1999, a severe convective windstorm, known as a derecho, caused extensive damage to forested regions along the United States/Canada border, west of Lake Superior. There were 665,000 acres of forest destroyed in the Boundary Waters Canoe Area Wilderness (BWCAW) in Minnesota and Quetico Provincial Park in Canada, with approximately 12.5 million trees blown down. This storm resulted in additional severe weather before and after the occurrence of the derecho, with continuous cloud‐to‐ground (CG) lightning occurring for more than 34 hours during its path across North America. At the time of the derecho the percentage of positive cloud‐to‐ground (+CG) lightning measured by the Canadian Lightning Detection Network (CLDN) was greater than 70% for more than three hours, with peak values reaching 97% positive CG lightning. Such high ratios of +CG are rare, and may be useful indicators of severe weather.
Spatial distribution of lateral heterogeneity in the upper mantle around the western Pacific region as inferred from analysis of transverse components of teleseismic P‐coda
Authors: Nishimura Takeshi , Yoshimoto Kazuo , Ohtaki Toshiki , Kanjo Kenji , Purwana Ibnu
Published: December 2002

We investigated the spatial distribution of lateral heterogeneity in the upper mantle in the western Pacific region analyzing transverse components of teleseismic P‐coda recorded by broad‐band seismic networks. Large amplitude transverse components are observed at stations close to plate boundaries such as island arcs for the frequency range of 0.04–2.56 Hz, while small amplitudes are observed at stations on stable continents. Our envelope inversion applied to the observed P‐coda reveals large scattering coefficients at depths from 100 to more than 300 km beneath the island arcs, which are interpreted as strong heterogeneities originating from subducting slabs and mantle diapirs. Analyses of a dense seismic network further show a significant difference of heterogeneity between East and West Japan: the former is more heterogeneous than the latter. In contrasts, scattering coefficients less than 20% of the maximum beneath the island arcs are obtained beneath the stable continents, which represents homogeneous and transparent upper mantle.
Surface drifter pathways originating in the equatorial Atlantic cold tongue
Authors: Grodsky Semyon A. , Carton James A.
Published: December 2002

Subtropical cells (STCs) connect subduction zones of the eastern subtropics of both hemispheres to the equatorial current systems via equatorward flow in the thermocline. Some of this thermocline water is converted back into warm near‐surface water in the eastern equatorial cold tongue from whence it is exported poleward. Here we examine the export pathways from the cold tongue in the Atlantic based on recently available near‐surface drifter data. We find that, similar to its Pacific counterpart, water upwelled in the Atlantic cold tongue follows multiple pathways back into the subtropics, but not directly to the subduction zones. Thus the subtropical cells are open to extensive influence from, and exchange with, the subtropical and midlatitude ocean.
Coastal upwelling in a warmer future
Authors: Mote Philip W. , Mantua Nathan J.
Published: December 2002

Coastal upwelling helps set the physical context for marine ecosystems, and upwelling zones are among the most productive regions of the global ocean. Unlike earlier models, two state‐of‐the‐art climate models exhibit little change during the next century in the magnitude and seasonality of coastal upwelling, but climate models are still probably not sufficiently developed (for example, they underestimate interdecadal variability in upwelling) to provide valid projections of this key component of the coastal environment.
The effect of dynamics on the composition of Titan's upper atmosphere
Authors: Müller‐Wodarg I. C. F. , Yelle R. V.
Published: December 2002

Using a global time‐dependent general circulation model, we calculate the distribution of constituents in Titan's thermosphere resulting from transport caused by winds and molecular and eddy diffusion. Our simulations reveal that thermospheric winds effectively mix constituents in Titan's upper atmosphere. Consequently, the large eddy coefficients inferred from Voyager UVS observations may be a result of vigorous thermospheric circulation on Titan. Thermospheric winds also cause large diurnal variations in composition, with equatorial CH4 mole fractions near 1400 km ranging from ∼15% in the late afternoon to ∼58% in the early morning at equinox.
VLF, magnetic bay, and Pi2 substorm signatures at auroral and midlatitude ground stations
Authors: Smith A. J. , Freeman M. P. , Hunter S. , Milling D. K.
Published: December 2002

A superposed epoch analysis of 100–300 substorms is performed to determine the median size and shape of the substorm‐associated VLF chorus, magnetic bay, and Pi2 pulsation burst observed at the near‐auroral Halley research station, Antarctica, and at the midlatitude Faraday station at three different local times (2230, 2330, 0130 MLT). The spatial and temporal properties of the magnetic bay signatures are compared with the University of York implementation of the Kisabeth–Rostoker substorm current wedge (SCW) model and the Weimer pulse model, respectively. These constitute the best analytical models of the substorm to date. It is shown that the polarities and relative amplitudes of the observed magnetic bays in the H, D, and Z components at Halley at midnight MLT and at Faraday in the premidnight sector are consistent with the York model for a SCW 3 hours wide in MLT with its westward electrojet at 67°S magnetic latitude. In particular the little‐discussed Z component of the bay agrees with the model and is shown to be the clearest substorm signature of the three components, especially at midlatitude. The midnight and postmidnight bays are similar to the premidnight case but progressively smaller and cannot be fully reconciled with the model. The shape of the H and Z bays at Halley and the D bays at Faraday fit a normalized Weimer pulse well, with Weimer's 2 h−1 recovery rate, but the other components do not. The D component at Halley and H at Faraday do fit the Weimer pulse shape but with a faster recovery rate of 4 h−1. It is proposed that this is due to the effect of a decaying current in the SCW combining with the geometrical effect of changing SCW configuration and position relative to the observing station. The Z component at Faraday recovers more slowly than the 2 h−1 Weimer prediction; we cannot explain this. Secondary bays at Halley and Faraday show a clear tendency to recur after 2 hours. Inflection points just prior to onset at Halley and Faraday are argued to be related to reduced convection associated with northward turning of the IMF. The median substorm signature at Halley in the Pi2 frequency band (7–25 mHz) is well correlated with the bay structure, showing that it is part of a broader band, possibly turbulent, spectrum in the substorm‐dependent DP2 current. There is evidence of a minor additional narrow band component occurring at substorm onset. This is the dominant signal at Faraday which shows the classic midlatitude substorm signature, a short Pi2 pulsation burst at onset, that decreases progressively in intensity with increasing local time, implying a source region biased to the evening side or else preferred propagation to the east from a near‐midnight source.
Quiet time variability of the geosynchronous magnetic field and its response to the solar wind
Authors: Sanny J. , Tapia J. A. , Sibeck D. G. , Moldwin M. B.
Published: December 2002

We present a survey of the variability of the geosynchronous magnetic field strength on the dayside using observations by the GOES satellites over a period exceeding 4 years. Only intervals of reduced geomagnetic activity, as defined by Dst > −20 nT, were considered in this study. The magnetic field strength data were filtered with a passband of 1.7 mHz to 17 mHz (1–10 minutes), a process that eliminates the diurnal variation of the field strength and the effects of most of the higher frequency (>17 mHz) ultralow‐frequency (ULF) waves. The geosynchronous field strength appears to exhibit the greatest variability in the prenoon sector for spiral interplanetary magnetic fields (IMF) and in the postnoon sector for orthospiral IMF, suggesting that pressure pulses generated in the foreshock/bow shock region may have a significant influence on the geosynchronous field. The seasonal dependence of the variability was determined to be positively correlated to the seasonal dependence of ground‐based observations of magnetic impulse events. The response of the variability of the geosynchronous magnetic field strength around local noon to solar wind parameters was also studied. Here, we observed that the variability was strongly affected by changes in the solar wind dynamic pressure but was seemingly independent of the northward/southward direction of the interplanetary magnetic field. However, for high solar wind dynamic pressures, the variability was found to be greater for northward IMF than for southward IMF.
Capturing time and vertical variability of tropospheric ozone: A study using TES nadir retrievals
Authors: Bowman Kevin W. , Steck Tilman , Worden Helen M. , Worden John , Clough Shepard , Rodgers Clive
Published: December 2002

In this paper, the vertical resolution for Tropospheric Emission Spectrometer (TES) nadir ozone retrievals is established and is used to assess the ability of TES to capture time variations of ozone in the troposphere. This characterization is based on retrievals of ozone using simulated radiances generated from ozonesonde profiles taken over Bermuda from 14 April to 25 May 1993. To that end, a two‐step retrieval strategy that includes an initial estimate of the “shape” of the ozone followed by a finer‐resolution estimate was developed to provide rapid and robust convergence against large deviations of ozone profiles in the troposphere and lower stratosphere relative to a climatology. An error analysis is derived that accurately accounts for representation errors of the profile, choices of regularization, and the dependence of the retrieval error on both the statistics of the profile and spectral measurement noise, as well as the sensitivity of these retrievals to errors in temperature. This analysis shows that TES should be able to retrieve ozone in the nadir with an approximately 6 km resolution in the troposphere. The root‐mean square errors in estimates of the upper and lower tropospheric columns are about 1.35 Dobson units (DU) each. With this vertical resolution, TES would have the sensitivity to detect both the enhanced and reduced tropospheric ozone present in the Bermuda data set. Coupled with a 2‐day near‐repeat orbit and global coverage, TES retrievals of ozone could provide invaluable information to distinguish between anthropogenic and meteorological sources for the time variability of ozone in the troposphere.
Study of diurnal cycle of convective precipitation over Amazonia using a single column model
Authors: Betts Alan K. , Jakob Christian
Published: December 2002

The error in the diurnal cycle of precipitation over land in the tropics in the European Centre for Medium‐Range Weather Forecasts forecast model is investigated using a single column model with idealized forcing of the omega field, as well as short‐term and long runs of the full three‐dimensional model. The model precipitates a few hours after sunrise, as it does not represent correctly the morning development of a growing cumulus boundary layer. In the single column model, precipitation is closely linked to the mean forcing and surface evaporation, but the phase of diurnal varying omega forcing in relation to the diurnal solar cycle determines the relation of convective to large‐scale precipitation in the control model, as well as cloudiness and the net radiation balance. With diurnal subsidence peaking at midnight, but no mean ascent, the model shows a quasi 2‐day precipitation mode. With both strong mean ascent and diurnal forcing, ascent peaking in the daytime gave stratiform rain with large cloud cover and very low surface net radiation, while daytime subsidence and ascent at night gave strong daytime convective precipitation and high net radiation.
Ozone production efficiency in an urban area
Authors: Kleinman Lawrence I. , Daum Peter H. , Lee Yin‐Nan , Nunnermacker Linda J. , Springston Stephen R. , Weinstein‐Lloyd Judith , Rudolph Jochen
Published: December 2002

Ozone production efficiency can be defined as the number of molecules of oxidant (O3 + NO2) produced photochemically when a molecule of NOx (NO + NO2) is oxidized. It conveys information about the conditions under which O3 is formed and is an important parameter to consider when evaluating impacts from NOx emission sources. We present calculational and observational results on ozone production efficiency based on measurements made from aircraft flights in the Phoenix metropolitan area in May and June of 1998. Constrained steady state box model calculations are used to relate a ratio of O3 production rate to NOx consumption rate (i.e., P(O3)/P(NOz)) to a VOC to NO2 ratio of OH reactivity. Lagrangian calculations show how this ratio generally increases with time due to oxidation chemistry and plume dilution. City to city differences in ozone production efficiency can be attributed to corresponding differences in VOC to NO2 reactivity ratio which in turn reflect emission patterns. Ozone production efficiencies derived from aircraft measurements in 20 plumes show a dependence on NOx concentration similar to that calculated for P(O3)/P(NOz). Calculations are based on data from a single location but are believed to be applicable to a wide range of plumes from different areas.
Eohimalayan fold and thrust belt: Implications for the geodynamic evolution of the NW‐Himalaya (India)
Authors: Wiesmayr Gerhard , Grasemann Bernhard
Published: December 2002

In the Himalayas the Eocene deformation phase is called the Eohimalayan event. By means of a forward and backward balanced cross section along a classical traverse through the Tethyan Himalaya we constrain Eohimalayan SW vergent folding and SW directed thrusting in a belt above a basal thrust at 10 km depth. This thrust is located at the structural position of the Southern Tibetan Detachment System with a NE directed normal sense displacement suggesting Miocene reactivation of a major Eocene contractional fault. Stepwise palinspastic restoration demonstrates that this Eocene contractional fault has been subsequently openly folded due to southwestward propagation of the Himalayan Thrust System.
Restoration of high-level transport activity by human reduced folate carrier/ThTr1 thiamine transporter chimaeras: role of the transmembrane domain 6/7 linker region in reduced folate carrier function
Authors: LIU Xiang Y. , WITT Teah L. , MATHERLY Larry H.
Published: December 2002

The reduced folate carrier (RFC; SLC19A1) is closely related to the thiamine transporter, SLC19A2 (ThTr1). Hydropathy models for these homologous transporters predict up to 12 transmembrane domains (TMDs), with internally oriented N- and C-termini and a large central loop between TMDs 6 and 7. The homologies are localized mostly in the TMDs. However, there is little similarity in their N- and C-terminal domains and the central peptide linkers connecting putative TMDs 1—6 and TMDs 7—12. To explore the functional role of the 61-amino acid central linker in the human RFC (hRFC), we introduced deletions of 49 and 60 amino acids into this region, differing by the presence of a stretch of 11 highly conserved amino acids between the human and rodent RFCs (positions 204—214). An additional hRFC construct was prepared in which only the 11 conserved amino acids were deleted. The resulting hRFCD215—R263Δ, hRFCK204—R263Δ and hRFCK204—R214Δ proteins were transfected into transport-impaired K562 cells. The deletion constructs were all expressed in plasma membranes; however, they were completely inactive for methotrexate and (6S)5-formyl tetrahydrofolate transport. Insertion of non-homologous 73- and 84-amino acid fragments from the structurally analogous ThTr1 linker region into position 204 of hRFCK204—R263Δ restored low levels of transport (16—21% of the wild type). Insertion of the ThTr1 linkers into hRFCD215—R263Δ at position 215 restored 60—80% of wild-type levels of transport. Collectively, our results suggest that the role of the hRFC linker peptide is to provide the proper spatial orientation between the two halves of the hRFC protein for optimal function, and that this is largely independent of amino acid sequence. Our results also demonstrate a critical transport role for the stretch of 11 conserved amino acids starting at position 204 of hRFC.
A prothrombin activator from Bothrops erythromelas (jararaca-da-seca) snake venom: characterization and molecular cloning
Authors: SILVA Márcia B. , SCHATTNER Mirta , RAMOS Celso R.R. , JUNQUEIRA-de-AZEVEDO Inácio L.M. , GUARNIERI Míriam C. , LAZZARI María A. , SAMPAIO Claudio A.M. , POZNER Roberto G. , VENTURA Janaina S. , HO Paulo L. , CHUDZINSKI-TAVASSI Ana M.
Published: December 2002

A novel prothrombin activator enzyme, which we have named ‘berythractivase’, was isolated from Bothrops erythromelas (jararaca-da-seca) snake venom. Berythractivase was purified by a single cation-exchange-chromatography step on a Resource S (Amersham Biosciences) column. The overall purification (31-fold) indicates that berythractivase comprises about 5% of the crude venom. It is a single-chain protein with a molecular mass of 78kDa. SDS/PAGE of prothrombin after activation by berythractivase showed fragment patterns similar to those generated by group A prothrombin activators, which convert prothrombin into meizothrombin, independent of the prothrombinase complex. Chelating agents, such as EDTA and o-phenanthroline, rapidly inhibited the enzymic activity of berythractivase, like a typical metalloproteinase. Human fibrinogen Aα-chain was slowly digested only after longer incubation with berythractivase, and no effect on the β- or γ-chains was observed. Berythractivase was also capable of triggering endothelial proinflammatory and procoagulant cell responses. von Willebrand factor was released, and the surface expression of both intracellular adhesion molecule-1 and E-selectin was up-regulated by berythractivase in cultured human umbilical-vein endothelial cells. The complete berythractivase cDNA was cloned from a B. erythromelas venom-gland cDNA library. The cDNA sequence possesses 2330bp and encodes a preproprotein with significant sequence similarity to many other mature metalloproteinases reported from snake venoms. Berythractivase contains metalloproteinase, desintegrin-like and cysteine-rich domains. However, berythractivase did not elicit any haemorrhagic response. These results show that, although the primary structure of berythractivase is related to that of snake-venom haemorrhagic metalloproteinases and functionally similar to group A prothrombin activators, it is a prothrombin activator devoid of haemorrhagic activity. This is a feature not observed for most of the snake venom metalloproteinases, including the group A prothrombin activators.
Basic fibroblast growth factor as a selective inducer of matrix Gla protein gene expression in proliferative chondrocytes
Authors: STHENEUR Chantal , DUMONTIER Marie-France , GUEDES Claudie , FULCHIGNONI-LATAUD Marie-Claude , TAHIRI Khadija , KARSENTY Gerard , CORVOL Marie Thérèse
Published: December 2002

Matrix Gla protein (MGP) is a member of the vitamin K-dependent γ carboxylase protein family expressed in cartilage. Insulin-like growth factor I (IGF1) stimulates chondrocyte differentiation, whereas basic fibroblast growth factor (FGF2) acts in an opposite manner. We explored the differential expression and regulation by IGF1 and FGF2 of the MGP gene during chondrocyte differentiation. We used a primary culture system of rabbit epiphyseal chondrocytes to show that MGP mRNA is mainly expressed during serum-induced proliferation. Much lower MGP mRNA content is observed in post-mitotic chondrocytes, which newly express α1X procollagen mRNA, a marker of late-differentiated cells. From studies of a series of growth factors, it was shown that IGF1 decreased chondrocyte MGP transcripts, whereas FGF2 had the opposite effect. FGF2 stimulated chondrocyte MGP production in a dose- and time-dependent manner at the mRNA and protein levels. FGF2 acted in a dose- and time-dependent manner, reaching a maximum at 10ng/ml at 20h. The protein synthesis inhibitor cycloheximide did not modify FGF2 action, in agreement with a direct effect. Actinomycin D abolished FGF2-induced stimulation, strongly suggesting that FGF2 modulated MGP gene transcription. We transiently transfected chondrocytes with a construct containing the mouse MGP promoter from −5000 to −168 base pairs, relative to the transcription start site of the gene linked to the luciferase gene (MGP-Luc). In transfected cells, FGF2 stimulated luciferase activity up to sevenfold while IGF1 had no effect. Hence, FGF2 induces transcription of the MGP gene via the 5′-flanking region of the gene. Using a series of deleted MGP-Luc constructs, we identified a sequence of 748 base pairs which was sufficient for transcriptional activation by FGF2. These results led us to postulate that the inhibitory chondrogenic action of FGF2 involves a mechanism whereby MGP gene transcription and protein are induced.
Biochemical and genetic characterization of PpcA, a periplasmic c-type cytochrome in Geobacter sulfurreducens
Authors: LLOYD Jon R. , LEANG Ching , MYERSON Allison L. HODGES , COPPI Maddalena V. , CUIFO Stacey , METHE Barb , SANDLER Steven J. , LOVLEY Derek R.
Published: December 2002

A 9.6kDa periplasmic c-type cytochrome, designated PpcA, was purified from the Fe(III)-reducing bacterium Geobacter sulfurreducens and characterized. The purified protein is basic (pI 9.5), contains three haems and has an N-terminal amino acid sequence closely related to those of the previously described trihaem c7 cytochromes of Geobacter metallireducens and Desulfuromonas acetoxidans. The gene encoding PpcA was identified from the G. sulfurreducens genome using the N-terminal sequence, and encodes a protein of 71 amino acids (molecular mass 9.58kDa) with 49% identity to the c7 cytochrome of D. acetoxidans. In order to determine the physiological role of PpcA, a knockout mutant was prepared with a single-step recombination method. Acetate-dependent Fe(III) reduction was significantly inhibited in both growing cultures and cell suspensions of the mutant. When ppcA was expressed in trans, the full capacity for Fe(III) reduction with acetate was restored. The transfer of electrons from acetate to anthraquinone 2,6-disulphonate (AQDS; a humic acid analogue) and to U(VI) was also compromised in the mutant, but acetate-dependent reduction of fumarate was not altered. The rates of reduction of Fe(III), AQDS, U(VI) and fumarate were also the same in the wild type and ppcA mutant when hydrogen was supplied as the electron donor. When taken together with previous studies on other electron transport proteins in G. sulfurreducens, these results suggest that PpcA serves as an intermediary electron carrier from acetate to terminal Fe(III) reductases in the outer membrane, and is also involved in the transfer of electrons from acetate to U(VI) and humics.