bluuebunny/crossref_metadata_2025 huggingface dataset:
Particulate backscattering ratio at LEO 15 and its use to study particle composition and distribution
Authors: Boss E. , Pegau W. S. , Lee M. , Twardowski M. , Shybanov E. , Korotaev G. , Baratange F.
Published: January 2004

Particulate scattering and backscattering are two quantities that have traditionally been used to quantify in situ particulate concentration. The ratio of the backscattering by particles to total scattering by particles (the particulate backscattering ratio) is weakly dependent on concentration and therefore provides us with information on the characteristics of the particulate material, such as the index of refraction. The index of refraction is an indicator of the bulk particulate composition, as inorganic minerals have high indices of refraction relative to oceanic organic particles such as phytoplankton and detrital material that typically have a high water content. We use measurements collected near the Rutgers University Long‐term Ecosystem Observatory in 15 m of water in the Mid‐Atlantic Bight to examine application of the backscattering ratio. Using four different instruments, the HOBILabs Hydroscat‐6, the WETLabs ac‐9 and EcoVSF, and a prototype VSF meter, three estimates of the ratio of the particulate backscattering ratio were obtained and found to compare well. This is remarkable because these are new instruments with large differences in design and calibration. The backscattering ratio is used to map different types of particles in the nearshore region, suggesting that it may act as a tracer of water movement. We find a significant relationship between the backscattering ratio and the ratio of chlorophyll to beam attenuation. This implies that these more traditional measurements may be used to identify when phytoplankton or inorganic particles dominate. In addition, it provides an independent confirmation of the link between the backscattering ratio and the bulk composition of particles.
Analysis of a temperature inversion event in the lower mesosphere
Authors: Liu Han‐Li , Meriwether John W.
Published: January 2004

Rayleigh lidar measurements of stratospheric and lower mesospheric temperatures obtained at the Urbana Atmospheric Observatory (40.1°N, 88.1°W) on 17/18 November 1997 revealed large temperature inversions at altitudes between 55 to 65 km. Prior to and during a large increase (by up to about 50K) in the amplitude of the mesosphere inversion layer (MIL), a clear and persistent vertical wave structure between 30 and 65 km was observed. The wave has a vertical wavelength of about 12 km and an apparent period of about 12 hours. However, the intrinsic characteristics of the wave are uncertain due to the lack of information regarding the background wind profile and the relative direction of the wave propagation vector with respect to the background wind vector. Two different cases, corresponding to small and large background wind speeds projected onto the horizontal direction of wave propagation, are studied numerically to represent two scenarios with different intrinsic wave characteristics devised to explain the development of the MIL event observed. When the projected background wind is small, the wave is likely to be an inertial‐gravity wave. It is shown that the breaking of such a wave does not produce the large heating rate observed. However, the numerical modeling shows that such an inertial‐gravity wave can modulate the stability of a separate internal gravity wave, and the breaking of this internal gravity wave produces a heating rate similar to the observed rate. When the projected background wind is large, however, the observed wave could be an internal gravity wave with a large intrinsic phase speed. The analysis shows that the breaking of this wave can generate a large heating rate and a MIL that is similar to the observed event. We close with a discussion of the observational implications of these two scenarios. Possible wave sources are also discussed, and it appears that the observed MIL event might be related to a developing frontal system in the tropopause region observed just prior to the onset of the observed event.
An overview of observations of unstable layers during the Turbulent Oxygen Mixing Experiment (TOMEX)
Authors: Hecht J. H. , Liu A. Z. , Bishop R. L. , Clemmons J. H. , Gardner C. S. , Larsen M. F. , Roble R. G. , Swenson G. R. , Walterscheid R. L.
Published: January 2004

The Turbulent Oxygen Mixing Experiment (TOMEX) was designed to measure the atmospheric response to the existence of unstable layers as determined by wind and temperature measurements from 80 to 105 km. TOMEX combined Na lidar measurements, from Starfire Optical Range in Albuquerque, New Mexico, with a launch of a payload from White Sands Missile Range, located between 100 and 150 km south of Starfire. The payload included a trimethyl aluminum chemical release to measure winds and diffusion, a 5‐channel ionization gauge to measure neutral density fluctuations at high vertical resolution, and a 3‐channel photometer experiment to measure atomic oxygen related airglow. The rocket was launched when the lidar data indicated the presence of convectively and dynamically unstable regions between 80 and 100 km altitude. For several hours prior to the launch, there had existed a large amplitude atmospheric gravity wave or tide which brought the background atmosphere into being nearly convectively unstable over the 85 to 95 km region. In addition a large overturning in Na density, possibly due to a convective roll, existed at altitudes around 100 km. This type of instability had not been previously seen and identified in this altitude region. The TOMEX payload measured the existence of Kelvin‐Helmholz billows, enhanced neutral density fluctuations, enhanced energy dissipation, and well‐mixed regions. These features were associated with convectively unstable regions, dynamically unstable regions, convective rolls, and the presence of this large wave. The unstable regions were persistent and covered large vertical (and horizontal regions) of the atmosphere. The atmospheric mixing and energy dissipation appeared to be largely determined by the presence and nature of these instabilities.
Time Empirical Ionospheric Correction Model (STORM) response in IRI2000 and challenges for empirical modeling in the future
Authors: Araujo‐Pradere E. A. , Fuller‐Rowell T. J. , Bilitza D.
Published: January 2004

IRI2000 [Bilitza, 2001] now contains a geomagnetic activity dependence based on the Time Empirical Ionospheric Correction Model (STORM) [Araujo‐Pradere and Fuller‐Rowell, 2002; Araujo‐Pradere et al., 2002]. The storm correction is driven by the previous time history of ap and is designed to scale the quiet time F layer critical frequency (foF2) to account for storm‐time changes in the ionosphere. The quality of the storm‐time correction was recently evaluated by comparing the model with the observed ionospheric response during all the significant geomagnetic storms in 2000 and 2001. The model output was compared with the actual ionospheric response at 15 stations for each storm. These quantitative comparisons using statistical metrics showed that the model captures the decreases in electron density particularly well in summer and equinox conditions, but is not so good during winter conditions. To further assess the capabilities of the model, STORM has been compared in detail with observations during the Bastille Day storm in July 2000. This storm, considered to be on the extreme end of the statistical scale of storm magnitude, highlights two main areas were challenges remain for the empirical storm‐time ionospheric model. The first is the rapid onset of the positive storm phase; the second is the regional composition changes that can affect one longitude sector at the expense of another for a particular storm. Both these challenges, although appreciated during the development of STORM, remain to be addressed.
GPS proxy model for real‐time UHF satellite communications scintillation maps from the Scintillation Network Decision Aid (SCINDA)
Authors: Caton R. G. , McNeil W. J. , Groves K. M. , Basu S.
Published: January 2004

In order to provide a more reliable situational awareness of scintillation impacts on users of space‐based communication/navigation systems, L‐band scintillation measurements from GPS satellites are ingested, in real time, to the Scintillation Network Decision Aid (SCINDA) model. SCINDA is a real‐time, data‐driven communication outage forecast and alert system developed by the Air Force Research Laboratory at Hanscom Air Force Base and made operational through a joint effort between the U.S. Air Force and the U.S. Navy. UHF and L‐band scintillation parameters are measured, modeled, and propagated in time to provide a regional specification of the scintillation environment in an effort to mitigate the impacts on the satellite communications (SATCOM) community. In an effort to provide UHF SATCOM users with a more consistent estimation of scintillation impacts on their systems, GPS sensors, measuring S4 at L‐band frequency, are now used as a supplement to the stationary UHF links dramatically increasing the regional coverage at each individual station, particularly those located outside the anomaly crest. Three‐dimensional representations of GPS observed plumes are mapped to the ground from the location of a selected satellite, producing a “scintillation specification map detailing “outage” regions on the globe. In this paper we present results from a validation study of the GPS proxy model and demonstrate its usefulness as an adjunct to the SCINDA model in producing the most accurate and reliable nowcast and forecast scintillation specification products available to UHF SATCOM users.
Topside Ionogram Scaler With True Height Algorithm (TOPIST): Automated processing of ISIS topside ionograms
Authors: Bilitza Dieter , Huang Xueqin , Reinisch Bodo W. , Benson Robert F. , Hills H. Kent , Schar William B.
Published: January 2004

The United States/Canadian ISIS‐1 and ISIS‐2 satellites collected several million topside ionograms in the 1960s and 1970s with a multinational network of ground stations that provided good global coverage. However, processing of these ionograms into electron density profiles required time‐consuming manual scaling of the traces from the analog ionograms, and as a result, only a few percent of the ionograms had been processed into electron density profiles. In recent years an effort began to digitize the analog recordings to prepare the ionograms for computerized analysis. As of November 2002, approximately 390,000 ISIS‐1 and ISIS‐2 digital topside‐sounder ionograms have been produced. The Topside Ionogram Scaler With True Height Algorithm (TOPIST) program was developed for the automated scaling of the echo traces and for the inversion of these traces into topside electron density profiles. The program is based on the techniques that have been successfully applied in the analysis of ground‐based Digisonde ionograms. The TOPIST software also includes an “editing option” for manual scaling of the more difficult ionograms, which could not be scaled during the automated TOPIST run. TOPIST is now successfully scaling ∼60% of the ISIS ionograms, and the electron density profiles are available through the online archive of the National Space Science Data Center at ftp://nssdcftp.gsfc.nasa.gov/spacecraft_data/isis/topside_sounder. This data restoration effort is producing a unique global database of topside electron densities over more than one solar cycle, which will be of particular importance for improvements of topside ionosphere models, especially the International Reference Ionosphere.
Physiological and biochemical controls over methyl halide emissions from rice plants
Authors: Redeker K. R. , Manley S. L. , Walser M. , Cicerone R. J.
Published: January 2004

This paper investigates physiological and biochemical aspects of methyl halide production in rice plants over two growing seasons. Multiple separate mechanisms appear to be responsible for production of methyl halides in rice plant tissues. Evidence for multiple mechanisms is found in timing of peak emissions of methyl halides from rice, inconsistent effects of competitive inhibitors on methyl halide emissions, and large differences in methyl halide emission rates when compared to plant tissue halide concentrations. Other results show that chloride, bromide, and iodide ion concentrations in plant tissue appear to be regulated throughout the season, and observed changes in leaf tissue concentration cannot explain observed methyl halide emissions. The Km for methyl iodide formation in leaf tissue cell‐free extract is 0.018 mM, suggesting a very efficient mechanism. Of the seven competitive inhibitors used, only thiol had a consistently strong effect on both methyl iodide and methyl bromide.
A model of the Earth's Dole effect
Authors: Hoffmann Georg , Cuntz Matthias , Weber Christine , Ciais Philippe , Friedlingstein Pierre , Heimann Martin , Jouzel Jean , Kaduk Jörg , Maier‐Reimer Ernst , Seibt Ulrike , Six Katharina
Published: January 2004

The Earth's Dole effect describes the isotopic 18O/16O‐enrichment of atmospheric oxygen with respect to ocean water, amounting under today's conditions to 23.5‰. We have developed a model of the Earth's Dole effect by combining the results of three‐dimensional models of the oceanic and terrestrial carbon and oxygen cycles with results of atmospheric general circulation models (AGCMs) with built‐in water isotope diagnostics. We obtain a range from 22.4‰ to 23.3‰ for the isotopic enrichment of atmospheric oxygen. We estimate a stronger contribution to the global Dole effect by the terrestrial relative to the marine biosphere in contrast to previous studies. This is primarily caused by a modeled high leaf water enrichment of 5–6‰. Leaf water enrichment rises by ∼1‰ to 6–7‰ when we use it to fit the observed 23.5‰ of the global Dole effect. The present model is designed to be utilized in forthcoming paleo studies allowing a quantitative analysis of long‐term observations from polar ice cores.
Paleomagnetism and 40Ar/39Ar Chronology of Lavas from Meseta del Lago Buenos Aires, Patagonia
Authors: Brown Laurie L. , Singer Brad S. , Gorring Matthew L.
Published: January 2004

As part of a larger project investigating paleosecular variation in South America, 36 paleomagnetic and geochronology sites were sampled on Meseta del Lago Buenos Aires (47°S, 289°E), 200 km east of the active plate boundary in southern Patagonia. Basaltic lavas sampled range from late Miocene to late Pleistocene yet most of the individual lavas are younger than 3.3 Ma. Thirty‐eight isochron ages determined via 40Ar/39Ar incremental‐heating experiments frame a detailed stratigraphy. The isochron ages range from 66.9 ± 4.1 ka for scoria cones and a youthful lava flow in the Rio Pinturas valley to 10.12 ± 1.35 Ma for thick plateau‐forming lavas exposed along the SE edge of the Meseta. The last 3.3 myr is characterized by seven episodes of volcanism at ca. 3.2–3.0 Ma, 2.4 Ma, 1.7 Ma, 1.35 Ma, 1.0 Ma, 750 ka, 430–330 ka, and <110 ka. The bulk of lavas forming the surface of the Meseta erupted in the last 1.7 my. All sites have stable magnetization, and after step demagnetization using either thermal or alternating field techniques, yield characteristic directions held by magnetite and/or titanomagnetite. Ten sites have distinct transitional directions (defined by pole latitudes <55°), and associated ages indicate possible connections to known reversals within the Matuyama Chron, including the onset of the Jaramillo subchron (1.016 ± 0.01 Ma), the Cobb Mountain subchron (1.25 ± 0.03 Ma), the Ontong‐Java 1 event (1.37 ± 0.03 Ma), and the termination of the Olduvai subchron (1.72 ± 0.02 Ma). Remaining sites are divided into normal (14 sites) and reversed polarity (12 sites). At 95% confidence mean normal and reversed directions overlap. The mean direction for 26 sites is I = −63.0°, D = 3.4°, α95 = 5.4°, which is indistinguishable from the expected geocentric axial dipole. Paleosecular variation, measured by the dispersion of virtual geomagnetic poles about the rotation axis, is higher than expected at 20.0°. Model G, using data for the past 5 Myr, predicts a dispersion of 17°. This discrepancy may be due to true dispersion of the field in southern South America or it may be an artifact of inadequate sampling.
Simulated Sea Surface Salinity variability in the tropical Pacific
Authors: Wang Xiaochun , Chao Yi
Published: January 2004

Sea Surface Salinity (SSS) variability from a hindcast run of an oceanic general circulation model (OGCM) forced by daily NCEP‐NCAR reanalysis from 1990 to 2001 is analyzed. The purpose is to test the capability of the model in terms of the salinity simulation and provide insights for the future SSS observation from space. With daily forcing, the model can reproduce SSS change of the tropical Pacific on different time scales by comparing with the Tropical Atmosphere Ocean (TAO) mooring observation. Our model results show that the western tropical Pacific is a large variability center on different time scales. On the interannual time scale, the standard deviation of SSS in the region could reach 0.5 practical salinity unit (psu). However, the eastern tropical Pacific shows relatively weak SSS variability (0.1 psu). On the intraannual time scale (60–360 days), the SSS variability in the western tropical Pacific is around 0.2 psu. The model SSS variability for the intraseasonal time scale (30–60 days) has a magnitude around 0.1 psu and tends to elongate along the latitudes of large meridional SSS gradient. On time scale shorter than 30 days, the model SSS variability center is near the equator and has a magnitude less than 0.1 psu. Relevance to the upcoming salinity satellite mission is discussed.
Effective ice particle densities for cold anvil cirrus
Authors: Heymsfield Andrew J. , Schmitt Carl G. , Bansemer Aaron , Baumgardner Darrel , Weinstock Elliot M. , Smith Jessica T. , Sayres David
Published: January 2004

This study derives effective ice particle densities (ρe) from data collected by the NASA WB‐57F aircraft near the tops of Florida anvils during the Cirrus Regional Study of Tropical Anvils and Cirrus Layers (CRYSTAL) Florida Area Cirrus Experiment (FACE). The ρe‐ice particle mass divided by the volume of an equivalent diameter liquid sphere‐, is obtained for particle populations () and single sizes from a few to 200–300 μm in maximum dimension using measurements of condensed water content and particle size distributions. Density values are needed for numerical modeling of ice cloud microphysical properties and remote sensing retrievals, and have not up to now been characterized for cold ice clouds containing mixed particle habits. The decrease with increasing slopes of gamma size distributions fitted to the size distributions, ranging from 0.15–0.91 g cm−3. For single sizes, ρe obeys a power‐law with an exponent of about −0.4.
The 2003 heat wave in Europe: A shape of things to come? An analysis based on Swiss climatological data and model simulations
Authors: Beniston Martin
Published: January 2004

The 2003 heat wave that affected much of Europe from June to September bears a close resemblance to what many regional climate models are projecting for summers in the latter part of the 21st century. Model results suggest that under enhanced atmospheric greenhouse‐gas concentrations, summer temperatures are likely to increase by over 4°C on average, with a corresponding increase in the frequency of severe heat waves. Statistical features of the 2003 heat wave for the Swiss site of Basel are investigated and compared to both past, 20th century events and possible future extreme temperatures based on model simulations of climatic change. For many purposes, the 2003 event can be used as an analog of future summers in coming decades in climate impacts and policy studies.
The nonlinear Northern Hemisphere winter atmospheric response to ENSO
Authors: Wu Aiming , Hsieh William W.
Published: January 2004

A nonlinear projection of the tropical Pacific sea surface temperature anomalies (SSTA) onto the Northern Hemisphere winter 500‐mbar geopotential height (Z500) by a neural network reveals asymmetric atmospheric patterns associated with El Niño and La Niña. While the linear response of Z500 to tropical Pacific SSTA is largely confined over North Pacific and North America, the nonlinear response, mainly a quadratic response to the SSTA, reveals that regardless of the sign of the SSTA, positive Z500 anomalies are found over the central‐eastern North America, North Atlantic and western Europe, and negative Z500 anomalies over the west coast of North America, Scandinavia and eastern Europe—consistent with the positive Pacific‐North America (PNA) teleconnection pattern and the positive North Atlantic Oscillation (NAO) pattern being excited.
Seismological constraints on the structure and composition of western Deccan Volcanic Province from converted phases
Authors: Mohan G. , Ravi Kumar M.
Published: January 2004

Receiver function analysis using teleseismic data from one broadband and nine short period stations, was carried out in a 50 km x 100 km area, near Mumbai (Bombay), encompassing the coastal plains of the rifted margin of the western Deccan Volcanic Province (DVP) of India. This region is characterized by a thick (36–41 km) shield like crust which is at variance with earlier inferences in this part of DVP. The crustal composition as inferred from the Poisson's ratio of 0.26 ± 0.01 is felsic to intermediate in nature. The continental crust exhibits structural controls similar to the offshore shelf region but does not exhibit any typical seismic signatures of magmatic underplating nor appears to be perturbed by the Deccan volcanism.
Mineral magnetic properties of loess/paleosol couplets of the central loess plateau of China over the last 1.2 Myr
Authors: Deng Chenglong , Zhu Rixiang , Verosub Kenneth L. , Singer Michael J. , Vidic Natasa J.
Published: January 2004

We have conducted a multiparameter investigation of 15 loess‐paleosol couplets (S0/L1 to S14/L15) from the Jiaodao section in the central loess plateau of China using environmental magnetic approaches coupled with soil science techniques. The magnetic parameters display systematic variations that seem to be closely related to paleoclimate variations and intensity of pedogenesis. High‐temperature susceptibility curves of paleosols show a generally decreasing trend in reversibility from the base of the Lishi Formation to the Holocene black loam, possibly indicating a decrease in weathering intensity. This may reflect a long‐term increase in aridity and/or a general long‐term cooling trend of the interior of the Asian continent from 1.2 Ma to the present. Several samples display wasp‐waisted hysteresis loops. These are most pronounced in moderately enhanced paleosols, less pronounced in the practically unaltered loess, and subdued in the well‐developed paleosols, but wasp waistedness reappears in the most developed paleosols. This wasp‐waistedness sequence suggests that the composition, concentration, and grain size of magnetic minerals all contribute to the hysteresis behavior of samples from the studied loess‐paleosol sequence, but each factor has a different effect at different stages of pedogenesis.
Variability in river runoff distribution in the Eurasian Basin of the Arctic Ocean
Authors: Anderson Leif G. , Jutterström Sara , Kaltin Staffan , Jones E. Peter , Björk Göran
Published: January 2004

The distribution of freshwater within the Arctic Ocean and its export from it are intimately involved in climate and climate change processes both within and outside the Arctic Ocean. River runoff in the Arctic Ocean constitutes a major part of the Arctic Ocean freshwater budget. Within the Arctic Ocean, variability in the distribution of river runoff will be reflected in the location of the cold halocline that isolates the sea ice from the warm Atlantic Layer. Outside the Arctic Ocean, such variability will impact on the salinity of North Atlantic waters (Great Salinity Anomaly) and on deep convection areas of the North Atlantic Ocean, and thereby potentially on global thermohaline circulation. Rivers entering the Arctic Ocean have high levels of total alkalinity that contribute significantly to the total alkalinity of the surface Polar Mixed Layer. We exploit total alkalinity data to trace river runoff in the surface Polar Mixed Layer and to observe variability in the river runoff distribution in the Eurasian Basin over the period 1987–2001. The river runoff front changed from a position over the Gakkel Ridge in 1987 and 1991 to over the Lomonosov Ridge in 1996, and returned to a midpoint between the two ridges in 2001. Wind field changes as characterized by the Arctic Oscillation index are considered to be a major factor in determining ice and surface water flow. We note a correlation with 4–6 years delay between changes in river runoff distribution and the Arctic Oscillation index. We show that the delay can be inferred from a geostrophic flow calculation.
Model studies of near‐inertial motion on the continental shelf off northeast Spain: A three‐dimensional/two‐dimensional/one‐dimensional model comparison study
Authors: Xing Jiuxing , Davies Alan M. , Fraunie Philippe
Published: January 2004

A three‐dimensional nonlinear model of the Balearic Sea region is used to examine the spatial distribution of wind‐induced near‐inertial internal waves. Results from the model are compared with those from two‐dimensional cross‐section and single‐point models. In the case of motion induced by a wind pulse, there is no significant along‐shelf flow, and comparable solutions are obtained from the three‐and two‐dimensional models. However, when forced with a realistic wind, a significant along‐shelf flow is produced that is larger in the cross‐section model than in the three‐dimensional model because of the absence of an along‐shelf pressure gradient. Associated with this change in flow are important differences in across‐shelf currents and temperature fields that influence the distribution of near‐inertial motion. Since the point model cannot take account of internal pressure gradients, near‐inertial internal waves are absent. However, when some account of barotropic pressure gradients related to local wind stress are included, currents and inertial oscillations were in better agreement with the three‐dimensional model than with the cross‐section model. Although the major features of the wind‐induced deepening of the thermocline could be reproduced by the single‐point model, the absence of internal waves and mixing associated with them lead to a sharper thermocline than in the three‐dimensional model. Comparison of two‐ and one‐dimensional models with the full three‐dimensional model shows some severe limitations in the simpler models.
Cloud‐to‐ground lightning activity in hail‐bearing storms
Authors: Soula Serge , Seity Yann , Feral Laurent , Sauvageot Henri
Published: January 2004

The cloud‐to‐ground lightning flash (CG) produced by several apparent hailstorms are analyzed in different locations of southern Europe. The hail detection is performed via four different analysis techniques: radar reflectivity factor estimation, radar echo shape analysis, polarimetric hydrometeor identification, and reflectivity difference between radars with different wavelengths. The CG parameters considered are the flash rate and density, the flash polarity, the multiplicity, and the peak current. Some of the observed storms exhibit hail‐bearing cell features, while others exhibit heavy precipitation rates without any apparent hail production. One of the hailstorms can be classified as severe because reported hailstorm diameters reach 39 mm. The CG lightning characteristics of both types of storms are compared. The CG rates corresponding to all hail‐bearing storms are singularly lower than those of rain‐only storms, typically by a factor 5. So, the CG rate of the hail‐bearing storms considered does not exceed 2 min−1 while it can reach about 12 min−1 for heavy rain‐bearing storms. Moreover, some of them can produce especially high positive CG proportions associated with negative CGs with low values of peak current and multiplicity. This last observation suggests that the negative charge available for CG flashes is weak within the cloud when positive CG flashes are dominant. In order to interpret the low CG rates observed in the case of hail‐bearing storms several interpretations are discussed, but it would be necessary to know the intracloud flash activity in such cases of storms in order to enrich the discussion.
Evolution of lightning and the possible initiation/triggering of lightning discharges by the lower positive charge center in an isolated thundercloud in the tropics
Authors: Pawar S. D. , Kamra A. K.
Published: January 2004

The evolution of lightning and the shape of recovery curves after multiple‐discharge flashes in a thundercloud have been studied from the surface measurements of electric field and Maxwell current near a tropical thundercloud. Observations suggest a tripole structure of the cloud and that its lower positive charge center (LPCC) plays a dominant role in initiating/triggering an intracloud (IC) or cloud‐to‐ground (CG) lightning discharge. IC discharges in the initial stage of thundercloud are followed by CG discharges from the LPCC and then by two distinct groups of multiple‐discharge flashes. Each flash in the first group consists of an IC discharge triggered by a CG discharge and in the second group a CG discharge triggered by an IC discharge. Flashes in each group are bunched together for ∼15–20 min and occur with almost a regular periodicity of 1–1.5 min. The Maxwell current during every such flash in both groups has a bipolar transient and a positive overshoot that subsequently relaxes back to its predischarge value. The magnitudes of overshoot for the flashes in the first group are found to be much lower than those for the flashes in the second group. From a small portion of the recovery curves of such multiple‐discharge flashes, one can conclude that the rate of charge buildup in the main negative charge center is higher than that in the LPCC.
Observed variations of tropical convective available potential energy
Authors: DeMott Charlotte A. , Randall David A.
Published: January 2004

Data from selected tropical radiosonde stations (located between 25°S and 25°N) are used to compute multidecadal trends in convective available potential energy (CAPE). Positive trends slightly outnumber negative trends, with the greatest concentration of positive trends occurring in the western Pacific Ocean and the Caribbean Sea. Analysis shows that positive and negative CAPE trends are primarily driven by same‐signed trends in low‐level moisture, while lapse rate trends play a secondary role and may either increase or decrease the magnitude of the CAPE trends. Monthly CAPE anomalies are generally positively correlated with sounding‐derived precipitable water (PW) and lapse rate as well as with Special Sensor Microwave Imager (SSMI)‐derived PW for retrievals located over the sounding location. Sounding‐derived PW estimates for island and coastal locations were averaged and compared to tropical SSMI PW estimates, which are available only over the oceans. The two time series are poorly correlated, suggesting that the limited number of sounding stations considered herein does not adequately capture tropical‐wide variability. The relationship of CAPE changes to PW and lapse rate changes is examined on a variety of timescales for evidence of quasi‐equilibrium (QE) behavior, in which convection acts to maintain an approximately moist adiabatic temperature profile. Strict QE, in which convection maintains an exactly moist adiabatic temperature profile, is assumed in the convective parameterizations of many general circulation models. PW and lapse rate anomalies are negatively correlated on multidecadal timescales and on monthly timescales in heavily raining regions, in support of QE theory. However, no such negative correlation is seen over the course of the seasonal cycle or for monthly timescales in low‐rain areas. CAPE anomalies were compared to nearest‐grid‐point monthly precipitation anomalies derived from surface‐based rain gauges. Correlations are small and centered at about zero. Mean tropical rainfall estimates, based on a combination of satellite and surface gauge data, are uncorrelated with the mean tropical SSMI PW estimates.
Diffusion as the main process for mass transport in very low water content argillites: 2. Fluid flow and mass transport modeling
Authors: Patriarche Delphine , Ledoux Emmanuel , Michelot Jean‐Luc , Simon‐Coinçon Régine , Savoye Sébastien
Published: January 2004

On the basis of chloride concentrations of pore water in the Tournemire massif (part 1), a conceptual model for mass transport in argillites by diffusion is proposed. From this conceptual model and current knowledge of the geological history of the massif, one‐dimensional numerical simulations are formulated for chloride transport in Tournemire massif over the past 53 Ma. Good agreement between experimental data and calculated values for both diffusion coefficients and concentrations of chloride confirms that diffusion is the main process for mass transport in the massif. This model is also tested using deuterium contents of pore water, applying variable concentrations to meteoric water (circulating in system boundary layers) based on the thermal dependency of its isotopic composition. These simulations reveal the likely important role of lithologic heterogeneities, such as fractures, in the horizontal distribution of tracer concentrations.
Conditional gene knock‐down by CRE‐dependent short interfering RNAs
Authors: Fritsch Lauriane , Martinez Luis A , Sekhri Redha , Naguibneva Irina , Gérard Mathieu , Vandromme Marie , Schaeffer Laurent , Harel‐Bellan Annick
Published: January 2004

Short interfering RNAs (siRNAs) are short (21–23 nt) double‐stranded RNAs that direct the sequence‐specific degradation of corresponding mRNAs, resulting in suppression of gene activity. siRNAs are powerful tools for gene functional analysis in mammals. Chemically synthesized siRNAs permit transient gene repression but preclude inhibition of stable gene products as well as long‐term phenotypic analyses. Permanent gene suppression can be achieved by transcribing siRNAs as stem–loop precursors from Pol III promoters. This approach, however, has a major limitation: inhibition cannot be controlled in a time‐ or tissue‐specific manner. Thus, the approach cannot be applied to genes essential for cell survival or cell proliferation. To overcome these limitations, we have designed a CRE–lox‐based strategy that allows one to repress gene activity in a time‐dependent manner in cells, and in a time‐ or tissue‐dependent manner in animals. Our approach promises to improve dramatically the procedures for functional genetics in mammals.
In vivo analysis of the overlapping functions of DnaK and trigger factor
Authors: Genevaux Pierre , Keppel France , Schwager Françoise , Langendijk‐Genevaux Petra S , Hartl F Ulrich , Georgopoulos Costa
Published: January 2004

Trigger factor (TF) is a ribosome‐bound protein that combines catalysis of peptidyl‐prolyl isomerization and chaperone‐like activities in Escherichia coli. TF was shown to cooperate with the DnaK (Hsp70) chaperone machinery in the folding of newly synthesized proteins, and the double deletion of the corresponding genes (tig and dnaK) exhibited synthetic lethality. We used a detailed genetic approach to characterize various aspects of this functional cooperation in vivo. Surprisingly, we showed that under specific growth conditions, one can delete both dnaK and tig, indicating that bacterial survival can be maintained in the absence of these two major cytosolic chaperones. The strain lacking both DnaK and TF exhibits a very narrow temperature range of growth and a high level of aggregated proteins when compared to either of the single mutants. We found that, in the absence of DnaK, both the N‐terminal ribosome‐binding domain and the C‐terminal domain of unknown function are essential for TF chaperone activity. In contrast, the central PPIase domain is dispensable. Taken together, our data indicate that under certain conditions, folding of newly synthesized proteins in E. coli is not totally dependent on an interaction with either TF and/or DnaK, and suggest that additional chaperones may be involved in this essential process.
Apoptosis does not play an important role in the resistance of ‘immune’Penaeus japonicus against white spot syndrome virus
Authors: Wu J L , Muroga K
Published: January 2004

We previously demonstrated that kuruma shrimp, Penaeus japonicus, exposed to white spot syndrome virus (WSSV) became resistant (‘immune’ shrimp) to subsequent challenge with the virus. The present study investigated the role of apoptosis in the ‘immune’ shrimp during a secondary challenge with WSSV. When naive kuruma shrimp were intramuscularly injected with WSSV at a high or low dose, apoptosis was often detected by TUNEL assay in the lymphoid organ (LO), mainly in the early stage of the infection. A significantly higher incidence of apoptosis was observed in the LO of the shrimp injected with the high dose of WSSV (cumulative mortality: 100%) than in the shrimp injected with the low dose (cumulative mortality: 0%). When ‘immune’ and naive shrimp were injected with an equal dose of WSSV, the incidence of apoptosis was significantly lower in the ‘immune’ shrimp than in the naive shrimp. This difference is assumed to result from a substantial reduction of the virus by humoral neutralizing factor in the ‘immune’ shrimp. These results suggest that apoptosis is not a principal protective factor in ‘immune’ shrimp.
Localization of carbohydrate terminals on Tetracapsuloides bryosalmonae using lectin histochemistry and immunogold electron microscopy
Authors: Morris D J , Adams A
Published: January 2004

Tetracapsuloides bryosalmonae is the myxozoan parasite that causes the commercially important proliferative kidney disease (PKD) in salmonid aquaculture. Previous studies on the binding of lectins to T. bryosalmonae identified Griffonia simplificola agglutinin I (GS I) as useful for parasite identification. This lectin was also implicated as recognizing antigenic structures on the parasite. Here, we examine the histochemical staining and ultrastructural localization of a panel of 21 lectins on the extrasporogonic stage of T. bryosalmonae. The histochemical staining studies indicated that the majority of lectins bound to the renal stages of T. bryosalmonae, however not all of these lectins could be successfully localized using immunogold electron microscopy. Of the lectins that were localized many, including GS I, bound to membranes associated with the lysosomal pathway within the extrasporogonic primary cell of the parasite, indicating that these organelles are rich in glycoconjugates. The histochemical staining of Erythrina cristagalli ECL was unique and highlighted a different distribution of glycoconjugates in the periphery of some extrasporogonic parasites within the renal sinuses when compared with stages in the interstitium, suggesting the presence of distinct blood forms of T. bryosalmonae.
The effect of in vivo growth on the cellular and extracellular components of the marine bacterial pathogen Photobacterium damsela subsp. piscicida
Authors: Bakopoulos V , Hanif A , Poulos K , Galeotti M , Adams A , Dimitriadis G J
Published: January 2004

Photobacterium damsela subsp. piscicida, the causative agent of fish pasteurellosis, was grown in vivo. Bacterial cells and extracellular products (ECPs) were analysed via electrophoresis and immunoblot analysis, using specific sea bass antisera. Growth in vivo induced the synthesis of unique bacterial cell proteins at >206, 206, 21.3, 18, 7.6 and <7.6 kDa. Sea bass serum raised against live bacterial cells of the pathogen and especially a sea bass serum raised against formalin‐inactivated bacterial cells grown in a specific novel medium recognized the novel antigens at >206 (associated with iron sequestration), 21.3, 7.6 and <7.6 kDa, suggesting that the latter medium conserves the synthesis of natural bacterial cell proteins in vitro. In vivo growth of the pathogen induced the synthesis of more toxic ECPs in comparison with in vitro growth and an inverse correlation between total protein concentration in the ECPs and toxicity per unit of protein was observed. Substrate‐polyacrylamide electrophoresis revealed the presence of in vivo synthesized ECPs of the pathogen (proteases) at 175, 132, <79 and 48.3 kDa. Histological examination of tissues isolated from fish injected with these ECPs revealed inflammatory and necrotic lesions in the spleen, liver, head kidney, intestine and heart as soon as 48 h post‐introduction of the ECPs.
Atlantic salmon, Salmo salar L., previously infected with Neoparamoeba sp. are not resistant to re‐infection and have suppressed phagocyte function
Authors: Gross K A , Morrison R N , Butler R , Nowak B F
Published: January 2004

Previous studies have indicated that Atlantic salmon, Salmo salar L., affected by amoebic gill disease (AGD) are resistant to re‐infection. These observations were based upon a comparison of gross gill lesion abundance between previously infected and naïve control fish. Anecdotal evidence from Atlantic salmon farms in southern Tasmania suggests that previous infection does not protect against AGD as indicated by a lack of temporal change in freshwater bathing intervals. Experiments were conducted to determine if previous infection of Atlantic salmon with Neoparamoeba sp. would provide protection against challenge and elucidate the immunological basis of any protection. Atlantic salmon were infected with Neoparamoeba sp. for 12 days then treated with a 4‐h freshwater bath. Fish were separated into two groups and maintained in either sea water or fresh water for 6 weeks. Fish were then transferred to one tank with a naïve control group and challenged with Neoparamoeba sp. Fish kept in sea water had lower mortality rates compared with first time exposed and freshwater maintained fish, however, these data are believed to be biased by ongoing mortalities during the seawater maintenance phase. Phagocyte function decreased over exposure time and freshwater maintained fish demonstrated an increased ability to mount a specific immune response. These results suggest that under the challenge conditions herein described, antigen exposure via infection does not induce protection to subsequent AGD.
Map‐based cloning of a fertility restorer gene, Rf‐1, in rice (Oryza sativa L.)
Authors: Komori Toshiyuki , Ohta Shozo , Murai Nobuhiko , Takakura Yoshimitsu , Kuraya Yoshiki , Suzuki Shoichi , Hiei Yukoh , Imaseki Hidemasa , Nitta Naoto
Published: January 2004

A rice nuclear gene, Rf‐1, restores the pollen fertility disturbed by the BT‐type male sterile cytoplasm, and is widely used for commercial seed production of japonica hybrid varieties. Genomic fragments carrying Rf‐1 were identified by conducting chromosome walking and a series of complementation tests. Isolation and analysis of cDNA clones corresponding to the fragments demonstrated that Rf‐1 encodes a mitochondrially targeted protein containing 16 repeats of the 35‐aa pentatricopeptide repeat (PPR) motif. Sequence analysis revealed that the recessive allele, rf‐1, lacks one nucleotide in the putative coding region, presumably resulting in encoding a truncated protein because of a frame shift. Rice Rf‐1 is the first restorer gene isolated from cereal crops that has the property of reducing the expression of the cytoplasmic male sterility (CMS)‐associated mitochondrial gene like many other restorer genes. The present findings may facilitate not only elucidating the mechanisms of male sterility by the BT cytoplasm and its restoration by Rf‐1 but also isolating other restorer genes from cereal crops, especially rice.
Gain‐of‐function and loss‐of‐function phenotypes of the protein phosphatase 2C HAB1 reveal its role as a negative regulator of abscisic acid signalling
Authors: Saez Angela , Apostolova Nadezda , Gonzalez‐Guzman Miguel , Gonzalez‐Garcia Mary Paz , Nicolas Carlos , Lorenzo Oscar , Rodriguez Pedro L.
Published: January 2004

HAB1 was originally cloned on the basis of sequence homology to ABI1 and ABI2, and indeed, a multiple sequence alignment of 32 Arabidopsis protein phosphatases type‐2C (PP2Cs) reveals a cluster composed by the four closely related proteins, ABI1, ABI2, HAB1 and At1g17550 (here named HAB2). Characterisation of transgenic plants harbouring a transcriptional fusion ProHAB1: green fluorescent protein (GFP) indicates that HAB1 is broadly expressed within the plant, including key target sites of abscisic acid (ABA) action as guard cells or seeds. The expression of the HAB1 mRNA in vegetative tissues is strongly upregulated in response to exogenous ABA. In this work, we show that constitutive expression of HAB1 in Arabidopsis under a cauliflower mosaic virus (CaMV) 35S promoter led to reduced ABA sensitivity both in seeds and vegetative tissues, compared to wild‐type plants. Thus, in the field of ABA signalling, this work represents an example of a stable phenotype in planta after sustained overexpression of a PP2C genes. Additionally, a recessive T‐DNA insertion mutant of HAB1 was analysed in this work, whereas previous studies of recessive alleles of PP2C genes were carried out with intragenic revertants of the abi1‐1 and abi2‐1 mutants that carry missense mutations in conserved regions of the PP2C domain. In the presence of exogenous ABA, hab1‐1 mutant shows ABA‐hypersensitive inhibition of seed germination; however, its transpiration rate was similar to that of wild‐type plants. The ABA‐hypersensitive phenotype of hab1‐1 seeds together with the reduced ABA sensitivity of 35S:HAB1 plants are consistent with a role of HAB1 as a negative regulator of ABA signalling. Finally, these results provide new genetic evidence on the function of a PP2C in ABA signalling.
Identification of a mitochondrial external NADPH dehydrogenase by overexpression in transgenic Nicotiana sylvestris
Authors: Michalecka Agnieszka M. , Agius Stephanie C. , Møller Ian M. , Rasmusson Allan G.
Published: January 2004

The plant respiratory chain contains a complex setup of non‐energy conserving NAD(P)H dehydrogenases, the physiological consequences of which are highly unclear. An expression construct for the potato (Solanum tuberosum L., cv. Desiree) ndb1 gene, a homologue of bacterial and fungal type II NAD(P)H dehydrogenases, was introduced into Nicotiana sylvestris. Transgenic lines with high transcript and protein levels for St‐NDB1 had up to threefold increased activity of external NADPH dehydrogenase in isolated mitochondria as compared to the wild type (WT). In two lines, the external NADPH dehydrogenase activity was instead 10‐fold decreased, indicating that the corresponding N. sylvestris gene had been suppressed. Activities of external and internal rotenone‐insensitive NADH dehydrogenases were unchanged in the transgenic lines. The results demonstrate that the St‐ndb1 encodes an external dehydrogenase specific for NADPH and dependent on calcium for activity. Transgenic lines overexpressing St‐ndb1 had specifically increased protein levels for alternative oxidase and uncoupling protein, as compared to the WT and one co‐suppressing line. This indicates cross‐talk in the expressional control, or metabolic conditions influencing it, for the different categories of energy‐dissipating proteins that bypass oxidative phosphorylation. The potential effects of external NADPH oxidation on other cellular processes are discussed.