biogenic sedimentation and geochemical properties of deep sea sediments of the demerara slope abyssal plain influence of the amazon river plume abstract the amazon river plume has a major impact on sedimentation at abyssal depths throughout a broad area 450 000 km2 and far 500 1000 km from the river mouth as the plume mixes into the north atlantic ocean it may support ecological niches favorable for n2 fixation driven by the symbiosis between diatoms and diazotrophic cyanobacteria this proposed diatom diazotroph association dda should result in increased carbon export from a limited region of plume influence here we used 32 multicores collected throughout the demerara abyssal slope and plain at depths ranging from 3000 to 5000m to assess patterns and rates of export and accumulation of organic carbon corg or poc and biogenic sio2 bsi sediment accumulation rates were determined from 14c ages of foraminifera obtained at 2 5 depths from 9 cores and were further constrained by 230th measurements the sedimentation rate 1 5 cm ky 1 representing the average accumulation over the past 8000 years was combined with corg and bsi sediment concentrations to establish biogenic matter burial fluxes burial of poc represents 4 16 of the corg raining to the deep sea floor which is high for water depths 4000 m burial of bsi represents 1 9 of the total bsi rain clastic sedimentation dominates regions underlying the plume while carbonate sedimentation dominated otherwise sediment mixing bioturbation was studied in 13 cores using 210pb as a tracer and showed no spatial patterns diffusional mixing coefficients ranged from 0 03 to 3 2 cm year 1 values consistent with other deep sea mixing rates however sites with the highest mixing rates did not have the highest corg content sediment focusing was studied in at 7 sites using 230th as a tracer surficial sediments had focusing factors that ranged from 1 to 2 indicating little sediment redistribution biogenic sedimentation in general and bsi deposition in particular is not concentrated in the region of dda abundance the nw axis of primary plume trajectory is coincident with the maximum deposition and burial of poc and bsi but not caco3

tectonic history of the north portion of the san andreas fault system california inferred from gravity and magnetic anomalies geologic and geophysical data for the san andreas fault system north of san francisco suggest that the eastern boundary of the pacific plate migrated eastward from its presumed original position at the base of the continental slope to its present position along the san andreas transform fault by means of a series of eastward jumps of the mendocino triple junction these eastward jumps total a distance of about 150 km since 29 ma correlation of right laterally displaced gravity and magnetic anomalies that now have components at san francisco and on the shelf north of point arena indicates that the presently active strand of the san andreas fault north of the san francisco peninsula formed recently at about 5 ma when the triple junction jumped eastward a minimum of 100 km to its present location at the north end of the san andreas fault prior to 5 ma the triple junction was located at the north end of a proposed northwesterly extension of the pilarcitos fault this jump took place at what is now about latitude 38 20 n on the north american plate and may have occurred during part of the time when the relative motion between the north american and pacific plates rotated 20 clockwise resulting in transpression along the earlier transcurrent san andreas fault system the proposed 150 km eastward movement of the triple junction explains the submarine topography near cape mendocino where the continental shelf south of the mendocino fault extends about 130 km farther west than does the shelf directly north of the fault

microphysical characteristics of overshooting convection from polarimetric radar observations the authors present observations of the microphysical characteristics of deep convection that overshoots the altitude of the extratropical tropopause from analysis of the polarimetric radar variables of radar reflectivity factor at horizontal polarization zh differential reflectivity zdr and specific differential phase kdp identified overshooting convective storms are separated by their organization and intensity into three classifications organized convection discrete ordinary convection and discrete supercell convection composite analysisof identifiedstorms foreach classification reveals microphysical featuressimilar tothose found inpreviousstudiesofdeepconvection withdeepcolumnsofhighlypositivezdrandkdprepresentinglofting of liquid hydrometeors within the convective updraft and above the melting level in addition organized and discrete supercell classifications show distinct near zero zdr minima aligned horizontally with and at altitudes higher than the updraft column features likely indicative of the frequent presence of large hail in each case composites for organized convective systems show a similar zdr minimum throughout the portion of the convective core that is overshooting the tropopause corresponding to zh in the range of 15 30dbz and negative kdp observations in agreement with the scattering properties of small hail and or lump or conical graupel additional analyses of the evolution of overshooting storms reveals that the zdr minima indicative of hail in the middle and upper troposphere and graupel in the overshooting top are associated with the mature and decaying stages of overshooting respectively supporting their inferred contributions to the observed polarimetric fields

archaeological site surveying program at the university of nebraska a summary of geophysical applications peculiar to archaeology and magnetic surveying techniques applied by the university of nebraska to archaeological sites is presented in contrast to geophysical targets the size and depth of the features of interest on archaeological sites are from several centimeters to a few meters typical features are historic foundations wells privies or prehistoric earthen features such as earth house floors storage pits or fire hearths the most commonly used geophysical methods are resistivity radar and magnetometry the program at the university of nebraska has concentrated on magnetic surveying field methods based on the use of two magnetometers in the difference mode to correct for temporal variations data processing used both microcomputers and mainframe computers microcomputers are used in the field and near sites to log data and to do preliminary mapping mainframe computers are used for further processing and filtering and for producing a variety of graphical r

numerical simulation of the effects of mesoscale convergence on convective rain showers abstract a nonhydrostatic axisymmetric cloud model is used to quantify the effects of persistent mesoscale convergence on cumulus development and convective rainfall the model was initialized by environmental conditions adopted from sounding and doppler radar velocity data sampled on 19 august 1992 in central alberta the sounding showed a moist warm air mass with a moderate amount of convective available potential energy and the wind field had boundary layer convergence but almost no vertical shear in the lowest 5 km the simulated rainfall intensity and accumulation compared well with radar observations the dependence of the convective rainfall on the characteristics of the convergence zone is investigated by intercomparing model simulators with different convergence magnitudes convergence depths and convergence profiles increasing the magnitude or the depth of convergence causes stronger convection and more precipitation rainfall increases monotonically but nonstrictly linearly with the converg

kinematic microphysical and electrical aspects of an asymmetric bow echo mesoscale convective system observed during steps 2000 1 five hours of detailed observations of the asymmetric bow echo mesoscale convective system on 11 12 june 2000 during the steps project are presented data sources included polarimetric and doppler radars a vhf lightning mapper and the national lightning detection network nearly every 99 vhf lightning source occurred within 10 km of the convective line charge identification within the much of the convective line revealed evolution during the first 3 h from a normal polarity dipole upper positive charge near 9 km msl 30 c over mid level negative charge near 7 km 16 c to a normal polarity tripole with the addition of lower positive charge near 4 km 1 c during the final 2 h the charge structure resembled an inverted dipole with negative charge overlaying positive when the bow echo occurred during hour 2 part of the cells associated with severe winds developed an inverted tripolar charge structure and produced predominantly positive cloud to ground lightning stratiform lightning was infrequent normally initiating in the convective line and propagating rearward along two pathways a downward sloping upper pathway near 9 km and a more common constant altitude lower pathway near 6 km 10 c some flashes initiated within the stratiform region during this time but only after stratiform reflectivities increased significantly in the mixed phase region these flashes initiated near the bright band 4 km and tapped negative charge above and positive charge below possible mechanisms to explain the observations are discussed

constraints on the crustal nature and tectonic history of the kerguelen plateau from comparative magnetic modeling using magsat data abstract the kerguelen plateau in the southern indian ocean is associated with the broken ridge plateau because of their location with respect to the southeast indian ridge the kerguelen plateau lies south of the mid ocean ridge and the broken ridge plateau is located at a nearly equal distance to the north both plateaus have positive magsat crustal magnetic anomalies associated with them comparative modeling of these anomalies places constraints on the crustal nature the thermal structure and the tectonic history of the plateaus our results support the theory that both plateaus are underlain by oceanic crust are structurally and lithologically similar and were formed as a single structure which has since been split by seafloor spreading active volcanoes on the northern part of the kerguelen plateau suggest that it lies on a hotspot which has raised the curie isotherm to within the crust of the plateau decreasing the crustal volume contributing to the magnetic anomaly and thus decreasing the amplitude of the anomaly

three dimensional kinematic and microphysical evolution of florida cumulonimbus part i spatial distribution of updrafts downdrafts and precipitation abstract this paper is the first in a three part study that examines the kinematic and microphysical evolution of florida cumulonimbus and focuses on the convective to stratiform transition of the storm this first paper lays the groundwork for the subsequent papers by defining the problem under study delineating the setting for the storm and describing the spatial distribution of updrafts downdrafts and precipitation high resolution radar data of a typical line of storms associated with the florida sea breeze is the centerpiece of this study the high resolution data reveal details of the internal structure of the squall line that were beyond the resolution of previous squall line studies radar reflectivity filled in between cells at upper levels as the storm evolved reflectivity values were only weakly associated with updraft and downdraft magnitude the updrafts and downdrafts in the storm tended to be irregular in their three dimensional shape and less than 5 km in horizontal extent at any giv

the magnetic structure of axial seamount juan de fuca ridge axial seamount is a large volcanically active seamount located in the eastern pacific on the central juan de fuca jdf ridge at 46 n 130 w sea surface magnetic anomaly data show that axial lies completely within crust formed during the brunhes normal polarity epoch the edifice however does not produce a simple positive magnetic anomaly related to the excess mass above mean seafloor several pronounced negative magnetic anomalies are associated with the seamount including both a circular shaped low located west of the summit and an elongate low trending nw on the southeast flank of the volcano these two anomalies form part of a nw se magnetic trough which extends across the seamount edifice oblique to the general jdf ridge trend of n20 e a third negative anomaly is observed on the northern flank of the seamount associated with north helium basin a deep elongate basin which indents the northeast flank of the seamount both inversion of sea surface magnetics data and forward modelling of topography constrained by magnetization values of dredged samples show that bathymetric effects can explain the helium basin anomaly but topography alone cannot produce the low magnetization values which extend across the seamount summit magnetization of crustal rocks does not vary spatially over the seamount so that negative anomalies at the summit can be explained by variations in the effective thickness of the magnetic source layer a simple forward model of uniform magnetization shows that the anomaly source layer would have to thin by 50 to less than 700 m thick in order to generate the observed magnetic response a thinned source layer is consistent with the presence of either a substantial magma chamber at depth beneath the summit of axial or a zone of substantial crustal alteration the shape of the anomaly implies the trend of either of these sources must be oriented obliquely to the general ridge trend but parallel to the direction of the absolute plate motion

3 d inversions of magnetic gradiometer data in archeological prospecting possibilities and limitations a vertical gradient magnetic system based on optically pumped cesium sensors has been used to map subtle magnetic anomalies across infilled pit houses and ditches at a medieval archeological site in northern switzerland for estimating the locations and dimensions of these features from the recorded data we have designed and implemented an appropriate inversion scheme tests of this scheme on realistic synthetic data sets suggested that suitable minimum magnetic susceptibility contrasts and smoothing parameters for the inversion may be directly extracted from the data inversions with minimum magnetic susceptibility contrasts generated causative bodies with maximum plausible sizes by using higher magnetic susceptibility contrasts a complete suite of models that matched the data equally well was produced to constrain better the magnetic susceptibility constrast within a selected area of the archeological site shallow samples of topsoil and sediment were analyzed in the laboratory an inversion based o

the dynamics of the mississippi river plume impact of topography wind and offshore forcing on the fate of plume waters 1 high resolution numerical simulations of the northern gulf of mexico region using the hybrid coordinate ocean model hycom were employed to investigate the dynamical processes controlling the fate of the mississippi river plume in particular the conditions that favor cross marginal transport the study focuses on the effects of topography wind driven and eddy driven circulation on the offshore removal of plume waters a realistically forced simulation nested in a data assimilative regional gulf of mexico hycom model reveals that the offshore removal is a frequent plume pathway eastward wind driven currents promote large freshwater transport toward the shelf break and the desoto canyon where eddies with diameters ranging from 50 to 130 km interact with the buoyant plume and effectively entrain the riverine waters our estimates show that the offshore removal by eddies can be as large as the wind driven shelf transport the proximity of eddies to the shelf break is a sufficient condition for offshore removal and shelf to offshore interaction is facilitated by the steep bottom topography near the delta strong eddy plume interactions were observed when the loop current system impinged against the shelf break causing the formation of coherent narrow low salinity bands that extended toward the gulf interior the offshore pathways depend on the position of the eddies near the shelf edge their life span and the formation of eddy pairs that generate coherent cross shelf flows this study elucidates the dynamics that initiate a unique cross marginal removal mechanism of riverine low salinity nutrient rich waters allowing their export along connectivity pathways induced by a large scale current system

determining electric fields in thunderclouds with the radiotelescope lofar an analysis is presented of electric fields in thunderclouds using a recently proposed method based on measuring radio emission from extensive air shower events during thunderstorm conditions this method can be regarded as a tomography of thunderclouds using cosmic rays as probes the data cover the period from december 2011 till august 2014 we have developed an improved fitting procedure to be able to analyze the data our measurements show evidence for the main negative charge layer near the 10 isotherm this we have seen for a winter as well as for a summer cloud where multiple events pass through the same cloud and also the vertical component of the electric field could be reconstructed on the day of measurement of some cosmic ray events showing evidence for strong fields no lightning activity was detected within 100 km distance for the winter events the top heights were between 5 and 6 km while in the summer typical top heights of 9 km were seen large horizontal components in excess of 70 kv m of the electric fields are observed in the middle and top layers

crystal subdivisions of the eastern and central united states and a seismic boundary hypothesis for eastern seismicity potential field and surface geologic data may be used to subdivide the precambrian and phanerozoic crust of the eastern and central united states into several blocks these subdivisions are made by using the trends amplitudes and frequencies of magnetic anomalies in conjunction with gravity and surface geologic data most blocks appear unrelated to historical seismicity but between new mexico and georgia the edges of several blocks may be connected to form the northern boundary of a broad zone of very low earthquake activity we speculate that this southern zone has been decoupled from the stress regime affecting the remainder of the central and eastern united states and should experience few if any large earthquakes in the future as long as the present stress configuration is maintained

the relationship between lightning type and convective state of thunderclouds thunderstorm case studies and earlier observations are described which illuminate the relationship between cloud vertical development and the prevalence of intracloud ic and cloud to ground cg lightning a consistent temporal evolution starting with peak ic activity changing to predominant cg activity and concluding with strong outflow microburst suggests that ice is responsible for both the electrical i e lightning and dynamical i e microburst phenomena the ic activity is attributed to the updraft driven accumulation of graupel particles in the central dipole region and the subsequent cg activity to the descent of ice particles beneath the height of the main negative charge the subsequent descent and melting of ice particles beneath the height of the 0 c isotherm are associated with the acceleration of the downdraft and outflow the ic lightning precursor can provide a valuable short term 5 10 min warning for microburst hazard at ground level

electrical evolution during the decay stage of new mexico thunderstorms 1 the electric field e at the ground beneath a thunderstorm often exhibits an end of storm oscillation eoso during the storm s decay phase in which e typically undergoes three polarity changes over a period of 30 75 min to determine why the surface e oscillates the timing of the eoso polarity changes of a multicellular storm in new mexico has been compared to a series of balloon radar and lightning data three in situ balloon soundings provide vertical profiles of e and inferred charge regions just before and during the eoso these data have been compared to the evolving precipitation structure determined from orthogonal range height scans of two radars and to several other parameters including lightning mapping array data before the eoso began the storm had the typical electrical structure of the late mature stage estimates of the total charge magnitudes in each of the principal regions before and during the eoso ranged from 7 to 33 c the comparisons indicate that surface e polarity changes during the eoso were 1 primarily owing to the successive fallout of three of the four principal charge regions in the storm s mature stage charge structure modified by 2 the growth or decay of the charge regions as they descended and 3 changes in the screening charges at the upper and lower cloud boundaries more limited data from two other decaying storms indicate that similar in cloud evolution was probably occurring during their eosos

ballooning of river plume bulge and its stabilization by tidal currents when freshwater debouches into an adjacent ocean an anticyclonic eddy bulge is formed in front of the river mouth it is well known that a bulge growing offshore ballooning hardly reaches a steady state in the absence of either ambient currents or wind forcing this study provides a physical interpretation for the ballooning of river plume bulges by conducting numerical experiments in which a river plume is induced by a coastal freshwater source part of the freshwater released to the model ocean undergoes inertial instability near inertial oscillations are predominant when disturbances are not forced in ambient waters of the river plume these isotropic disturbances are amplified by inertial instability so that unstabilized freshwater can move in arbitrary directions thus unstabilized freshwater does not need to move toward the coastal boundary current on the right hand side of the river mouth freshwater unstabilized for a long time can stay in the bulge for a long time unstabilized freshwater accumulates gradually in the bulge and so ballooning occurs when the direction of disturbances is prescribed in ambient waters unstabilized freshwater is forced to move in the same direction thereby the motion of unstabilized freshwater is restricted in the alongshore direction when background disturbances are induced by alongshore tidal currents it is therefore concluded that tidal currents play a role in stabilizing the offshore growth of river plume bulges in coastal and shelf waters

relationships between lightning location and polarimetric radar signatures in a small mesoscale convective system abstract on 19 june 2004 the thunderstorm electrification and lightning experiment observed electrical microphysical and kinematic properties of a small mesoscale convective system mcs the primary observing systems were the oklahoma lightning mapping array the koun s band polarimetric radar two mobile c band doppler radars and balloonborne electric field meters during its mature phase this mcs had a normal tripolar charge structure lightning involved a midlevel negative charge between an upper and a lower positive charge and flash rates fluctuated between 80 and 100 flashes per minute most lightning was initiated within one of two altitude ranges 3 6 or 7 10 km msl and within the 35 dbz contours of convective cells embedded within the convective line the properties of two such cells were investigated in detail with the first lasting approximately 40 min and producing only 12 flashes and the second lasting over an hour and producing 105 flashes in both lightning was initiated in or nea

satellite synthetic aperture radar detection of delaware bay plumes jet like feature analysis current structure sech 2 h constitutes a determining factor for the radar image the modeled image intensity depends on the axial velocity decreasing as x 1 along the jet axis and is sensitive to the wind direction with respect to the jet axis the model was used to interpret synthetic aperture radar sar images of delaware bay plumes taken by the radarsat 1 canadian radar satellite and ers 2 european remote sensing satellite satellites during a period from summer 1996 to spring 1997 in all seasons the low salinity plumes appear as relatively bright jet like patterns on sar images from a morphological interpretation of the image features both summer and winter plumes can be divided into three sections along the axis source jet and dispersion region along the transverse direction sar image interpretations indicate that the plumes have a twin jet structure which conforms to decomposition of field measurements in summer the typical axial velocity is estimated at 6 10 1 ms 1 with a reynolds number of 18 at about 5 km downstream from the source the plume behaves like a turbulent jet and beyond that range down to about 10 km downstream it behaves like a laminar jet in winter the plumes become weaker than in summer the typical axial velocity is estimated at 4 10 1 ms 1 with a reynolds number of 3 the jet behaves like the laminar jet off the source down to about 4 km downstream in both summer and winter cases the sar images were taken at maximum flood tide and the plumes appeared as jets in the spring case the sar image was taken at early flood tide the plume appeared as an integrated body with relatively uniform bright tunes in all cases the plume disperses within about 25 km downstream index terms 4235 oceanography general estuarine processes 4528 oceanography physical fronts and jets 4546 oceanography physical nearshore processes 4568 oceanography physical turbulence diffusion and mixing processes keywords delaware bay estuarine plume radar image

dispersal of the pearl river plume over continental shelf in summer abstract satellite images of turbidity were used to study the climatological monthly and typical snapshot distributions of the pearl river plume over the shelf in summer from 2003 to 2016 these images show that the plume spreads offshore over the eastern shelf and is trapped near the coast over the western shelf eastward extension of the plume retreats from june to august monthly spatial variations of the plume are characterized by eastward spreading westward spreading or both time series of monthly plume area was quantified by applying the k mean clustering method to identify the turbid plume water decomposition of the 14 year monthly turbidity data by the empirical orthogonal function eof analysis isolated the 1st mode in both the eastward and westward spreading pattern as the time series closely related to the pearl river discharge and the 2nd mode with out of phase turbidity anomalies over the eastern and western shelves that is associated with the prevailing wind direction eight typical plume types were detected from the satellite snapshots they are characterized by coastal jet eastward offshore spreading westward spreading bidirectional spreading bulge isolated patch offshore branch and offshore filaments respectively their possible mechanisms are discussed

radar and lightning observations of normal and inverted polarity multicellular storms from steps abstract this study discusses radar and lightning observations of two multicellular storms observed during the severe thunderstorm electrification and precipitation study the lightning mapping array data indicated that the charge structure of the 19 june 2000 storm was consistent with a normal polarity tripole while the 22 june 2000 storm exhibited an overall inverted tripolar charge structure the 19 june storm consisted of weaker convection and produced little to no hail and moderate total flash rates peaking between 80 and 120 min 1 the cells in the 22 june 2000 storm were much more vigorous exhibited strong broad updrafts and produced large quantities of hail as well as extraordinary total flash rates as high as 500 min 1 the national lightning detection network nldn indicated that the 19 june storm produced mostly negative cloud to ground cg lightning while the 22 june storm produced predominantly positive cg lightning peaking at 10 min 1 just after two cells merged however the los al

the magnetic properties of metaperidotitic rocks as a function of metamorphic grade implications for crustal magnetic anomalies seventeen samples from the malenco serpentinite in the swiss alps representing systematic prograde metamorphic conditions from prehnite pumpellyite to upper amphibolite are moderately to strongly magnetic average susceptibility of 6 61 10 2 si units due predominantly to the presence of a magnetite rich spinel some greenschist facies samples contain the metal alloy awaruite ni3fe these contain in addition much greater amounts of magnetite small amounts of pyrrhotite in about half the samples complete the contributions to the total magnetization susceptibilities generally decrease with increasing metamorphic grade because of the production of increasing amounts of chromerich spinel which dilutes the magnetite component these results indicate that significant magnetic anomalies should be generated in suture zones containing metamorphosed serpentinite and in areas where serpentinite is being actively subducted

one dimensional time dependent modeling of gate cumulonimbus convection abstract a one dimensional time dependent cumulonimbus model is designed that unlike in previous one dimensional models simulates cloud top heights vertical velocities and water contents that are reasonably consistent with those observed in real convective cores the model successfully simulates deep tropical oceanic cumulonimbus with results that are in agreement with aircraft observations of vertical velocity observations of radar reflectivity and three dimensional model simulations these results are achieved by improving the parameterizations of the following physical processes vertical mixing through the inclusion of an overturning thermal circulation near cloud top lateral entrainment by modifying the assumed shape of the cloud initiating convection with sustained boundary layer forcing that resembles the lifting by gust fronts associated with tropical oceanic cumulonimbus and making the pressure perturbation internally consistent with the horizontal distribution of vertical velocity in th

evidence for a relationship between hydrocarbons and authigenic magnetite establishing a relationship between hydrocarbon migration and the precipitation of authigenic magnetite in sedimentary rocks is of significant interest with respect to 1 elucidating mechanisms for remagnetization and establishing the origin of secondary magnetizations residing in magnetite 2 developing a method to date hydrocarbon migration events by determining the time of remanence acquisition by palaeomagnetic methods and 3 evaluating whether searching for anomalous concentrations of diagenetic magnetic minerals and or aeromagnetic anomalies is justified as a relatively inexpensive exploration tool the direct association of hydrocarbon migration and the precipitation of authigenic magnetite has however not been established in this paper we report palaeomagnetic rock magnetic petrographic and geochemical results of a study of samples from permian spelebthems and gilsonite found in the ordovician arbuckle group in southern oklahoma the results indicate that there is a genetic relationship between hydrocarbon migration and the precipitation of authigenic magnetite

three dimensional numerical modeling of convection produced by interacting thunderstorm outflows part i control simulation and low level moisture variations abstract the klemp wilhelmson three dimensional numerical cloud model is used to investigate cloud development along intersecting thunderstorm outflow boundaries the model initial environment is characterized by a temperature and moisture profile typically found in strong convective situations and the initial wind field is prescribed by a constant unidirectional shear 2 9 m s 1 km 1 from 0 8 to 8 9 km with a constant wind everywhere else the wind shear vector is perpendicular to the line containing the two initial outflow producing clouds which are spaced 16 km apart and are triggered by thermal impulses centered at the top of the boundary layer the dynamics of the outflow collision are documented using time dependent kinematic air parcel trajectories and thermodynamic data we find that ambient air in the outflow collision region is literally squeezed out of the way as the two outflows collide some of this air is lifted to saturation triggering two convective clouds the upshear member of the

structure of an atmospheric undular bore generated from colliding boundaries during cape abstract a case study of a sea breeze front originating from the east coast of florida colliding with a gust front moving toward the southeast is presented single and multi doppler radar analyses combined with serial balloon ascents suggest that the denser sea breeze flow undercut the cold pool behind the gust front and may have generated a westward propagating undular bore in addition another undular bore was generated by the collision and propagated eastward through the cape network the latter bore propagated upstream against the southeasterly flow behind the sea breeze front and was apparent as a narrow band 5 6 km wide of near zero radial velocities embedded within an overall flow that was positive as seen by the cp 4 doppler radar as the eastern bore propagated through the dual doppler lobe defined by the ncar cp 3 and cp 4 radars a detailed and unique wind synthesis revealed its three dimensional kinematic structure significant along bore variability was shown in the convergence and verti

the dependence of numerically simulated convective storms on vertical wind shear and buoyancy abstract the effects of vertical wind shear and buoyancy on convective storm structure and evolution are investigated with the use of a three dimensional numerical cloud model by varying the magnitude of buoyant energy and one directional vertical shear over a wide range of environmental conditions associated with severe storms the model is able to produce a spectrum of storm types qualitatively similar to those observed in nature these include short lived single cells certain types of multicells and rotating supercells the relationship between wind shear and buoyancy is expressed in terms of a nondimensional convective parameter which delineates various regimes of storm structure and in particular suggests optimal conditions for the development of supercell type storms applications of this parameter to well documented severe storm cases agree favorably with the model results suggesting both the value of the model in studying these modes of convection as well as the value of this representation i

contributions of wood ash magnetism to archaeomagnetic properties of fire pits and hearths magnetic studies were conducted on a variety of plant ash and ash material from fire pits to investigate the possible contribution of ash to the magnetic signature of hearths the measurements included magnetic susceptibility remanence acquisition to saturation sirm alternating field demagnetization of sirm and remanent coercivity brc we conclude from these studies that wood ash produces fine grained magnetic iron oxides these oxides are probably magnetic that is concentrated enough to add to the magnetic signature of hearths and fire pits at one site ellicottville new york the ash layer exhibits a magnetic susceptibility that is 22 times greater than a control soil sample from the site we attribute this large enhancement to repeated burns at the site which continued to add ferromagnetic material to the fire pit the source of the magnetic material is probably phytoferritin from plants the variation in the intensity of magnetic anomalies over ancient hearths and fire pits may in part be caused by the magnetic contribution from ash

a model of ocean basin crustal magnetization appropriate for satellite elevation anomalies a model of ocean basin crustal magnetization measured at satellite altitudes is developed which will serve both as background to which anomalous magnetizations can be contrasted and as a beginning point for studies of tectonic modification of normal ocean crust the model is based on published data concerned with the petrology and magnetization of the ocean crust and consists of viscous magnetization and induced magnetization estimated for individual crustal layers thermal remanent magnetization and chemical remanent magnetization are excluded from the model because seafloor spreading anomalies are too short in wavelength to be resolved at satellite altitudes the exception to this generalization is found at the oceanic magnetic quiet zones where thermal remanent magnetization and chemical remanent magnetization must be considered along with viscous magnetization and induced magnetization

paleomagnetism of cretaceous pacific seamounts revisited the paleomagnetism of cretaceous pacific seamounts is reexamined herein techniques for nonuniform magnetic modeling are applied to determine paleomagnetic pole positions and their associated confidence limits modeling techniques are presented for reconstruction of both uniform and nonuniform components of the seamount magnetization the uniform component yields an estimate of the paleomagnetic pole position and the nonuniform component accounts for irregularities in the seamount magnetization a seminorm minimization approach constructs maximally uniform magnetizations and is used to represent seamount interiors a statistical modeling approach constructs random nonuniform magnetizations and is used to determine the confidence limits associated with each pole position mean paleopoles are calculated for groups of seamounts including their associated error bounds the mean paleopole for seven reliably dated upper cretaceous seamounts is located close to the position predicted by pacific hotspot relative motion the paleopole for five seamounts with cretaceous minimum dates is located west of the hotspotpredicted apparent polar wander path and may represent a lower cretaceous or upper jurassic pole

spatial patterns of convection in south florida abstract although they are a fairly consistent feature the sea breeze and lake breeze convergence lines and the associated convection over south florida during the summer may vary considerably from one day to the next daily radar maps indicate a few basic recurring patterns analyses of radiosonde data show significant differences corresponding to the different patterns in the local thermodynamic parameters most notably the mixing ratio changes in the synoptic scale wind field correspond closely to changes in the observed radar patterns and the local thermodynamic conditions explanation of the formation and development of the different patterns of convection is given in terms of the complex interaction between the regional synoptic peninsular and local scale circulations

archaeomagnetism and magnetic anomalies in the american southwest magnetic surveying is probably the most widely used geophysical technique at archaeological sites weymouth and huggins 1985 it is useful for locating features in which the magnetic susceptibility contrasts with the magnetic susceptibility of the surroundings because of induced and or remanent magnetization a contrast in magnetic induction can arise for example when the disturbed soil fill inside a formerly occupied room has a different magnetic susceptibility from the subsoil outside the room tite and mullins 1971 a contrast in magnetic remanence most commonly occurs when a baked clay artifact or feature such as a hearth has acquired a thermoremanent magnetization after being heated to several hundred degrees celsius

solar forcing induced spatial synchronisation of the east asian summer monsoon on centennial timescales abstract spatial patterns in centennial scale variations of the east asian summer monsoon easm during the holocene are poorly constrained due to the lack of high resolution records with detailed chronologies especially in southern china here we present high resolution 35 yr proxy records spanning the last 7500 years from a well dated sediment core yj core from the northern inner shelf of the south china sea al ti and fe variations were employed as indicators of terrigenous influx and k al ratios were used as a tracer of chemical weathering to document variations in the intensity of the easm the results show a series of centennial scale weak easm events which are generally synchronous with those inferred from other geologic archives from monsoonal regions in the eastern and southern china moreover these events are synchronous with periods of weak solar activity and the spectral analysis demonstrates that the easm and solar activity share some general cyclicity patterns we therefore suggest that solar activity is a fundamental driving force for the spatial synchronisation of the easm on centennial timescales across the monsoon region

meteorological and electrical conditions associated with positive cloud to ground lightning abstract meteorological and electrical conditions associated with the occurrence of positive cloud to ground cg lightning i e lightning that lowers positive charge to ground are examined results from case studies in winter and summer storms reveal common features and lend support to the tilted dipole hypothesis lightning bipoles whose lengths range from the convective scale to the mesoscale are aligned with the vertical wind shear with a predominance of negative locations in proximity to the deepest convection and a mixture of positive and negative locations displaced downshear from the deepest convection comparisons with radar data show that all lightning events am located within a distance of 10 20 km of precipitation extending from the surface to several kilometers above the o c isotherm electrostatic field measurements beneath precipitation removed from the deepest convection indicate a positive dipole structure and a tilting deformation by vertical wind shear these observations suggest

evidence for a shallow pluton beneath the goat rocks wilderness washington from gravity and magnetic data a gravity and aeromagnetic study was conducted in and adjacent to the goat rocks wilderness area washington this work was done in conjunction with geologic and geochemical studies which were critically important to our interpretation the bouguer gravity anomaly map displays a large central positive gravity anomaly and three superimposed smaller positive anomalies the main anomaly about 26 by 11 km with an amplitude of about 16 mgal seems to delineate a dense large pluton or sheeted dike complex intruding less dense older volcanic and sedimentary rocks lying directly below the volcano the pluton or sheeted dike complex may have fed the goat rocks volcano throughout its 1 2 m y history three small feeders mapped on the surface as andesite intrusions may be the cause of three smaller gravity anomalies superimposed on the main anomaly the magnetic anomaly maps also exhibit a large central anomaly whose source is the goat rocks pluton the magnetic data suggest that the three shallow intrusive cupolas have undergone a significant amount of hydrothermal alteration in addition to some extent the magnetic data reflect the terrain of the area topographic highs produce magnetic highs and topographic lows produce magnetic lows the deviations from this pattern delineate subsurface geology magnetic lows may be of particular interest in locating zones of mineralization where magnetic minerals have been altered and have become significantly less magnetic

tidal modulation on the changjiang river plume in summer 1 tide effects on the structure of the near field changjiang river plume and on the extension of the far field plume have often been neglected in analysis and numerical simulations which is the focus of this study numerical experiments highlighted the crucial role of the tidal forcing in modulating the changjiang river plume without the tidal forcing the plume results in an unrealistic upstream extension along the jiangsu coast with the tidal forcing the vertical mixing increases resulting in a strong horizontal salinity gradient at the northern side of the changjiang river mouth along the jiangsu coast which acts as a dynamic barrier and restricts the northward migration of the plume furthermore the tidal forcing produces a bidirectional plume structure in the near field and the plume separation is located at the head of the submarine canyon a significant bulge occurs around the head of the submarine canyon and rotates anticyclonically which carries a large portion of the diluted water toward the northeast and merges into the far field plume a portion of the diluted water moves toward the southeast which is mainly caused by tidal rectification this bidirectional plume structure is more evident under certain wind conditions during the neap tide with the reduced tidal energy the near field plume extends farther offshore and the bulge becomes less evident these dynamic behaviors are maintained and are fundamentally important in the region around the river mouth even under the summer monsoon and the shelf currents although in the far field the wind forcing and shelf currents eventually dominate the plume extension

development of upwelling on pathway and freshwater transport of pearl river plume in northeastern south china sea in situ observations satellite images and numerical modeling results have shown that the pearl river plume axis extends alongshore and passes through two separate upwelling regions one off the guangdong and fujian coasts the yuedong upwelling and the other in the taiwan bank during the initial and medium stages of the yuedong upwelling while it is directed offshore when the yuedong upwelling is fully developed model experiments are conducted to examine the effects of wind strength and baroclinicity on the upwelling and the corresponding pathway and freshwater transport of the pearl river plume the baroclinic effect is important to intensifying the horizontal velocity at the upwelling front and freshwater transport in the northeastern south china sea the freshwater transport flux is further decomposed into advection vertical shear and tidal pumping components and advection is the dominant contributor as the yuedong upwelling develops the zone with a relatively high pressure gradient moves offshore due to offshore ekman transport and the shift in the upwelling front which is responsible for the offshore transport of the river plume when the river plume is transported to the outer shelf sometimes it can be further entrained into eddies allowing its export to the open sea

crustal structure interpreted from magnetic anomalies this review discusses publications during the last quadrennium 1987 1990 that used aeromagnetic data marine magnetic data satellite magnetic data and rock magnetic and petrologic data to provide information on the sources of magnetic anomalies the publications reviewed reflect increased integration of rock magnetic property and petrologic studies with magnetic anomaly interpretation studies particularly in deep crustal magnetization exploration for hydrocarbons and inversion of marine magnetic anomalies interpretations of aeromagnetic data featuring image display techniques and using the horizontal gradient method for locating magnetization boundaries became standard

paleogene history of the kula plate offshore evidence and onshore implications paleocene to middle eocene magnetic anomalies were mapped over oceanic crust that accreted at the kula pacific spreading center and is now obliquely entering the western aleutian trench between 179 e and 168 e the strike of anomalies and the pattern of abyssal hills and fracture zones changed abruptly during 56 55 ma when north south spreading veered to northwest southeast 310 130 kula pacific spreading ceased in 43 ma a 75 km long section of the fossil kula rift axis has avoided subduction although it now intersects the trench axis almost orthogonally near 171 5 e a narrow remnant of the former kula plate northwest of this fossil spreading center is bounded by a fossil kula pacific transform with a high transverse ridge alongside a sediment filled transform valley anomalies on this remnant show that eocene kula pacific spreading was highly asymmetric 2 1 the 56 55 ma change in kula plate rotation inferred from the change in spreading direction coincided with birth of the aleutian subduction zone and was probably a consequence of the resulting change in slab pull stresses on the oceanic lithosphere the change in direction of kula north american motion is a plausible explanation for the detachment of continental terranes from the pacific northwest and their migration around the gulf of alaska and for the early eocene demise of alaska range are volcanism the cessation of kula pacific spreading coincides with a major change in pacific plate rotation and the subsequent direction of convergence of the pacific plate with the aleutian arc was similar to the 55 43 ma direction of kula plate convergence

deep convective cloud top heights and their thermodynamic control during crystal face 1 infrared 11 m radiances from goes 8 and local radiosonde profiles collected during the cirrus regional study of tropical anvils and cirrus layers florida area cirrus experiment crystal face in july 2002 are used to assess the vertical distribution of florida area deep convective cloud top height and test predictions as to its variation based on parcel theory the highest infrared tops z11 reached approximately to the cold point at 15 4 km though these are uncertain by about 1 km due to unknown cloud environment temperature differences since lidar shows that visible tops are generally 1 km or more above z11 visible cloud tops frequently penetrated the lapse rate tropopause 15 km further since tropospheric ice concentrations were typically present up to 1 km above the visible tops lofting of moisture through the mean cold point was probably common morning clouds and those near key west rarely penetrated the tropopause as in previous studies nonentraining parcel theory fails to explain either of these results though it does show promise in explaining day to day variations over the peninsula moisture variations above the boundary layer account for much of the day to day z11 variability especially over the oceans in all locations a 20 increase in mean mixing ratio between 750 and 500 hpa was associated with about 1 km deeper maximum cloud penetration other things being equal this sensitivity is too large to explain by simple dilution of parcel buoyancy through mixing implying microphysical or dynamical feedbacks on cloud development the evident influence of midtropospheric humidity on the depth of the tropical troposphere suggests an interesting climate feedback possibility for stabilizing midtropospheric relative humidity

a tidally dependent plume bulge at the pearl river estuary mouth abstract both observations and numerical simulations have proven the existence of a plume bulge at the trumpet like pearl river estuary pre the formation dynamic of the pre plume bulge during the southeasterly wind period is investigated with numerical model simulations based on the regional ocean modelling system roms the results indicate that the formation and evolution of the pre plume bulge is strongly modulated by the tidal cycle the bulge is sustained by the strong jet flow along the longitudinal lantau channel which is induced by the ebb current and transports freshwater offshore its size is significantly modulated by spring neap cycle being large during spring tide and very small during neap tide besides the existence of abundant freshwater in the estuary is a precondition for the formation of bulge the ebb jet flow could be strengthened by lateral buoyancy forcing which is induced by the accumulated freshwater in the estuary thus guarantees the offshore extension of bulge the input momentum flux by the river runoff however makes no significant contribution the work indicates a new mechanism of plume bulge formation at a wide estuary and evaluates the impact of different forcings

electrical and multiparameter radar observations of a severe hailstorm using data from the 11 cm csu chill multiparameter radar the simultaneous evolution of the radar inferred precipitation structure and electrical characteristics of a severe hailstorm is investigated we compare the substorm point discharge current intracloud ic lightning flash rate cloud to ground cg lightning flash rate ground strike location and flash polarity to the progression of precipitation types and amounts this study is unique in that it presents multiparameter radar observations of a thunderstorm complex which exhibited an extremely high ic to cg ratio ic cg 20 70 and predominantly positive cg lightning over 74 after it became severe producing large hail and weak tornadoes in particular we investigate the reported relationship between large hail and positive cg lightning although a direct correlation is found between a rapid increase in ic cg the first positive cg lightning flashes and the initial production of hail aloft the temporal and spatial behavior of large hail and positive cg lightning appear to be anticorrelated as broad peaks in the positive cg flash rate lag relative maxima in the fallout of large hail by up to 30 min the majority of positive ground strikes were adjacent to the main precipitation core in a region of light rain and little or no hail at the surface aloft radar data indicated that ice crystals were aligned vertically in a strong electric field corona point observations at the surface indicate that these regions adjacent to the convective core were characterized by net positive charge aloft possible mechanisms to explain these observations are discussed

an aeromagnetic study of mount st helens aeromagnetic data from surveys flown by the u s geological survey over mount st helens washington before and after the climactic may 18 1980 eruption were used to determine the bulk magnetic properties of the volcano and to delineate a buried source we assumed that most of the edifice of preeruption and posteruption mount st helens has a magnetization direction near the present earth s field of 69 inclination and 20 declination and calculated its intensity as 4 1 a m after subtraction of magnetic anomalies due to topogaphy magnetized with this direction and intensity the preeruption and posteruption surveys revealed nearly identical residual magnetic highs and lows indicative that their sources were not altered or removed by the may 1980 eruption the residual highs were explained by a 200 m deep source lying mostly within the edifice of mount st helens the source could be terrain that predates mount st helens such as a buried ridge or a cone or a valley filled with lava we calculated the magnetization of the material removed by the may 1980 eruption and found its intensity to be 4 2 a m in a direction near the present earth s field similar to that assumed for the volcano as a whole this similar result confirmed the validity of the magnetization vector assumed for the entire edifice

somali basin chain ridge and origin of the northern somali basin gravity and geoid low the northern somali basin located between chain ridge and the horn of africa north of 4 n is characterized by a distinct 5 m geoid low and by large negative gravity anomalies the boundaries of the basin are marked by steep gradients in both gravity and geoid basement in northern somali basin is 1 2 km deeper than on the carlsberg ridge flank to the southeast or on the sheba ridge flank to the north with a sharp discontinuity across the boundary of the basin the western somali basin to the south was created in the late jurassic and early cretaceous by the movement of madagascar away from africa reinterpretation of the magnetic anomalies in the western somali basin shows that they record both limbs of a mid ocean ridge that was active by m22 time kimmeridgian and died soon after mo aptian magnetic and gravity data allow the relict ridge crest to be traced from davie ridge near the african coast to the dhow vlcc ars fracture zone complex at 50 e davie ridge is a transform fault connecting the western somali basin spreading center with a similar age spreading center in the mozambique basin the dhow vlcc ars complex can be shown to continue north of the 4 n bathymetric high separating the northern and western somali basins and to intersect the african margin near 7 n the northern somali basin thus appears to be the third of a series of oceanic basins separated by long transform faults created during movement between east and west gondwanaland the original northern somali basin was split apart by the northward motion of india in the late cretaceous and chain ridge formed along the new boundary thermal and gravity modeling shows that the flexure resulting from differential subsidence across chain ridge combined with the difference in lithospheric thermal structure late jurassic vs early tertiary on either side of it explains well the amplitude and shape of the observed geoid step and gravity anomalies across chain ridge the geoid step up from the basin up to the african coast can be modeled as an edge effect between the juxtaposed jurassic oceanic and african continental crust thus the geoid and gravity low over the northern somali basin results from the superposition of a continental edge effect anomaly and the fracture zone edge effect anomaly

crustal magnetization in the south atlantic from inversion of magnetic anomalies a method for inverting magnetic anomalies in the presence of topography parker and huestis 1974 is used to analyze and describe crustal magnetization along 12 profiles in the south atlantic the profiles are approximately 2000 km long and are almost perpendicular to the trend of the magnetic anomalies a bandpass filter is used to remove long wavelength anomalies unassociated with seafloor spreading processes a filter that passes only wavelengths between 200 and 3 km produces a magnetization that approximates the positive and negative aspects of the geomagnetic reversal sequence the positive aspects originating from normally magnetized portions of the crustal source and negative aspects originating from reversely magnetized portions of the crustal source a 6 km thick crust is assumed in order to produce magnetizations consistent with dredged oceanic rocks a long wavelength pattern is evident in the magnetization solutions the highest magnetizations are associated with the ridge crest 1 35 1 74 a m within the western section of the study area a sharp decrease in magnetization occurs within 100 km of the ridge crest 4 5 ma a minimum in magnetization is reached at 400 km from the axis or at 18 ma 0 51 0 57 a m the magnetization then gradually increases out to 1100 km from the ridge axis or 50 ma 0 91 0 93 a m and dramatically decreases to 1900 km or 86 ma 0 34 0 43 a m within the eastern section of the study area a sharp decrease in magnetization occurs within the first 100 km of the ridge crest 5 ma a minimum in the magnetization occurs at approximately 400 km from the ridge axis or at 20 ma 0 54 0 56 a m the magnetization then gradually increases out to 1200 km from the ridge axis or to 60 ma 1 15 1 24 a m an overall pronounced decrease occurs to 1900 km from the ridge axis or to 95 ma 0 36 0 40 a m in order to explain this behavior the field intensity may have changed with a time scale of several millions of years alternatively the higher magnetizations at 50 60 ma could be explained by a uniform intensity of magnetization in a thicker crust

structure and eastward extension of the changjiang river plume in the east china sea 1 the hydrographic structure and offshore extension of freshwater plume discharged from the changjiang also known as the yangtze river in the northern east china sea were investigated by analyzing conductivity temperature depth ctd data and drifter trajectories collected during the summers of 1997 and 1998 from june to early september when southerly winds prevail the plume tends to move northeast in the chinese coastal area and then separates from the coastal zone to travel eastward over 400 km offshore across the western shelf of the northern east china sea during other seasons when northerly winds prevail the plume is confined to the chinese coast in the summer the plume in the midshelf confined to a thin surface layer 10 to 15 m thick extends eastward in the form of patches of low salinity water rather than spreading as a tongue shaped pattern from the changjiang mouth the eastward movement of patches in the western shelf is primarily due to upwelling favorable southerly winds upon reaching the vicinity of cheju do an island in the middle of northern east china sea the patches are advected to the korea tsushima strait by either the cheju warm current or a northward flowing mean current of the kuroshio branch current and then finally flow into the east japan sea

the relationship between precipitation and lightning in tropical island convection a c band polarimetric radar study one of the primary scientific objectives of the maritime continent thunderstorm experiment was to study cloud electrification processes in tropical island convection in particular the coupling between ice phase precipitation and lightning production to accomplish this goal a c band polarimetric radar was deployed in the tropics 11 68s 130 88e for the first time accompanied by a suite of lightning measurements using observations of the propagation corrected horizontal reflectivity and differential reflectivity along with specific differential phase rain and ice masses were estimated during the entire life cycle of an electrically active tropical convective complex known locally as hector over the tiwi islands on 28 november 1995 hector s precipitation structure as inferred from these raw and derived radar fields was then compared in time and space to the measured surface electric field cloud to ground cg and total lightning flash rates and ground strike locations during hector s developing stage precipitating convective cells along island sea breezes were dominated by warm rain processes no significant electric fields or lightning were associated with this stage of hector despite substantial rainfall rates aided by gust front forcing a cumulus merger process resulted in larger taller and more intense convective complexes that were dominated by mixed phase precipitation processes during the mature phase of hector lightning and the surface electric field were strongly correlated to the mixed phase ice mass and rainfall merged convective complexes produced 97 of the rainfall and mixed phase ice mass and 100 of the cg lightning as hector dissipated lightning activity rapidly ceased as evidenced from the multiparameter radar observations the multicell nature of hector resulted in the continuous lofting of supercooled drops to temperatures between 2108 and 2208c in discrete updraft cores during both the early and mature phases the freezing of these drops provided instantaneous precipitation sized ice particles that may have subsequently rimed and participated in thunderstorm electrification via the noninductive charging mechanism

crustal evolution and the granulite to eclogite transition in xenoliths from kimberlites in the west african craton a petrographic mineral and bulk chemical study of a xenolith suite of granulites and eclogites from sample creek liberia and koidu sierra leone has been undertaken with a view to determining the nature of the crust upper mantle interface a broad range of xenolith compositions is present from high mgo eclogites to garnet anorthosites and a systematic afm trend is established consistent with mafic and ultramafic melt fractionation at moderate pressures 10 20 kbar a trend is established for the entire xenolith suite among bulk chemistry seismic p wave velocity and a crust mantle c m bulk chemical ratio defined as na2o k2o sio2 feo mgo mole three populations are present a granulitic crustal group sg 3 0 a granulite and eclogite transitional group sg 3 0 3 3 vp 7 2 8 0 km s c m 1 5 3 0 andanexclusivelyuppermantleeclogiticgroup ifsg 3 3 vp 8 2 8 7 km s c m 1 5 from these data and coupled with garnet clinopyroxene mineral thermometry and accessory phases e g diamond graphite coesite kyanite or the presence of plagioclase a xenolith geotherm is established based on stratigraphic sequencing and phase transition boundaries diamond and coesite bearing eclogites conform to the 40 mw m2 standard cratonic low heat flow geotherm whereas the plagioclase granulites at lower pressures correspond to an average rift geotherm of 90 mw m2 the latter is ascribed to igneous underplating onto the lower crust or to thermal perturbations from an earlier tectonic event graphite and kyanite eclogites and the transitional group in sg vp and c m ratio of eclogites and granulites fall between the 40 and 90 mw m2 reference geotherms the xenoliths are meta igneous the lower crust and uppermost mantle are mafic in composition and the petrologic moho is an intercalated interstratified horizon of eclogite and garnet granulite growth of the early crust was largely a consequence of asthenospheric depletion in which underplating rather than lateral accretion was dominant

the columbia river plume study subtidal variability in the velocity and salinity fields a comprehensive study of the strongly wind driven midlatitude buoyant plume from the columbia river located on the u s west coast demonstrates that the plume has two basic structures during the fall winter season namely a thin 5 15 m strongly stratified plume tending west to northwestward during periods of southward or light northward wind stress and a thicker 10 40 m weakly stratified plume tending northward and hugging the coast during periods of stronger northward stress the plume and its velocity field respond nearly instantaneously to changes in wind speed or direction and the wind fluctuations have timescales of 2 10 days frictional wind driven currents cause the primarily unidirectional flow down the plume axis to veer to the right or left of the axis for northward or southward winds respectively farther downstream currents turn to parallel rather than cross salinity contours consistent with a geostrophic balance in particular during periods when the plume is separated from the coast currents tend to flow around the mound of fresher water at distances exceeding about 20 km from the river mouth the along shelf depth averaged flow over the inner to midshelf is linear and depth averaged acceleration is governed to lowest order by the difference between surface and bottom stress alone in this region along shelf geostrophic buoyancy driven currents at 5 m calculated from surface density and along shelf geostrophic wind driven currents computed from a depth averaged linear model are comparable in magnitude 10 25 cm s 1

doppler radar signatures of developing thunderstorms and their potential to indicate the onset of cloud to ground lightning abstract the capability of doppler weather radars to short term forecast the initiation of thunderstorms and the onset of cloud to ground cg lightning is examined doppler weather radar data from 28 thunderstorms were analyzed from august 1990 in the central florida environment these radar echoes were associated with cg lightning strike locations from the national lightning detection network and two lightning detection systems operated by the u s air force in the vicinity of kennedy space center from a time history of these radar echoes it was found that a 10 dbz echo first detected near the freezing level may be the first definitive echo of a future thunderstorm this thunderstorm initiation signature is often accompanied by low altitude convergence and divergence at the top of the radar echo the observed lead times between this thunderstorm initiation signature and the first detected cg lightning strike ranged from 5 to 45 min with a median lead time of 15 min all lightning producing radar echo

thunderstorm initiation organization and lifetime associated with florida boundary layer convergence lines abstract the initiation organization and longevity of thunderstorms associated with boundary layer convergence lines in the cape canaveral florida vicinity are examined using data from the convection and precipitation electrification cape experiment the project was conducted during july and august 1991 under low vertical wind shear situations this observational study is based on doppler radar mesonet balloon sounding and satellite data the primary convergence lines studied were the east coast sea breeze front ecsbf and a frequently occurring gust front from the west termed the west coast front wcf that originates with storms initiated by the west coast sea breeze front significantly fewer storms were associated with the ecsbf in comparison to the wcf this was because the convergence with the ecsbf was shallower and weaker and the updrafts were shallow and tilted the environmental winds were generally westerly near the top of the ecsbf and at storm steering level as a result the low le

tectonic evolution of the northern pacific plate and pacific farallon izanagi triple junction in the late jurassic and early cretaceous m21 m10 abstract magnetic lineations in the northwestern pacific near the shatsky plateau were interpreted to trace the tectonic history of the northern pacific plate from the time of anomalies m21 to m10 at m22 time the pacific farallon izanagi p f i triple junction was located southwest of the plateau and migrating north northwest with respect to the pacific plate shortly thereafter the stress field acting on the three plates changed significantly and the pacific lzanagi ridge reacted by pivoting 24 clockwise from m21 to m19 time several ridge propagation events occurred while the ridge adjusted to the new spreading regime to the east of the m22 location of the junction it appears that this reorganization triggered a series of at least three ridge jumps along the pacific farallon ridge the geometry of magnetic isochron m21 suggests that several triple junctions existed simultaneously during the reorganization bordering one or more microplates differences in the spreading rate of the japanese magnetic lineations north of the plateau imply that one microplate which we call the shatsky microplate existed until about m15 m13 time it was probably captured by either the farallon or the izanagi plate and subsequently destroyed by subduction after m15 the p f i triple junction was reformed on seafloor that is now beneath the shatsky plateau the junction drifted generally northeast either in a ridge ridge ridge or in a ridge fault fault configuration perhaps alternating between the two from m11 m10 time the stress field on the three plates changed again and the pacific farallon ridge southeast of the plateau reoriented 15 clockwise at this time the p f i junction assumed a ridge ridge ridge geometry at the northeast end of the plateau

observations and numerical modeling of the pearl river plume in summer season a cruise survey of the pearl river plume during southeasterly and southwesterly winds two typical wind patterns in summer in guangdong coastal waters is reported and the cruise data are analyzed to unveil the plume dynamics the kelvin number is derived from the in situ data revealing that the pearl river plume exhibits two different scales in response to the two kinds of the wind forcing numerical model simulations based on the regional oceanic modeling system roms with nesting domains are implemented to explore details of the plume dynamics validated by cruise observations and tidal gauge sea level data modeling results suggest that there is a subtidal anticyclonic recirculation bulge on the west side out of the estuary mouth under southeasterly winds showing a recirculating plume in the near field when the wind changes to the southwesterly however the recirculating plume vanishes the distinct supercritical tidal plume front occurs with southeasterly winds prevailing in spring tide due to the strong advection in the tidal plume the tidal salt deficit flux can reach as high as 12 5 of the mean current flux and illustrates the combined forcing of tide and wind key points the paper clarifies the pearl river plume anatomy under two typical winds spring tide facilitates the supercritical pearl river tidal plume front tide determines tidal salt deficit flux strength wind determines the direction

the diurnal interaction between convection and peninsular scale forcing over south florida abstract surface wind measurements taken during the summers of 1973 and 1975 in the florida area cumulus experiments face fine mesh networks are used to calculate surface divergence on the convective scale and mesoscale examination of the daily time series of divergence averaged over a 30 km 25 km grid showed that on days with deep convective activity over and around the network a definable sequence in the network averaged surface wind divergence is observed the sequence consists of five stages persistent convergence peak convergence non divergence peak divergence and the return to a non divergent state use is made of observations of individual cases and of radar composites built around the above sequence in the network averaged divergence fields to demonstrate that a convective scale feedback mechanism consisting of outflows from previous storms triggering new growth is frequently observed during both experimental periods it is shown that the observations taken over the face 1975 network are

thunderstorm electrification a case study the paper presents interpretation of triple doppler radar observations of a thunderstorm that occurred at the kennedy space center florida precipitation particle motions inside the storm as evaluated from the three radial velocity radar data sets are presented in a selected vertical plane throughout the storm development these data are interpreted and compared with observations of vhf radio emission sources and lightning charge centers derived from an earlier analysis krehbiel 1981 the main feature of the particle motion field is the persistence at nearly the same altitude throughout the entire period of analysis of a balance level characterized by a zero value of the precipitation particle mean vertical velocity further analysis based on considerations of radar reflectivity and air velocity suggests the presence at this altitude of relatively large precipitation particles suspended in an updraft the lightning negative charge centers appear to be less than 1 km above the particle balance level

mesoscale eddies in the northwestern subtropical pacific ocean statistical characteristics and three dimensional structures mesoscale eddy properties in the northwestern subtropical pacific ocean are investigated by analyzing 22 567 cyclonic eddies ces and 26 365 anticyclonic eddies aes detected from 19 year altimetric sea level records eddy occurrence frequency and kinetic energy are prevailingly high in the subtropical countercurrent zonal band between 19 degrees n and 26 degrees n and further elevated near the luzon taiwan coast a general superiority of aes is observed at most latitudes except between 19 degrees n and 22 degrees n where the ce number is larger the modal radius and mean lifespan of the ces aes are 134km and 11 2weeks 121km and 10 9weeks respectively after generation most eddies propagate westward with a mean speed of 7 2cms 1 and deflect northward following the kuroshio along the luzon taiwan coast three dimensional eddy structures are further explored with composite eddy images in five subregions constructed by surfacing argo temperature salinity data into altimeter detected eddy areas due to the existence of mode waters in the main thermocline eddy induced temperature anomaly exhibits a double core vertical structure which is especially evident in ce images because of the vertical water mass distribution salinity anomaly features a sandwich like pattern which is more evident in ae images also revealed is the significant structure difference in these five subregions eddies are greatly intensified as they approach the western boundary inducing larger temperature and salinity anomalies and influencing deeper ocean along the luzon taiwan coast aes are preferentially strengthened by the northward background flow

electrical and polarimetric radar observations of a multicell storm in telex abstract on 28 29 june 2004 a multicellular thunderstorm west of oklahoma city oklahoma was probed as part of the thunderstorm electrification and lightning experiment field program this study makes use of radar observations from the norman oklahoma polarimetric weather surveillance radar 1988 doppler three dimensional lightning mapping data from the oklahoma lightning mapping array lma and balloon borne vector electric field meter efm measurements the storm had a low flash rate 30 flashes in 40 min four charge regions were inferred from a combination of lma and efm data lower positive charge near 4 km and midlevel negative charge from 4 5 to 6 km msl from 0 to 6 5 c were generated in and adjacent to a vigorous updraft pulse further midlevel negative charge from 4 5 to 6 km msl and upper positive charge from 6 to 8 km from 6 5 to 19 c were generated later in quantity sufficient to initiate lightning as the updraft decayed a negative screening layer was present near the storm top

rainfall morphology in florida convergence zones a numerical study abstract central florida is the ideal test laboratory for studying convergence zone induced convection the region regularly experiences sea breeze fronts and rainfall induced outflow boundaries the focus of this study is convection associated with the commonly occurring convergence zone established by the interaction of the sea breeze front and an outflow boundary previous studies have investigated mechanisms primarily affecting storm initiation by such convergence zones few have focused on rainfall morphology yet these storms contribute a significant amount of precipitation to the annual rainfall budget low level convergence and midtropospheric moisture have been shown to be correlated with rainfall amounts in florida using 2d and 3d numerical simulations the roles of low level convergence and midtropospheric moisture in rainfall evolution are examined the results indicate that area and time averaged vertical moisture flux vmf at the sea breeze front outflow convergence zone is directly and

a revised estimate of pacific north america motion and implications for western north america plate boundary zone tectonics for the past 20 years much effort has been directed to determining the present day relative motion of the pacific and north american plates using two independent approaches one uses geologic observations and geodetic measurements along the san andreas fault and other faults in the plate boundary zone the other is based on plate motion models that incorporate spreading rates from marine magnetic anomalies transform azimuths and earthquake slip vectors geologic and geodetic studies find two principal elements of deformation slip along the san andreas of 34 mm yr directed n41 w and extension across the basin and range province of about 10 mm yr directed n56 w in contrast plate motion studies find 56 60 mm yr directed n35 w the discrepancy between these estimates a vector of about 15 mm yr oriented nearly due north is often attributed to a combination of slip along faults parallel to the san andreas and shortening normal to it here we revise the estimate of pacific north america motion by analyzing marine magnetic profiles from the gulf of california since 3 ma spreading has averaged 48 mm yr 10 mm yr slower than estimated before and consistent with the 49 mm yr spreading predicted by a new global plate motion model derived without any data along the pacific north america boundary the discrepancy with geodetic and geologic estimates is thus reduced to only 5 mm yr parallel to the san andreas 60 less than estimated before and 7 mm yr of shortening across the san andreas similar to prior estimates these results suggest that strike slip motion on faults west of the san andreas is less than thought before a conclusion consistent with geodetic seismological and other geologic observations

a numerical study of coupled estuary shelf circulation around the pearl river estuary during summer responses to variable winds tides and river discharge abstract the mean sub tidal circulations in the pearl river estuary pre and over the adjacent shelf are interactive they are driven by multi forcing of winds tides and the buoyancy of river discharge utilizing a validated three dimensional high resolution numerical model we find that the circulation in the pre during summer is dominated by an advective gravitational two layer circulation in the upper estuary and the landward part of the lower pre where the surface flow pattern also varies with the upwelling winds the circulation in the seaward part of the lower pre is governed by both gravitational circulation and geostrophic intrusive current from the shelf the pattern and intensity of these circulations are largely modulated by variable wind forcing the cross shore upwelling shelf circulation off the pre enhances the water exchange rate between the shelf and the pre but the net intrusive transport into the pre is negatively correlated with the intensity of upwelling favorable wind stress relatively strong water exchange rate between the shelf and estuary occurs during upwelling which reduces the flushing time of the estuary although the ebbing flooding tide strengthens weakens the eastward alongshore upwelling current tidal effect on the upwelling circulation and on the net transport between the shelf and estuary is not significant over the sub tidal period the shelf influences the estuary mainly through the intrusions of the shelf waters at the western bank and along the two navigation channels of the pre and they are governed by geostrophic cross shelf upwelling circulation and by gravitational intrusive currents due to pressure gradients yielded by the alongshore variation of the upwelling shelf circulation and by the buoyancy forcing of the river plume respectively

a two dimensional numerical investigation of the interaction between sea breezes and deep convection over the florida peninsula abstract deep convection initiated by sea breezes over the florida peninsula is simulated using a two dimensional nonhydrostatic model reasonable agreement is obtained between model results and observations for the three types of undisturbed days classified by blanchard and lopez the convergence of the east and west coast sea breezes is the primary control on the timing and location of rapid convective development and this is mainly determined by the low level winds the simulated convection is spatially concentrated and does not produce an extensive stratiform region sensitivity tests are performed for a variety of wind and thermodynamic profiles and for different soil moisture contents during the early stages of these simulations small convective cells develop in between the sea breeze fronts as the outer cells at the sea breeze fronts deepen these smaller cells are suppressed typically during the midafternoon a new cell explosively develops in between the sea breeze fronts and the outer cells

a comprehensive habit diagram for atmospheric ice crystals confirmation from the laboratory airs ii and other field studies abstract recent laboratory experiments and in situ observations have produced results in broad agreement with respect to ice crystal habits in the atmosphere these studies reveal that the ice crystal habit at 20 c is platelike extending to 40 c and not columnar as indicated in many habit diagrams found in atmospheric science journals and texts these diagrams were typically derived decades ago from laboratory studies some with inherent habit bias or from combinations of laboratory and in situ observations at the ground observations that often did not account for habit modification by precipitation from overlying clouds of varying temperatures habit predictions from these diagrams often disagreed with in situ observations at temperatures below 20 c more recent laboratory and in situ studies have achieved a consensus on atmospheric ice crystal habits that differs from the traditional habit diagrams these newer results can now be combined to give a comprehensive description of ice crystal habits

a numerical case study of convection initiation along colliding convergence boundaries in northeast colorado abstract a numerical cloud model has been used to simulate convective storm development on 17 july 1987 in northeast colorado the study involves the simulation of convergence along atmospheric boundaries and the subsequent development of convection the model was initialized using observed conditions for this case day from the convection initiation and downburst experiment cinde a two dimensional version of the clark ncar nested grid model is employed results indicate that convection in boundary line collision cases can be successfully simulated by using actual observed atmospheric data gradual deepening of the moisture layer in the convergence zone was shown to destabilize the local atmosphere leading to the initiation of deep convection on this day the modeled storm approximated the depth and intensity of the observed storms and displayed many of the features of the actual event sensitivity studies revealed that the timing and intensity of convection along boundaries is greatly affected by alter

electrification life cycle of incipient thunderstorms this work evaluates how clouds evolve to thunderstorms in terms of microphysical characteristics and produces the first intracloud ic and cloud to ground cg lightning flashes observations of 46 compact isolated thunderstorms during the 2011 2012 spring summer in southeast brazil with the x band polarimetric radar and two and three dimensional lightning location systems demonstrated key parameters in a cloud s vertical structure that produce the initial electrification and lightning activity the majority 98 of the first cg flashes were preceded by approximately 6 min by intracloud ic lightning the most important aspect of the observations going into this paper which came originally from the visual examination of a large number of thunderstorms is that an initial positive differential reflectivity zdr associated with supercooled raindrops evolved to reduced zdr and even negative values in the cloud layer between 0 and to 15 c before and during the time of the initial lightning suggesting evolution from supercooled raindrops to frozen particles promoting the formation of the conical graupel an enhanced negative specific differential phase kdp down to 0 5 km 1 in the glaciated layer above 40 c was predominantly observed at the time of the first cg flash indicating that ice crystals such as plates and columns were being vertically aligned by a strong electric field these results demonstrate that the observations of zdr evolution in the mixed layer and negative kdp in the upper levels of convective cores may provide useful information on thunderstorm vigor and lightning nowcasting

geotechnical and groundwater geophysics because of a change in emphasis from power plant siting to projects principally involving process and facility monitoring and certification of existing structures dams pipelines etc geotechnical and groundwater geophysics is in quite a healthy state after some lean years following the demise of nuclear energy construction projects the orders of magnitude jump in the computational capability of geophysicists working in these fields has overshadowed advances in instrumentation e g digital enhancement seismographs field methods e g cross borehole em and interpretive procedures the advent of powerful affordable microcomputers has enabled expansion into applications demanding finer resolution and quicker turnaround of results as a result shallow seismic reflection seismic and electromagnetic geotomography and the complementary use of surface and borehole electrical resistivity and seismic data will soon be common if not dominant methods in geotechnical and groundwater investigations fut

interaction between the chile ridge and chile trench geophysical and geothermal evidence geophysical and geothermal data are examined from the three southernmost sections of the chile ridge starting at 44 s and continuing south to the triple junction of the nazca antarctic and south america plates at 47 s these sections represent three progressively younger stages in a ridge trench collision event corresponding to 3 m y before the collision 1 m y before the collision and culminating in an ongoing collision at the triple junction magnetic and bathymetric data across the chile rise indicate that there is little change in the configuration of the spreading center as the ridge approaches and then collides with the trench in the collision zone a normal looking rift valley can be traced for 40 km before it disappears beneath the toe of the landward trench slope there is no evidence for the complex pattern of ridge jumps and spreading center rotations that occurred when the pacific farallon spreading center collided with north america in contrast the overriding plate is greatly affected by the ridge collision the landward trench slope steepens and narrows as the collision zone is approached at the southern end of the collision zone a ridge associated with the taitao fracture zone is colliding with the trench and may be in the process of being obducted onto the landward trench slope geothermal measurements were made along three transects of the margin corresponding to the time 3 m y before the collision during the collision and 6 m y after the collision the heat flow measurements in the collision zone document a large pulse of heat associated with the subduction of the ridge values as high as 345 mw m2 were recorded on the lower trench slope a prominent bottom simulating reflector bsr observed over a wide area of the landward trench slope north of the triple junction and more locally south of the triple junction is used to expand the grid of heat flow observations excellent agreement is found between measured heat flow and estimates of heat flow based on the depth to the bsr the heat flow measurements compare favorably with a theoretical model assuming conductive heat flow we estimate that the accretionary prism has been substantially removed in the collision zone and conclude that the landward trench slope is undergoing an episode of rapid tectonic erosion periodic ridge collisions in the past may account for the apparent truncation of the andean forearc region

influence of a river plume on coastal upwelling dynamics importance of stratification abstractsatellite images show that the pearl river plume is entrained into the upwelling front in the northeastern south china sea to understand the processes and extend to other coastal zones an

secular variation of archaeomagnetic direction in the american southwest a d 750 1425 oriented archaeomagnetic samples were collected from 158 in situ features at 33 archaeological sites in the southwestern united states seventy three independently dated features were used for analysis of secular variation a moving window technique with outlier rejection was developed to compute a smoothed secular variation curve this technique incorporates weighted fisher statistics to account for imprecision in both the age of remanence acquisition and the direction of magnetization for each feature a mean direction and measure of dispersion is generated for each window of time the secular variation record covers the period a d 750 1425 during which time the virtual geomagnetic pole vgp moves in a generally counterclockwise fashion from 86 n 83 e at a d 750 to the lowest latitude position of 74 n 192 e at a d 1075 and then to 85 n 236 e at a d 1425 the median rate of vgp movement is 0 036 yr 1 similar to present day rates the southwestern record shows close correspondence to other north american archaeomagnetic limnomagnetic and speleomagnetic records the archaeomagnetic record can serve as the master curve for the derivation of archaeomagnetic dates