bluuebunny/crossref_metadata_2025 huggingface dataset:
Poliovirus vaccination: current understanding of poliovirus interactions in humans and implications for the eradication of poliomyelitis
Authors: Minor Philip D.
Published: October 2003

Poliomyelitis is a paralytic disease of the motor neurones of the central nervous system, which is caused by poliovirus. The virus is transmitted by the faecal–oral route, and if virus replication is confined to the gut, it is harmless. Poliomyelitis is an ancient human disease, but was rare until the beginning of the 20th century, when children began to be exposed to the virus at older ages and were, therefore, no longer protected by maternal antibody, which had already been lost. Inactivated polio vaccines are increasingly being used in those countries in which poliomyelitis has been brought under control; however, live vaccines are still the most widely used types and the World Health Organization (WHO) have set the goal of using such vaccines to eliminate the wild-type virus throughout the world by the year 2000. Substantial progress has been made to this end; however, the strains of poliovirus that are used as vaccines are able to adapt rapidly to the human gut, losing their attenuated (weakened) character within a few weeks. Currently, there is urgent debate about the best method of stopping vaccination against poliomyelitis once the wild-type poliovirus has been eliminated completely, so that the vaccine-strain virus will also be eliminated. Proposed strategies include the abrupt cessation of vaccination with the live virus worldwide, followed by the optional use of inactivated vaccines for an appropriate period. Further information about both the epidemiology and the pathogenesis of the disease is required before an informed choice can be made. The topics covered in this article include a brief history of studies of the disease, its pathogenesis and its control by vaccination, the molecular biology of the live vaccines, which have been extremely successful in controlling poliomyelitis so far, and the concerns that are raised as the eradication of the wild-type virus approaches.
HLA-B27 and disease pathogenesis: new structural and functional insights
Authors: Bowness Paul , Zaccai Nathan , Bird Lucy , Jones E. Yvonne
Published: October 2003

The human leukocyte antigen class I allele HLA-B27 is a major histocompatibility complex (MHC) antigen that is strongly associated with the spondyloarthritic group of human rheumatic diseases, the most commmon of which is ankylosing spondylitis. Although the mechanism underlying this disease association remains unknown, numerous theories have been proposed. Much more is known of the natural role of HLA-B27 in binding and presenting antigenic peptides to T cells. The ‘arthritogenic peptide hypothesis’ suggests that the role of HLA-B27 in disease relates to its specificity for binding certain peptides. Recently, it has also been shown that HLA-B27 has an unusual cell biology and can adopt a novel homodimeric structure. In this review, a molecular model of the HLA-B27 homodimer is presented and the possible pathogenic significance of such a structure is discussed.
Molecular biology and pathogenesis of hepatitis E virus
Authors: Jameel Shahid
Published: October 2003

Hepatitis E virus (HEV) infection results in hepatitis E, an acute and self-limited disease. The virus is transmitted in a faecal–oral manner and is a major cause of viral hepatitis in much of the developing world, where it causes rampant sporadic infections and large epidemics. A curious feature of hepatitis E is the unusually high rates of mortality that are observed in pregnant women, in whom the disease is exacerbated by the development of fulminant liver disease. In the absence of viable in vitro propagation systems, several geographical isolates of HEV have been maintained in vivo in nonhuman primates and, subsequently, the viral genome has been cloned and sequenced. HEV has been classified provisionally into a separate family known as the HEV-like viruses, which has at least four recognised genotypes, but has only a single serotype. The viral genome is a positive-stranded (+)RNA of ~7.5 kb and encodes at least three proteins. Open reading frame 1 (ORF1) encodes the viral nonstructural polyprotein, which has domains that are homologous to some of the replication and processing enzymes found in other +RNA viruses. The HEV protein itself remains poorly characterised. The protein encoded by open reading frame 2 (ORF2) is the major HEV capsid protein, and the protein encoded by open reading frame 3 (ORF3) appears to be involved in virus–host interactions. Several questions related to the biology, epidemiology and pathogenesis of HEV remain unanswered; the progress of a few of these is reviewed here.
Molecular genetics of human epilepsies
Authors: Bate Louise , Gardiner Mark
Published: October 2003

The term epilepsy encompasses a heterogeneous group of disorders, with a lifetime cumulative incidence of 3%. Genetic factors are thought to contribute to the aetiology in up to 60% of cases. Various molecular and cellular mechanisms give rise to epilepsy, and epilepsy genes fall into several distinct categories. They include genes in which mutations cause abnormal ion-channel function, disordered brain development, progressive neurodegeneration and disturbances of cerebral energy metabolism. In this review, we have focused on current understanding of the molecular genetic bases of human inherited epilepsies. Particular reference has been given to specific idiopathic epilepsies, neuronal migration disorders (cortical dysgeneses) and the progressive myoclonic epilepsies, and how information about this group of disorders might be used to develop new treatment strategies.
Genetic control of lifespan: studies from animal models
Authors: Van Zant Gary , de Haan Gerald
Published: October 2003

The premise that there are genes that wield a strong influence on longevity has, until recently, not been a popular one and there has been no concerted effort to find such genes. However, the finding that single genes can have large effects on the lifespans of yeast, worms and flies raises the possibility that individual genes in mammals may similarly have relatively large effects on longevity. Recent advances in mammalian genetics, many associated with the large-scale efforts to sequence the human and mouse genomes, have accelerated the search for longevity genes, principally in mice. Here, we review results using animal models that have recently shed light on genes regulating longevity and ageing patterns. A large number of genetically defined strains of mice are available and this, together with their established history of use in genetic research and their relatively short lifespans, has made murine models particularly useful. We also review our own work in which genes regulating mouse lifespan and those regulating cell cycling of haematopoietic progenitor cells have been mapped to the same locations in the genome. These results suggest that some of the same genes affect both traits, and further suggest a cause-and-effect relationship between cumulative cell-cycle activity and longevity of an organism.
Eastern margin of the Ross Sea Rift in western Marie Byrd Land, Antarctica: Crustal structure and tectonic development
Authors: Luyendyk Bruce P. , Wilson Douglas S. , Siddoway Christine S.
Published: October 2003

The basement rock and structures of the Ross Sea rift are exposed in coastal western Marie Byrd Land (wMBL), West Antarctica. Thinned, extended continental crust forms wMBL and the eastern Ross Sea continental shelf, where faults control the regional basin‐and range‐type topography at ∼20 km spacing. Onshore in the Ford Ranges and Rockefeller Mountains of wMBL, basement rocks consist of Early Paleozoic metagreywacke and migmatized equivalents, intruded by Devonian‐Carboniferous and Cretaceous granitoids. Marine geophysical profiles suggest that these geological formations continue offshore to the west beneath the eastern Ross Sea, and are covered by glacial and glacial marine sediments. Airborne gravity and radar soundings over wMBL indicate a thicker crust and smoother basement inland to the north and east of the northern Ford Ranges. A migmatite complex near this transition, exhumed from mid crustal depths between 100–94 Ma, suggests a profound crustal discontinuity near the inboard limit of extended crust, ∼300 km northeast of the eastern Ross Sea margin. Near this limit, aeromagnetic mapping reveals an extensive region of high amplitude anomalies east of the Ford ranges that can be interpreted as a sub ice volcanic province. Modeling of gravity data suggests that extended crust in the eastern Ross Sea and wMBL is 8–9 km thinner than interior MBL (β = 1.35). Gravity modeling also outlines extensive regions of low‐density (2300–2500 kg m−3) buried basement rock that is lighter than rock exposed at the surface. These regions are interpreted as bounded by throughgoing east‐west faults with vertical separation. These buried low‐density rocks are possibly a low‐density facies of Early Paleozoic metagreywacke, or the low‐density epizonal facies of Cretaceous granites, or felsic volcanic rocks known from moraines. These geophysical features and structures on land in the wMBL region preserve the record of middle and Late Cretaceous development of the Ross Sea rift. Thermochronology data from basement rocks and offshore stratigraphy suggest that the wMBL rift margin formed and most extension occurred in mid‐ and Late Cretaceous time, before seafloor spreading initiated between wMBL and the Campbell Plateau. The Cretaceous tectonic record in wMBL contrasts with the Transantarctic Mountains that form the western rift margin, where significant rift‐flank relief developed in middle Tertiary time.
Martian hydrogen exosphere charge exchange with solar wind
Authors: Chen Y. , Cloutier P. A.
Published: October 2003

Charge exchange of solar wind with the Martian exosphere has been shown to play a crucial role in the formation of the magnetic pileup boundary observed by Mars Global Surveyor. However, the question of how the Martian exospheric structure is quantitatively altered by charge exchange of the solar wind remains open. To answer this question, a three‐dimensional Monte Carlo exosphere model was developed. In this model the effects of planetary rotation, photoionization, Lyman α scattering, and charge exchange with the solar wind are included. Although the change of exospheric density profile is indistinctive, simulation results show that the existence of the hot atomic hydrogen population produced by charge exchange alters the exospheric temperature structure greatly and the symmetry of the exospheric structure is totally destroyed at high altitude. Another noticeable phenomenon is that charge exchange and Lyman α scattering combine to make the nightside exosphere be cooler than and expand more slowly than the ambient exosphere. In the end we use our simulation results to estimate the contribution of the hot component to Ly α emission. Furthermore, output of our model can be used to predict particle observations made by future missions to Mars.
Circulation of ionospheric and solar wind particle populations during extended southward interplanetary magnetic field
Authors: Winglee R. M.
Published: October 2003

Single particles trajectories using time‐dependent electric and magnetic fields from multifluid simulations are used to examine the energy and mass transport due to entry of solar wind particles and from ionospheric outflows incorporating both light and heavy ions. It is shown the particles move with the convection cells derived from the multifluid simulations, and that strong particle acceleration occurs at both the dayside and nightside tips of the flow reversal regions. However, different particle populations have limited access to various parts of the convection pattern, and this leads to substantial dawn‐dusk asymmetries in the particle populations within the magnetosphere. For the strong southward interplanetary magnetic field (IMF) conditions for the event studied, fast solar wind particles are able to enter from the dawnside and contribute to the asymmetric ring current. The rest of the fast particles flow down the mantle and do not enter the near‐Earth magnetosphere. The remaining slow component is convected into the magnetosphere over a few tens of minutes to form cold populations in the mantle and LLBL. Solar wind He++ and O6+ are shown to penetrate deeper than the solar wind protons. Light ionospheric ions from the cusp and dawnside auroral oval have similar access problems and flow primarily down the tail and make little contribution to the plasma content to the near‐Earth plasma sheet. Nightside auroral protons are shown to form a cold component in the plasma sheet boundary layer. When they are eventually convected in to the near‐Earth plasma sheet they are accelerated preferentially to the duskside and experience further energy gains as they are convected sunward. These energetic protons contribute to the asymmetric ring current, with leakage from the magnetosphere occurring as they approach the dayside reconnection region. Heavy ionospheric ions enter the convection pattern differently from their light ions counterparts. O+ ions from the cusp can enter the near‐Earth plasma sheet to provide some mass loading, but the biggest contributor is the dawnside auroral oval. The dawn‐dusk electric field accelerates these ions toward the dusk side, but on sufficient low L shells that these ions can dominate the symmetric ring current composition. The O+ ions that originate from the midnight and dusk sectors go to forming hot populations in the dusk LLBL.
Dissolution/precipitation mechanisms for diagenesis in sedimentary basins
Authors: Fowler A. C. , Yang Xin‐She
Published: October 2003

The transformation of hydrated clay minerals (smectite) to anhydrous forms (illite) occurs in the diagenesis of shales in sedimentary basins. The released pore water can lead to excess pore pressures and is of concern in oil drilling operations. Most simply, the process can be modeled as a first‐order thermally activated reaction, but an alternative interpretation is that diagenesis occurs via dissolution of smectite in free pore water and subsequent precipitation of illite. We show how such a realistic model of diagenesis can be included in a compactive model of the sediment/pore water system, and by using the limit of weak solubility (also known as solid density asymptotics), we show how an explicit expression can be derived for the smectite dissolution rate, even when this is mediated by feldspar dissolution and other reactions. In certain circumstances, the reaction rate reduces to that of a simple first‐order model. By solving the model we also show that shale diagenesis provides a mechanism for the generation of fractures at depth in rapidly deposited sediments. When sedimentation is slow (or compaction is fast), the smectite to illite transition occurs over a reaction window which typically lies below the equilibrated normally pressured part of the profile, but it does not generally contribute significantly to the overpressuring.
On the generation of secondary microseisms observed in northern and central Europe
Authors: Essen Heinz‐Hermann , Krüger Frank , Dahm Torsten , Grevemeyer Ingo
Published: October 2003

Microseism recordings from four European broadband stations and from three seismic arrays in Scotland, Norway, and Germany are compared with model wave data of the oceanic wave field in the North Atlantic and local ocean wave data from the Norwegian coast at 60°N, both measured during February–March 2000. Two approaches have been tested to locate generation areas of microseismic energy: a new amplitude correlation technique and beam backprojection from the three seismic arrays. Both techniques reveal that the main generation areas are located in specific regions off the coast of Southwest Norway and North Scotland. Seismic stations distant from these generation areas record a superposition of seismic energy from different source regions. Those close to a specific source region also show a high correlation with it. Both techniques give upper limits for the extent of the generation area of the strongest storm on 6/7 March at the southwest Norwegian coast of about 500 km. By using marine X‐band radar measurements of the two‐dimensional wave height spectrum, we estimate that the relative change of the extension of the generation area off the coast of southwest Norway during several storms is less than a factor of 3. This indicates that the size of the generation area is controlled by static features as coastline or bathymetry, and not by the extent of the storms. Microseism energy appears to be mainly controlled by the wave height in distinct and identifiable generation regions, so that the wave climate in these regions can be studied using historical records of microseisms.
Predicting benthic fluxes of silicic acid from deep‐sea sediments
Authors: Dixit Suvasis , Van Cappellen Philippe
Published: October 2003

Benthic fluxes of silicic acid are driven by the dissolution of biogenic opal deposited at the seafloor. The fluxes vary over several orders of magnitude and correlate inversely with the mass ratio of lithogenic matter to biogenic opal of the sediments. The role of the lithogenic, or detrital, sediment fraction was studied in batch reactors, by monitoring the release of silicic acid from mixtures of a well‐characterized biosiliceous ooze from the Southern Ocean and model lithogenic materials (kaolinite or basalt). The rate constant of silicic acid production and the saturation silicic acid concentration decreased systematically with increasing detrital to opal mass ratio of the mixtures. Both effects, which are attributed to the release of soluble aluminum from lithogenic mineral phases, were incorporated into an early diagenetic model to calculate diffusive benthic silicic acid fluxes from deep‐sea sediments. The apparent silica dissolution rate constant, the saturation (or asymptotic) pore water silicic acid concentration, and the concentration of biogenic opal were the critical parameters determining the model‐derived benthic fluxes. Predicted benthic fluxes of silicic acid were compared to values reported for deep‐sea sediments with known detrital to opal ratio and asymptotic pore water concentration. When taking into account the dependence of pore water silicic acid build up on the detrital sediment fraction, good agreement was found between predicted and measured benthic fluxes, over a wide range of oceanic areas and sediment composition, from opal rich to opal poor sediments. The model provides a means to estimate the benthic flux of silicic acid for deep‐sea sediments for which the asymptotic silicic acid concentration and the composition of the uppermost sediment are known.
Diurnal variation in the concentration of air ions of different mobility classes in a rural area
Authors: Hõrrak Urmas , Salm Jaan , Tammet Hannes
Published: October 2003

Analyzed data consist of 8900 hourly average mobility distributions measured in the mobility range of 0.00041–3.2 cm2 V−1 s−1 (diameter range 0.36–79 nm) at Tahkuse Observatory, Estonia, in 1993–1994. The average diurnal variation in the concentration of cluster ions is typical for continental stations: the maximum in the early morning hours and the minimum in the afternoon. This is explained by variations in radon concentration. The diurnal variation for big cluster ions (0.5–1.3 cm2 V−1 s−1) differs from that for small cluster ions (1.3–3.14 cm2 V−1 s−1). The size distribution of intermediate and light large ions in the range of 1.6–22 nm is strongly affected by nucleation bursts of nanometer particles. On the burst days, the maximum concentration of intermediate ions (1.6–7.4 nm) is about the noontime and that of light large ions (7.4–22 nm) about 2 hours later. The concentration of heavy large ions (charged Aitken particles of diameters of 22–79 nm) is enhanced in the afternoon and this is explained by the bursts of nanometer particles and the subsequent growth of particles by condensation and coagulation. If the burst days are excluded, then in the warm season the concentration of Aitken particles increases during night. In the cold season, the diurnal variation is different and all the classes of aerosol ions (2.1–79 nm) show similar variation with the minimum at 0600 LT and the maximum in the afternoon; exceptions are the rare nucleation burst days.
Measurements of large stratospheric particles in the Arctic polar vortex
Authors: Brooks Sarah D. , Baumgardner Darrel , Gandrud Bruce , Dye James E. , Northway Megan J. , Fahey David W. , Bui T. Paul , Toon Owen B. , Tolbert Margaret A.
Published: October 2003

During the SAGE III Ozone Loss and Validation Experiment/Third European Stratospheric Experiment on Ozone 2000 mission, the Multiangle Aerosol Spectrometer Probe (MASP) was flown aboard the ER‐2 aircraft sampling the Arctic polar vortex. On several of the flights the ER‐2 flew directly through polar stratospheric clouds (PSCs), and on six of these flights the MASP sampled large particles (2–22 μm diameter). MASP large particle observations are correlated in time with the large particle signal from the NOAA NOy measurements. This is direct evidence supporting the inference of particle size made by the NOy instrument. On 20 January 2000, the day of the most intense PSC encounter, the shapes of the large particle size distributions above 9 μm observed by the MASP and simulated based on the NOy instruments are in reasonable agreement. The MASP observations show a dramatic increase in large particle volume as the temperature approaches the nitric acid trihydrate equilibrium temperature. Our study suggests that large particles containing nitric acid are present in the Arctic polar stratosphere and may lead to denitrification.
Paleomagnetic definition of crustal fragmentation and Quaternary block rotations in the east Ventura Basin and San Fernando valley, southern California
Authors: Levi Shaul , Yeats Robert S.
Published: October 2003

Paleomagnetic studies of the Pliocene‐Quaternary Saugus Formation in the eastern part of the western Transverse Ranges of California show that the crust is fragmented into small domains, tens of kilometers in linear dimension, identified by rotation of reverse‐fault blocks. In an area approximately 35 × 25 km in the San Fernando valley and east Ventura Basin we identified four distinct domains. Two domains, southwest of and adjacent to the San Gabriel fault, are rotated clockwise: (1) The Magic Mountain domain, R = 30° ± 5° and (2) the Merrick syncline domain, R = 34° ± 6°. The Magic Mountain domain has rotated since 1 Ma. Both rotated sections occur in hanging walls of active reverse faults, the Santa Susana and San Fernando faults, respectively. Structural data suggest that the fault tip of the Santa Susana fault is the rotation pivot of the Magic Mountain domain. Two additional blocks are unrotated: (1) the Van Norman Lake domain, directly south of the Santa Susana fault, and (2) the Soledad Canyon domain, immediately across the San Gabriel fault from the Magic Mountain domain, suggesting that the San Gabriel fault might be a domain boundary. Our results suggest that part of the clockwise rotation of some Miocene and older rocks in this area might have occurred in the Quaternary. The Plio‐Pleistocene fragmentation and clockwise rotations continue at present, based on geodetic data, and represent crustal response to diffuse, oblique dextral shearing within the San Andreas fault system.
Characteristic space scales and timescales in hydrology
Authors: Skøien J. O. , Blöschl G. , Western A. W.
Published: October 2003

We analyzed spatial and temporal variograms of precipitation, runoff, and groundwater levels in Austria to examine whether characteristic scales exist and, if so, how big they are. In time, precipitation and runoff are stationary with characteristic scales on the order of a day and a month, respectively, while groundwater levels are nonstationary. In space, precipitation is almost fractal, so no characteristic scales exist. Runoff is nonstationary but not a fractal as it exhibits a break in the variograms. An analysis of the variograms of catchment precipitation indicates that this break is due to aggregation effects imposed by the catchment area. A spatial variogram of hypothetical point runoff back calculated from runoff variograms of three catchment size classes using aggregation statistics (regularization) is almost stationary and exhibits shorter characteristic space scales than catchment runoff. Groundwater levels are nonstationary in space, exhibiting shorter‐scale variability than precipitation and runoff, but are also not fractal as there is a break in the variogram. We suggest that the decrease of spatial characteristic scales from catchment precipitation to runoff and to groundwater is the result of a superposition of small‐scale variability of catchment and aquifer properties on the rainfall forcing. For comparison, TDR soil moisture data from a comprehensive Australian data set were examined. These data suggest that in time, soil moisture is close to stationary with characteristic scales of the order of 2 weeks while in space soil moisture is nonstationary and close to fractal over the extent sampled. Space‐time traces of characteristic scales fit well into a conceptual diagram of Blöschl and Sivapalan [1995]. The scaling exponents z in T ∼ Lz (where T is time and L is space) are of the order of 0.5 for precipitation, 0.8 for runoff from small catchments, 1.2 for runoff from large catchments, 0.8 for groundwater levels, and 0.5 for soil moisture.
Interaction between the Mid‐Atlantic Ridge and the Azores hot spot during the last 85 Myr: Emplacement and rifting of the hot spot‐derived plateaus
Authors: Gente Pascal , Dyment Jérôme , Maia Marcia , Goslin Jean
Published: October 2003

Multiple‐ and single‐beam bathymetric data are compiled over the Azores plateau to produce a 1 km × 1 km grid between latitudes 32°N and 49°N and longitudes 22°W and 43°W. Mantle Bouguer anomalies are then calculated from this grid and the satellite‐derived gravity. These grids provide new insights on the temporal and spatial variations of melt supply to the ridge axis. The elevated seafloor of the Azores plateau is interpreted as resulting from the interaction of a mantle plume with the Mid‐Atlantic Ridge (MAR). The presence of a large region of elevated seafloor associated with a thick crust between the Great Meteor Seamounts and the Azores platform on the Africa plate, and less developed conjugate structures on the North America plate, favors genetic relations between these hot spot‐derived structures. This suggests that a ridge‐hot spot interaction has occurred in this region since 85 Ma. This interaction migrated northward along the ridge axis as a result of the SSE absolute motion of the Africa plate, following a direction grossly parallel to the orientation of the MAR. Kinematic reconstructions from chron 13 (∼35 Ma) to the present allow a proposal that the formation of the Azores plateau began around 20 Ma and ended around 7 Ma. A sharp bathymetric step is associated with the beginning of important melt supply around 20 Ma. The excess of melt production is controlled by the interaction of the ridge and hot spot melting zones. The geometry and distribution of the smaller‐scale features on the plateau record episodic variations of the hot spot melt production. The periodicity of these variations is about 3–5 Myr. Following the rapid decrease of widespread volcanism, the plateau was subsequently rifted from north to south by the Mid‐Atlantic Ridge since 7 Ma. This rifting begins when the MAR melting zone is progressively shifted away from the 200‐km plume thermal anomaly. These results bear important consequences on the motion of the Africa plate relative to the Azores hot spot. They also provide an explanation to the asymmetric geochemical signature of the Azores hot spot along the Mid‐Atlantic Ridge.
Substorm associated changes in the high‐latitude ionospheric convection
Authors: Jayachandran P. T. , MacDougall J. W. , Donovan E. F. , Ruohoniemi J. M. , Liou K. , Moorcroft D. R. , St‐Maurice J.‐P.
Published: October 2003

A study of polar cap/dayside convection response to substorm intervals using Canadian Advanced Digital Ionosondes (CADIs), situated well within the polar cap, and SuperDARN radars during steady and prolonged southward IMF Bz conditions showed three distinct features: (1) gradual prolonged decrease of dayside/polar cap convection speed until the substorm onset; (2) sudden decrease of convection following the onset of the substorm; and (3) increase of convection during the recovery phase of the substorm. We hypothesize that the observed features of the convection are due to the modulation of the Region 1 current system associated with the substorm. The ground magnetic response of magnetometers situated inside the polar cap is at least consistent with our postulate.
Force‐free field inside a toroidal magnetic cloud
Authors: Romashets E. P. , Vandas M.
Published: October 2003

An analytical solution of force‐free magnetic fields inside a toroid with an arbitrary aspect ratio was found. A scalar equation was derived which when solved gives the heart of the solution of the vector field in toroidal coordinates, in closed form in terms of hypergeometric functions. The solution can be used for interpretation of magnetic cloud measurements in the interplanetary space. If it is assumed that a magnetic cloud is a large loop with roots at the Sun, then its part can be locally treated as a part of a toroid. The former solution by Miller and Turner [1981] was limited only to larger aspect ratios. The presented solution coincides with the Lundquist [1950] one for cylindrical clouds in case of a very large aspect ratio torus.
Relationship between the Tibetan Plateau heating and East Asian summer monsoon rainfall
Authors: Hsu Huang‐Hsiung , Liu Xin
Published: October 2003

This study reveals the close correspondence between the interannual variability of the dominant East Asian summer rainfall pattern and the diabatic heating over the Tibetan Plateau in both spring and summer. The heating fluctuation over the Tibetan Plateau is associated with two wave‐like circulation patterns, which bear the characteristics of forced Rossby wave emanating away from the deep heating. The wave‐like pattern in turn affects the East Asian summer rainfall. Because of the persistent heating over the Tibetan Plateau from spring to summer and its possible effect on the surrounding areas, the heating index defined in this study can be used as a good predictor for the JJA heating and precipitation distributions. Evidences shown suggest that external conditions other than the SST anomaly must be considered to understand the interannual variability of the East Asian summer rainfall.
Båth's law derived from the Gutenberg‐Richter law and from aftershock properties
Authors: Helmstetter Agnès , Sornette Didier
Published: October 2003

The empirical Båth's law states that the average difference in magnitude between a mainshock and its largest aftershock is 1.2, regardless of the mainshock magnitude. Following Vere‐Jones' [1969] and Console et al. [2003], we show that the origin of Båth's law is to be found in the selection procedure used to define mainshocks and aftershocks rather than in any difference in the mechanisms controlling the magnitude of the mainshock and of the aftershocks. We use the ETAS model of seismicity, which provides a more realistic model of aftershocks, based on (i) a universal Gutenberg‐Richter (GR) law for all earthquakes, and on (ii) the increase of the number of aftershocks with the mainshock magnitude. Using numerical simulations of the ETAS model, we show that this model is in good agreement with Båth's law in a certain range of the model parameters.
Airborne measurements of gravity wave breaking at the tropopause
Authors: Whiteway James A. , Pavelin Edward G. , Busen Reinhold , Hacker Jorg , Vosper Simon
Published: October 2003

A breaking atmospheric gravity wave was investigated with a combination of airborne in‐situ dynamical measurements and ground‐based VHF radar observations. The wave was generated by flow over mountains and it was observed to break near the tropopause. The measurements reveal that the wave was overturning at the tropopause and that the initial breakdown into turbulence involved the generation of smaller oscillations with a horizontal wavelength of around 500 m. There was also evidence that the turbulence associated with the wave breaking can cause substantial mixing in the tropopause region.
A new method of measuring 81Kr and 85Kr abundances in environmental samples
Authors: Du X. , Purtschert R. , Bailey K. , Lehmann B. E. , Lorenzo R. , Lu Z.‐T. , Mueller P. , O'Connor T. P. , Sturchio N. C. , Young L.
Published: October 2003

We demonstrate a new method for determining the 81Kr/Kr ratio in environmental samples based upon two measurements: the 85Kr/81Kr ratio measured by Atom Trap Trace Analysis (ATTA) and the 85Kr/Kr ratio measured by Low‐Level Counting (LLC). This method can be used to determine the mean residence time of groundwater in the range of 105–106 a. It requires a sample of 100 μl STP of Kr extracted from approximately two tons of water. With modern atmospheric Kr samples, we demonstrate that the ratios measured by ATTA and LLC are directly proportional to each other within the measurement error of ±10%; we calibrate the 81Kr/Kr ratio of modern air measured using this method; and we show that the 81Kr/Kr ratios of samples extracted from air before and after the development of the nuclear industry are identical within the measurement error.
Diurnal variation of precipitation by moving mesoscale systems: Radar observations in northern Thailand
Authors: Okumura K. , Satomura T. , Oki T. , Khantiyanan Warawut
Published: October 2003

The diurnal cycle of radar echo data observed at Om Koi, northern Thailand, during three rainy seasons (May to October, 1998, 1999 and 2000) are analyzed. From May to July when southwesterly monsoons blow over the observation area, the diurnal cycles in the leeward regions (inland of Thailand) show a phase delay that corresponds to the distance from the mountains. In October when the wind direction reverses and blows from the east or northeast, inland regions correspond to the upwind side of the mountains and do not show clear phase shifts. The regions near the coast of the Andaman Sea, which is the leeward in October, show a similar phase shift of the diurnal cycle as the inland area during May–July. The echo tracking analysis reveals that echoes, which are triggered near the mountains and moved to leeward regions, caused phase delays, which depended on the lee distance.
Anomalous cosmic ray intensity variations in the inner and outer heliosphere during the solar cycle 22 recovery phase (1991–1999)
Authors: Hill M. E. , Hamilton D. C. , Mazur J. E. , Krimigis S. M.
Published: October 2003

Differential intensity measurements of interplanetary H, He, and O ions made with the Low‐Energy Charged Particle (LECP) instruments aboard the Voyager 1 (V1) and Voyager 2 (V2) deep space probes and the Low‐Energy Ion Composition Analyzer (LICA) aboard the near‐Earth Solar Anomalous Magnetospheric Particle Explorer (SAMPEX) satellite provide a comprehensive perspective on the transport of anomalous cosmic ray (ACR) ions during the 1991–1999 recovery phase of solar cycle 22 in both the outer and inner heliosphere. We report fifteen unique, independent ACR intensity time series, ranging over kinetic energies from 0.6 to 40 MeV/nucleon, and parameterize these observations (supplemented by one time‐intensity profile from the literature) with a four‐parameter fitting function to quantify the ACR behavior as solar minimum conditions developed and the V1 and V2 probes ranged from 36 to 76 AU from the Sun. We discuss a possible physical explanation for the striking differences between the outer heliospheric ACR recovery profiles at various energies. The intensities of nearly all species and energies recovered similarly from 1991 to mid‐1994, increasing about an order of magnitude, but differed in a rigidity‐dependent manner during the subsequent 5 years with the low‐rigidity particle intensities growing exponentially, increasing up to an order of magnitude, while the high‐rigidity particle intensities remained nearly constant. We find that these observations support the interpretation that before 1994 the recovery profiles of all the ACRs were governed by a temporal mechanism probably driven by the timescale of the variation of the transport properties of the interplanetary medium itself, rather than the “relaxation” timescale for diffusive equilibrium to develop. After 1994 the motion of the Voyager probes through regions with stable, positive radial intensity gradients explains the diverse recovery profiles of the various ACR species.
In situ observations during an HF heating experiment at Arecibo: Evidence for Z‐mode and electron cyclotron harmonic effects
Authors: Gelinas L. J. , Kelley M. C. , Sulzer M. P. , Mishin E. , Starks M. J.
Published: October 2003

On 11 March 1998 the Langmuir Turbulence sounding rocket was launched through the Arecibo heater beam during an experiment to measure electric fields and plasma densities in the heater interaction region. In spite of a serious degradation of the Arecibo heater, the rocket data has provided evidence of Z mode waves and field aligned striations above the O mode reflection height. These observations give credence to the theory that Z mode wave interactions with field‐aligned striations may be, in part, responsible for some of the features of the reflected HF spectrum observed in heating experiments. We also find strong low‐frequency electric fields where the local plasma frequency matches an electron cyclotron harmonic. This suggests that electron Bernstein modes must be generated in the interaction process and can propagate to regions where they are severely damped.
Modeling day‐to‐day ionospheric variability on Mars
Authors: Martinis Carlos R. , Wilson Jody K. , Mendillo Michael J.
Published: October 2003

We use a simple photochemical model of Mars' ionosphere to investigate the changes in calculated electron density profiles, Ne(h), under the assumption that the only variable parameter is the solar irradiance. The period under study is 9–27 March 1999, corresponding to a series of Ne(h) observations made by the Mars Global Surveyor (MGS) Radio Science (RS) experiment. The SOLAR 2000 model is used to obtain the solar irradiances during this period. Secondary ionization is included and is expressed as a simple function of photoionization. The model uses several neutral gas species, five of which (CO2, N2, CO, NO, O) experience photoionization. Subsequent ion‐neutral chemistry leads to an ionosphere with five ions species. Using average solar conditions for March 1999, good agreement was obtained between the model's mean electron density profile and the mean electron densities from the MGS observations. Modeling day‐to‐day changes using daily solar irradiance values resulted in ∼6% and 19% variabilities for the major and secondary layer peak densities, respectively, in good agreement with the observed values of 5 and 10%. The variable photon flux from the Sun is thus the primary driver of day‐to‐day changes in the peak electron densities on Mars.
A measure from line‐of‐sight magnetograms for prediction of coronal mass ejections
Authors: Falconer D. A. , Moore R. L. , Gary G. A.
Published: October 2003

From a sample of 17 vector magnetograms of 12 bipolar active regions we have recently found (1) that a measure of the overall nonpotentiality (the overall twist and shear in the magnetic field) of an active region is given by the strong shear length LSS, the length of the portion of the main neutral line on which the observed transverse fields is strong (>150 Guass (G)) and strongly sheared (shear angle >45°), and (2) that LSS is well correlated with the coronal mass ejection (CME) productivity of the active regions during the ±2‐day time window centered on the day of the magnetogram. In the present paper, from the same sample of 17 vector magnetograms, we show that there is a viable proxy for LSS that can be measured from a line‐of‐sight magnetogram. This proxy is the strong gradient length LSG, the length of the portion of the main neutral line on which the potential transverse field is strong (>150 G), and the gradient of the line‐of‐sight field is sufficiently steep (greater than ∼50 G/Mm). In our sample of active regions, LSG is statistically significantly correlated with LSS (correlation confidence level >95%), and LSG is as strongly correlated with active region CME productivity as is LSS (correlation confidence level ∼99.7%). Because LSG can be measured from line‐of‐sight magnetograms obtained from conventional magnetographs, such as the magnetograph mode of the Michelson Doppler Imager (MDI) on board the Solar and Heliospheric Observatory, it is a dependable substitute for LSS for use in operational CME forecasting. In addition, via measurement of LSG, the years‐long, nearly continuous sequence of 1.5‐hour cadence full disk line‐of‐sight magnetograms from MDI can be used to track the growth and decay of the large‐scale nonpotentiality in active regions and to examine the role of this evolution in active region CME productivity.
Deep sea NMR: Methane hydrate growth habit in porous media and its relationship to hydraulic permeability, deposit accumulation, and submarine slope stability
Authors: Kleinberg R. L. , Flaum C. , Griffin D. D. , Brewer P. G. , Malby G. E. , Peltzer E. T. , Yesinowski J. P.
Published: October 2003

Review of the literature reveals that the nature of pore‐scale interactions between gas hydrates and porous media remains a matter of controversy. To clarify the situation, nuclear magnetic resonance (NMR) measurements have been made on methane hydrate‐bearing sandstones. The samples were synthetically prepared within the gas hydrate stability zone, at or near the seafloor in Monterey Bay, California. The method simulated natural hydrate deposition by gas flows that are not in thermodynamic equilibrium with the surrounding earth. The efficiency of hydrate production was variable, as has been observed elsewhere. When substantial hydrate saturations were achieved, NMR relaxation time measurements indicated that hydrate tended to replace water in the largest pore spaces. The relative permeability to water, as determined by an NMR‐based correlation, was significantly reduced. The magnitude of this reduction was also consistent with formation of hydrate in the centers of pores, rather than with hydrate coating the grains. The growth habit suggested by these results is consistent with creation of hydrate nodules and lenses in coarse, unconsolidated sediments. It is also consistent with scenarios in which methane gas is delivered efficiently to the atmosphere as a result of seafloor slope failure, thereby strengthening global warming feedback mechanisms.
Simulation of dissolution and precipitation in porous media
Authors: Kang Qinjun , Zhang Dongxiao , Chen Shiyi
Published: October 2003

We apply the lattice‐Boltzmann method to simulate fluid flow and dissolution and precipitation in the reactive solid phase in a porous medium. Both convection and diffusion as well as temporal geometrical changes in the pore space are taken into account. The numerical results show that at high Peclet and Peclet‐Damkohler numbers, a wormhole is formed and permeability increases greatly because of the dissolution process. At low Peclet and high Peclet‐Damkohler numbers, reactions mainly occur at the inlet boundary, resulting in the face dissolution and the slowest increase of the permeability in the dissolution process. At moderate Peclet and Peclet‐Damkohler numbers, reactions are generally nonuniform, with more in the upstream and less in the downstream. At very small Peclet‐Damkohler number, dissolution or precipitation is highly uniform, and these two processes can be approximately reversed by each other. These numerical examples have not been yet confirmed by physical experimentation. Nevertheless, we believe that these simulation results can serve to estimate the effects of dissolution and precipitation during reactive fluid flow.
Influence of interannual rainfall anomalies on sea level variations in the tropical Indian Ocean
Authors: Perigaud Claire , McCreary Julian P.
Published: October 2003

A halo‐thermal, reduced‐gravity model with four active layers is used to investigate how interannual rainfall anomalies affect sea surface height (SSH) variability in the Indian Ocean. The model is forced by monthly varying winds observed over the period 1980–2000 in two experiments that differ by their rainfall forcing, Run FSU and Run Arkin, forced by climatological and interannually varying rainfall, respectively. Compared to the large impact of wind on SSH (about 30 cm), the impact of rain is much smaller. Its maximum (found in the southeastern Indian Ocean during the rainfall deficits of 1994 and 1997) is only 2 cm. Because rainfall significantly affects model salinity and temperature, the deficits make the layers of Run Arkin colder and saltier than in Run FSU, causing a −5 cm change in sea level. Baroclinic adjustments also occur such that the top (bottom) two layers are thicker (thinner), increasing sea level by 3 cm and hence significantly reducing the SSH change due to steric effects alone. SSH variability in either Run Arkin or Run FSU compares very well with TOPEX data. Although the impact of rainfall on SSH is negligible, salinity variations significantly affect dynamic‐height calculations of SSH. In the model, the neglect of salinity variations leads to an error of 5 to 10 cm along the eastern boundary, in the Bay of Bengal, and in the interior ocean south of 8°S. This error is validated by the difference between TOPEX data and SSH derived from observed temperature profiles.
Seasonal and interannual variation in water vapor and heat fluxes in a West Siberian continental bog
Authors: Shimoyama K. , Hiyama T. , Fukushima Y. , Inoue G.
Published: October 2003

The seasonal and interannual variation in the energy fluxes of a West Siberian continental bog were measured from April to October in 1999 and 2000 using the eddy covariance method. The energy balance closure rate (=[sensible + latent heat fluxes]/[available energy]) ranged from ∼0.8 to 0.9 and showed a better energy balance and less scattering using the soil heat flux estimated from an area‐averaged soil thermal parameter rather than from a plot‐based measurement. The net radiation (Rn) increased drastically after snowmelt because the surface albedo (a) dropped from its highest value to its lowest value over the course of the snowmelt. The snowmelt water raised the water table (zwt) to its highest level; it then gradually decreased. The seasonal and interannual variation in a, which ranged from 0.09–0.19, depended on zwt, because surface wetness was closely related to zwt through the capillary uptake of Sphagnum moss. The seasonal variation in the latent heat flux (lE) was similar to that in Rn. The largest lE was observed in the middle of June, and was ∼120 Wm−2 (4.2 mm d−1) in both years. Conversely, the sensible heat flux (H) did not show an obvious seasonal pattern and was lower than lE during the growing season. The Bowen ratio (Br) in the early growing season was 0.57 and 0.60, and the values in the peak growing season were 0.65 and 0.78, in 1999 and 2000, respectively. The lower Br was related to the higher zwt; specifically, it was due to the wetter surface conditions. An interannual comparison of the monthly mean atmospheric water vapor deficit (δe) and lE showed a significant relationship with a higher lE observed in the year with a higher δe. Therefore in the bog studied the interannual variation in the water vapor flux was controlled mainly by zwt and δe.