subaqueous explosive eruption and welding of pyroclastic deposits silicic tuffs infilling an ancient submarine caldera at mineral king in california show microscopic fabrics indicative of welding of glass shards and pumice at temperatures 500 degrees c the occurrence indicates that subaqueous explosive eruption and emplacement of pyroclastic materials can occur without substantial admixture of the ambient water which would cause chilling intracaldera progressive aggradation of pumice and ash from a thick fast moving pyroclastic flow occurred during a short lived explosive eruption of approximately 26 cubic kilometers of magma in water 150 meters deep the thickness high velocity and abundant fine material of the erupted gas solids mixture prevented substantial incorporation of ambient water into the flow stripping of pyroclasts from upper surfaces of subaqueous pyroclastic flows in general both above the vent and along any flow path may be the main process giving rise to buoyant convective subaqueous eruption columns and attendant fallout deposits

nonlinear frequency dependence of the effective seabottom acoustic attenuation from low frequency field measurements in shallow water hamilton s seabed geo acoustic model which is widely accepted predicts that the attenuation of sound in marine sediments increases linearly with frequency over the full frequency range of interest in ocean acoustics a few hertz to megahertz however biot stoll s physics based seabed geo acoustic model predicts that the bottom attenuation should exhibit non linear frequency dependence particularly in sandy bottoms since the publication of previous papers zhou j acoust soc am 78 1003 1009 1985 kibblewhite ibid 86 716 738 1989 more low frequency field data collected from different coastal zones around the world have shown inconsistencies with the often used linear frequency dependence this paper attempts to support the non linear frequency dependence of sea bottom attenuation through a review of shallow water acoustic field measurements with a special emphasis on the 50 1000 hz frequency range the relevant measurements include bottom reflection loss sound transmission loss dispersion analysis vertical coherence of both propagation and reverberation normal mode spatial filtering and optimum frequency and transition range of sound propagation a non linear frequency dependence of equivalent bottom acoustic attenuation derived from these measurements will be introduced work supported by onr and nnsf of china

observations of a colorado tornado part ii combined photogrammetric and doppler radar analysis abstract an integrated analysis of photographic and doppler radar observations of a tornadic storm during the convection initiation and downburst experiment cinde is presented high resolution single doppler radar measurements are combined with cloud photogrammetry to reveal the detailed structural relationship of the hook echo and the misocyclone with visual features of the tornado vertical cross sections of dual doppler winds in the plane of the photographs were also examined to determine the complex motions within and surrounding the vortex the tornado was found to be within a weak echo hole of the hook echo the hole progressed upward above cloud base as the tornado matured an annulus of higher reflectivity that formed a book echo is hypothesized to have been composed of sparse but large raindrops the airflow fields suggest that vortex breakdown and axial downdrafts were present near the ground at early stages shortly after the tornado became visible later axial upward flow dominated at all le

doppler radar analysis of a low precipitation severe storm abstract this is a detailed study of the structure and evolution of a convective storm that formed along the dryline in oklahoma on 26 april 1984 and developed into a supercell dual doppler wind analyses analyses of surface mesonetwork and instrumented tower data storm intercept photographs analyses of raingage data from a dense network and storm reports are presented and discussed the storm exhibited the following low precipitation lp characteristics the absence of any strong evaporatively cooled storm scale downdraft near the surface a paucity of rain reaching the ground large hail long lived rotating updrafts and a strong relatively small in areal extent unicellular radar echo the storm split and its right moving member developed into an isolated high precipitation supercell it is suggested that the region under cloud base was associated with strong radar echo caused by widely spaced large water droplets and hailstones separate cyclonically and anticyclonically rotating updrafts

geoacoustic inversion of broadband data by matched beam processing this paper describes results of geoacoustic inversion using broadband signals from an experiment carried out at a site near the south florida ocean measurement centre in the florida straits m sequence coded pulse trains at different center carrier frequencies from 100to3200hz were recorded at a vertical line array at a distance around 10km geoacoustic inversion was carried out to determine the feasibility of inverting the environmental parameters from this long range propagation experiment the received signal at lower frequencies below 400hz consisted of a dominant water column signal and a secondary arrival delayed by 0 4s the secondary signal was spatially filtered by beamforming the array data and the beam data were inverted by matched beam processing in the time domain combined with an adaptive simplex simulated annealing algorithm the estimated values of compressional wave speed and density were in good agreement with ground truth values from sediment cores the inverted shear wave speed appea

the 8 june 1995 mclean texas storm part i observations of cyclic tornadogenesis abstract on 8 june 1995 scientists participating in the verification of the origins of rotation in tornadoes experiment vortex collected airborne doppler radar data in a storm that produced a family of tornadoes near mclean texas the electra doppler radar eldora scanned three significant tornadoes during their formative and mature stages one of the tornadoes was of f4 f5 intensity evidence from pseudo dual doppler analyses of the eldora data reveals a process of cyclic tornado formation qualitatively similar to that depicted in previous conceptual models in particular the rear flank gust front appears to play a major role in determining the location of the next vortex in the series when a tornado forms a small region 3 5 km wide of outflow surges ahead of the tornado producing a local bulge in the gust front a new vorticity maximum may form near the leading edge of the outflow in contrast to what is suggested by earlier conceptual models intersection of the rear flank gust front with a w

doppler radar wind spectra of supercell tornadoes abstract a storm intercept team from the university of oklahoma using the los alamos national laboratory portable continuous wave frequency modulated continuous wave 3 cm doppler radar collected close range data at and below cloud base in six supercell tornadoes in the southern plains during the springs of 1990 and 1991 data collection and analysis techniques are described wind spectra from five weak to strong tornadoes and from one violent tornado are presented and discussed in conjunction with simultaneous boresighted video documentation photogrammetric analysis and damage surveys maximum doppler wind speeds of 55 105 m s 1 were found in five of the tornadoes wind speeds as high as 120 125 m s were found in a large tornado during an outbreak on 26 april 1991 these may be the highest wind speeds ever measured by doppler radar and the first radar measurements of f 5 intensity wind speeds the variation in the spectrum across the 26 april 1991 tornado is presented standard and mobile soundings

observations related to the rotational dynamics of the 20 may 1977 tornadic storms abstract observations of the 20 may 1977 tornadic storms are used to evaluate recent theories on the initiation of rotation at mid and low levels and to verify recent thermodynamic retrieval results using the lengthy data record from a variety of sensors available for this day it appears that the mechanism that initiates low level rotation is different from that at midlevels attempts to identify the source of the low level rotation as vertical tilting baroclinically generated horizontal vorticity were inconclusive the recent thermodynamic retrieval results of hane and ray and of brandes for these storms are in good agreement with independent measurements where available however verification is hindered by the sparseness of these measurements noticeable differences in the region of the rear flank downdraft suggest that there is room for improvement in the retrieval methods investigation of the cyclic generation of rotation along gust fronts indicates that the source of low level rotation is not der

a study of the tornadic region within a supercell thunderstorm abstract the transition of a supercell thunderstorm into its tornadic phase is investigated through high resolution numerical cloud model simulations initiated within the interior portion of a previously simulated mature supercell storm with the enhanced grid resolution the low level cyclonic vorticity increases dramatically and the gust front rapidly occludes as small scale downdrafts develop in the vicinity of the low level center of circulation as the occlusion progresses a ring of high vorticity air surrounds the circulation center and could be conducive to multiple vortex tornado formation numerous features of the simulated transition bear resemblance to those observed in tornadic storms in the model simulation the large low level vorticity is generated through the tilting and intense stretching of air from the inflow side of the storm this vertical vorticity is derived from the horizontal vorticity of the environmental shear and also from horizontal vorticity generated solenoidally as low l

airborne doppler radar analysis of supercells during cops 91 abstract on 26 may 1991 noaa p 3 airborne doppler radar data were collected near two tornadic supercells in the southern plains during the cooperative oklahoma profiler studies cops 91 field program the 3 cm radar mounted in the tail of the aircraft was operated using the fore aft scanning technique fast both storms were sampled just minutes after each had produced a tornado the cops 91 storms are the first tornadic supercells to be sampled extensively by airborne doppler radar using the fast methodology pseudo dual doppler analyses of a dissipating storm in southwest kansas show no remaining low level circulation even though the storm had just produced a tornado the analyses of a storm in northwest oklahoma reveal better defined features in the wind field near the surface in contrast to what has been previously observed in post tornadic supercells the cyclonic vorticity in both storms was greater aloft than at low levels the 26 may 1991 storms provide further evidence that supercells often

a numerical simulation of cyclic mesocyclogenesis abstract a three dimensional nonhydrostatic numerical model the advanced regional prediction system is used to study the process of cyclic mesocyclogenesis in a classic supercell thunderstorm during the 4 h simulation the storm s mesocyclone undergoes two distinct occlusions with the beginning of a third indicated at the end of the simulation the occlusion process exhibits a period of approximately 60 min and is qualitatively similar in each case initial midlevel 3 7 km mesocyclogenesis proceeds according to the classic picture that is via tilting of streamwise environmental vorticity the development of an evaporatively driven rear flank downdraft rfd signals the beginning of the occlusion process the developing rfd wraps cyclonically around the mesocyclone causing the gust front to surge outward simultaneously the occluding mesocyclone rapidly intensifies near the surface trajectory analyses demonstrate that this intensification follows from the tilting and stretching of near ground

airborne pseudo dual doppler analysis of a rear inflow jet and deep convergence zone within a supercell abstract on 22 may 1995 numerous thunderstorms several of which produced large hail and small tornadoes formed along a dryline in the central and northern texas panhandle the only long lasting daytime severe storms developed later south of the earlier storms by late afternoon new cells merged and evolved into two large supercells the northern supercell produced three weak tornadoes and hail the southern supercell did not produce a tornado but did produce very large hail for an extended period of time verification of the origins of rotation in tornadoes experiment crews collected data in the southern supercell from its early stage through much of its mature stage the national center for atmospheric research electra doppler radar collected pseudo dual doppler radar data on this storm continuously for well over an hour detailed analyses of this high resolution dataset revealed several unusual features most notably an intense elevated rear inflow jet at midlevels having maximum wind speeds app

the san angelo texas supercell of 31 may 1995 visual observations and tornadogenesis abstract airborne radar analysis combined with cloud photogrammetry of a supercell that formed on 31 may 1995 near san angelo texas is presented the superposition of the doppler wind syntheses with the cloud pictures provides a unique view of the relationship between the low level mesocyclone and the developing lowered cloud base the mesocyclone accompanying the storm went through two periods of intensification the end of the first period of intensification did not lead to the formation of a tornado an occlusion downdraft formed but was primarily driven by negative buoyancy rather than a downward directed perturbation pressure gradient recent studies have suggested that cold downdrafts inhibit the formation of tornadoes the present study supports this hypothesis and provides the first quantitative view of the vertical structure of this downdraft the mesocyclone evolved through a second period of intensification that produced a weak tornado that was visually apparent from the aircraft no occlusio

mesoscale and convective scale characteristics of mature hurricanes part i general observations by research aircraft abstract the analysis of instrumented aircraft data from four recent mature hurricanes reveals common mesoscale and convective scale features the structure and organization of the convection precipitation and wind flow are studied by combining the airborne observations using basic instrumentation with quantitative radar measurements three predominant precipitation features seen are 1 the eyewall 2 a stratiform rain region adjacent to and outside the eyewall and 3 rainbands that contain both convective and stratiform regions the eyewall is so named because it surrounds the rain free eye but several additional features distinguish it from other convective bands in the hurricane in particular the updraft tangential wind maximum and highest rainfall have preferred locations relative to each other with the updraft being radially inward from the rain and wind maxima the 10 dbz radar reflectivity contour indicative of the inner edge slopes substantially outward with height and there is evide

precipitation and kinematic structure of an oceanic mesoscale convective system part i convective line structure abstract the precipitation thermodynamic and kinematic structure of an oceanic mesoscale convective system is studied using airborne doppler and in situ flight level data collected by the noaa p 3 aircraft the system a well organized stationary north south convective line was located near the east coast of taiwan in part i the basic structure of the line is documented with both datasets a procedure revealing the strengths and weakness of both approaches the doppler data reveal that the warm moist air feeding the line enters from the east side most updrafts associated with the leading edge of the convective line tilt westward below 5 km and then eastward above 5 km this change of tilt corresponds to a change in the sign of the vertical flux of east west momentum to the east of the leading edge a 10 km wide zone of strong mesoscale descent is seen the band is not a complete barrier to the low level southeasterly flow and at times and places along the line the inflowing air can move throu

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

the 8 june 1995 mclean texas storm part ii cyclic tornado formation maintenance and dissipation abstract on 8 june 1995 scientists participating in the verification of the origins of rotation in tornadoes experiment vortex collected a unique dataset with the electra doppler radar eldora the eldora observations document the sequential life cycles of storm scale circulations associated with three large tornadoes in a supercell thunderstorm near mclean texas a qualitative description of the evolution of the storm was provided in part i of this paper during the first stage of development of each storm scale circulation interaction of the updraft with the environmental low level horizontal vorticity produced a vorticity column that increased in intensity with height as the vortex matured vorticity increased greatly at low levels i e below 2 km agl and exceeded that aloft each tornadic vortex was located near the rear side of the updraft where the surrounding low level horizontal vorticity was modified locally most likely by weak baroclinity within the storm tilting of low level horizo

new field and laboratory evidence for the origin of hyaloclastite flows on seamount summits new field observations with the submersible alvin and photographic evidence from a study of the summits of seamounts near the east pacific rise show that hyaloclastite deposits occur commonly hyaloclastite outcrops were found on six volcanoes at depths from 1240 to 2500 m these new observations plus laboratory study of new hyaloclastite specimens extend the results of previous studies most of the hyaloclastite samples are of hydrovolcanic eruptive origin but a few show evidence of a predominantly sedimentary origin primarily from morphology we identify several vent areas from which hyaloclastite presumably erupted the surface appearance of the hyaloclastite deposits varies with distance to these vents leading us to propose a facies model for deep sea hyaloclastites on seamount summits hyaloclastites of hydromagmatic origin exhibit weak normal grading and bedding parallel alignment of platy shards they consist of blocky sliver and fluidal basalt glass shards and lithics in a matrix that contains pelagic sediment the shards themselves are remarkably free of even the tiniest crystals and are usually chemically homogeneous we propose that the shards form mainly by cooling contraction granulation but cannot rule out the possibility of limited steam explosivity hyaloclastites are closely associated with submarine pahoehoe and we propose that a very rapid eruption rate promoting clastic dominated versus flow dominated eruptive behavior is the dominant control on hyaloclastite formation we propose that shard formation occurs during submarine lava fountaining gravitational instability of the resulting slurry of shards sea water and possibly steam causes gravity flow that carries the shards outward from the vent further field and modelling studies are needed to test these ideas and more quantitatively constrain the ascent mechanism eruption dynamics and deposition of deep sea hyaloclastites

pressure at the ground in a large tornado a number of instruments were placed on the ground across the path of a large tornado that passed west of the town of allison texas on june 8 1995 the center of the tornado came within 660 m of the closest instrument which recorded a pressure drop of 55 mbar and a subsequent pressure rise of 60 mbar during the lowest recorded pressures near r 660 m there were large and rapid pressure fluctuations the largest fluctuation was a 10 mbar spike lasting 2 s a second instrument on the opposite side of the tornado recorded a pressure drop of 26 mbar from the pressure variations with time p t at the two instruments the variation of pressure with distance p r from the center of the tornado has been deduced for r 660 m as r decreases the measured pressure function p r drops more abruptly than would be expected from conservation of angular momentum of air spiraling inward near the ground level

pressure and buoyancy fields derived from doppler radar data in a tornadic thunderstorm abstract a method for retrieval of pressure and buoyancy distributions in deep convection is applied to doppler radar data collected at two analysis times during the tornadic del city oklahoma thunderstorm of 20 may 1977 change of a previous version of the technique necessitated by application to real data include procedures for handling irregularly bounded volumes and missing data and new assumptions to include reflectivity data and turbulent effects in the equations internal consistency cheeks on the quality of retrieved pressure fields imply that the input data are generally of good quality and point out times and heights within the storm at which greater confidence can be placed in the derived fields in the pretornadic stage the pressure distribution includes at each level a high low couplet across the updraft with the maximum pressure gradient generally oriented along the environmental shear vector at that altitude these results are in agreement with predictions of linear theory locations of

a synoptic and photographic climatology of low precipitation severe thunderstorms in the southern plains abstract the occurrence of an unusual type of severe thunderstorm difficult to identify by radar has been documented in the southern plains all of the three storms previously studied occurred near the dryline although tornadoes and large hail were produced little rain was observed at the ground and there was no evidence of a strong surface downdraft two were described as bell shaped ten more cases of this rare type of storm have been recently documented visually and on radar a photographic and synoptic climatology of this class of storm the low precipitation severe storm is suggested on the basis of an analysis of the comparison among 11 of these cases it is found that these storms form in a supercell like environment which is drier in the moist layer and more weakly sheared than that of well documented supercells in oklahoma implications of our findings and additional storm characteristics are discussed in light of the larger sample size

characteristics of dryline passage during cops 91 abstract the characteristics of dryline passage are documented through an analysis of data from an instrumented surface mesonetwork in the texas panhandle and western and central oklahoma during the cooperative oklahoma profiler studies field program some eastward moving drylines at the surface during the day were characterized by monotonic drops in dewpoint after dryline passage others were marked by a series of rapid drops punctuated by periods of no change after dryline passage which suggests that the dryline often progresses in discrete steps rather than continuously the dryline during the daytime was not always collocated with a pressure trough although the strongest dryline observed was analyses of surface pressure traces indicated that westward moving drylines during the evening did not display behavior characteristic of strong intense density currents as had been found in other studies evidence is presented in one case of 90 min oscillations in water vapor and wind behind the dryline

the submarine eruption and emplacement of the lower rhyolitic tuff formation ordovician n wales the lower rhyolitic tuff formation up to 600 m thick represents an eruptive cycle of acidic ash flow tuff which is stratigraphically associated with marine sediments and subaqueously emplaced basalt lavas the formation comprises volcaniclastic and pyroclastic megabreccias and breccias massive welded and non welded acidic ash flow tuffs reworked tuffs and tuffities siltstones rhyolite intrusions and extrusions its basal contacts vary from conformable to disconformable and unconformable the inter relationships of these variations to pre syn and post emplacement structures define a submarine asymmetric downsag caldera the main eruptive centre coincident with the thickest accumulation of intracaldera tuffs lies close to its north margin on the north side of the snowdon massif to the sw the intracaldera tuffs thin progressively and much of the formation comprises tuffs reworked in the vicinity of a caradocian shoreline to the ne and e outflow tuffs escaped into a deeper marine basin many of the features of the caldera are similar to those of subaerial calderas and it is concluded that the enveloping sediments and lavas and the character of the reworked tuffs hold the key to the recognition of its submarine development subsequent resurgence resulted in only local and short lived emergence of the intracaldera tuffs

precipitation and kinematic structure of an oceanic mesoscale convective system part i momentum transport and generation abstract this is the second paper of a two part series documenting the structure of and momentum transport by a subtropical mesoscale convective system near taiwan using doppler radar data and in situ data from the noaa p 3 part i defines the basic system structure and evolution in part ii the momentum transport by the system is estimated and related to system structure and the momentum budget for a portion of the embedded convective band is evaluated profiles of the vertical flux of horizontal momentum are constructed from in situ data doppler radar data and both combined in a coordinate system with u normal to the line and positive eastward since the low level air is feeding the line from the east differences in the fluxes from the two sources appear to be mainly due to an underestimation of the mean vertical velocity from the doppler radar data the discrepancy results partially from the concentration of convergence in the boundary layer precisely where the doppler cannot adequately sample t

submarine silicic volcanism and associated sedimentary and tectonic processes ramsey island sw wales lower ordovician marine strata formed in an ensialic marginal basin environment record early episodes of distant explosive silicic volcanism and a later volcanotectonic episode which was a precursor to the development of a wide variety of near to source submarine silicic volcanic phenomena the early episodes are represented by well bedded turbiditic tuffs these and older strata at least 770 m thick in normal stratigraphical succession are allochthonous and large scale wet sediment sliding with reworking of strata in cohesive debris flows reflects major disturbance of the sea floor during the emplacement of silicic magmas volcanotectonic uplift along a n s fault exceeded 1 km and led to the emergence and erosion of a rhyolitic volcanic island this was followed closely by submergence and in water depths perhaps of about 500 m there accumulated welded and non welded rhyolitic ash flow tuffs rhyolitic turbiditic tuffs rhyolite lavas and a wide variety of debris flow deposits shallow intrusions of 9low9 viscosity rhyolite were emplaced contemporaneously the more or less simultaneous emplacement of rhyolitic tuff with both 9low9 viscosity and high viscosity rhyolites is attributed to variable water content related perhaps to volatile fluxing in a magma body the location of the near to source extrusive rocks and consanguineous intrusions along the contemporary n s fault is considered to reflect channelling of magma initially along a deep crustal fracture

hook echoes and rear flank downdrafts a review abstract nearly 50 years of observations of hook echoes and their associated rear flank downdrafts rfds are reviewed relevant theoretical and numerical simulation results also are discussed for over 20 years the hook echo and rfd have been hypothesized to be critical in the tornadogenesis process yet direct observations within hook echoes and rfds have been relatively scarce furthermore the role of the hook echo and rfd in tornadogenesis remains poorly understood despite many strong similarities between simulated and observed storms some possibly important observations within hook echoes and rfds have not been reproduced in three dimensional numerical models

marine emplacement of welded ignimbrite the ordovician pitts head tuff north wales the pitts head welded ignimbrite records a subaerial large volume eruption and associated pyroclastic current that flowed into the sea the current 15 km from source was steadily sustained with high mass flux and high particle concentration towards its base and it entered the sea without substantial mixing with water and thus without large scale hydroexplosivity and without general cooling it continued to aggrade ignimbrite at 580 c for at least 3 4 km from the original shoreline in water initially 50 m deep entirely subaqueous hot state progressive aggradation and welding of the ignimbrite occurred where the water could not be wholly displaced by the current although eventually the deposit displaced the shore 4 km seawards wet sea floor sediments buried by the ignimbrite were heated and locally fluidized by steam and several square kilometres of hot ignimbrite with variable thicknesses of sedimentary substrate detached and slid downslope directions of sliding and the order of piling up of slide sheets are shown by hot state rheomorphic deformation fabrics and the geometric relations of detachment surfaces extensional disruption of the ignimbrite is marked by breaks in the sheet via which fluidized sediments were mobilized locally to form rootless vents both the initial incursion of the pyroclastic current into the sea and the subsequent submarine sliding of the ignimbrite are likely to have caused tsunamis similar occurrences at modern coastlines presently susceptible to incursion of high mass flux pyroclastic currents e g taupo volcanic zone new zealand neapolitan region italy vicinity of manila taal philippines would according to tsunami propagation behaviour cause significant near and far field coastal hazard

quantifying the uncertainty of geoacoustic parameter estimates for the new jersey shelf by inverting air gun data this paper describes geoacoustic inversion of low frequency air gun data acquired during an experiment on the new jersey shelf hybrid optimization and bayesian inversion techniques based on matched field processing were applied to multiple shots from three air gun data sets recorded by a vertical line array in a long range shallow water geometry for the bayesian inversions full data error covariance matrix was estimated from a set of consecutive shots that had high temporal coherence and small spatial variation in source position the effect of different data error information on the geoacoustic parameter uncertainty estimates was investigated by using the full data error covariance matrix a diagonalized version of the full error covariance and a diagonal matrix with identical variances the comparison demonstrated that inversion using the full data error information provided the most reliable parameter uncertainty estimates the inversions were highly sensitive to the near sea floor geoacoustic parameters including sediment attenuation of a simple single layer geoacoustic model the estimated parameter values of the model were consistent with depth averaged values over wavelength scales of a high resolution geoacoustic model developed from extensive ground truth information the interpretation of the frequency dependence of the estimated attenuation is also discussed

a nonclassical cold front observed during cops 91 frontal structure and the process of severe storm initiation abstract this case study addresses the issue of gravity current and bore development at surface cold fronts and the role of these phenomena in the generation of severe frontal convection the event investigated occurred on 27 april 1991 during the cooperative oklahoma profiler studies 1991 field project the development of a bore from a gravity current like structure along a cold front the subsequent propagation of the bore ahead of the front on a low level inversion and the process of severe thunderstorm development along the front are revealed by a dense network of remote sensing and other special observations evidence for the gravity current and bore is strengthened by comparisons made between the synthesized observations and theory the bore developed after a nocturnal inversion which acted as a waveguide had become established the bore and gravity current were both evident as fine lines in the radar reflectivity displays a microscale envelope of enhanced water vapor with an embedded roll cl

the arcadia oklahoma storm of 17 may 1981 analysis of a supercell during tornadogenesis abstract on 17 may 1981 an extensive dataset was collected for a supercell thunderstorm that produced an f2 tornado near arcadia in central oklahoma coordinated dual doppler scans of the storm by 10 cm research radars were collected at approximately 5 min intervals from 30 min before the tornado touched down until 15 min after the tornado had dissipated the arcadia storm was also well sampled by a 444 m tall instrumented tower the low level inflow updraft mesocyclone and rear precipitation core of the supercell all passed across the tower a comparison of the instrumented tower measurements with a dual doppler synthesis reveals that the latter qualitatively resolved the low level flow however the magnitudes of the low level horizontal winds and updraft speed were underestimated in addition the vertical shear of the horizontal wind in the lowest kilometer was unresolved in the doppler winds in the storm environment horizontal vorticity was strong 1 5 10 2 s 1 and approximately streamwise

statistical analysis of sound transmission results obtained on the new jersey continental shelf experiments have been conducted near the site of amcor borehole 6010 on the new jersey shelf to evaluate propagation predictability in sandy shallow water environments the influence of a nonlinear frequency dependence of the sediment volume attenuation in the uppermost sediment layer at this location is examined previously it was determined that a frequency power law exponent of 1 5 was required for the best modeling of experimental results over the band 50 1000hz the approach here references the attenuation to an accepted value at 1khz and makes extensive comparisons between measurements and calculations to determine a power law exponent of 1 85 0 15

the dali ash island of rhodes greece a problem in interpreting submarine volcanigenic sediments in the southern part of rhodes greece rhyolitic subaqueous pyroclastic deposits are interbedded with tertiary deep water marine sediments the lowermost and best exposed of these deposits the dali ash is described here the deposit has been previously described as a deep water welded subaqueous ignimbrite this paper shows that there is no evidence of welding and texture previously reported were misidentified the dali ash consists of a lower massive unit 5 m thick overlain by a sequence of ash turbidites 2 5 m thick the lower unit was deposited by a high concentration turbidity current and the ash turbidites by dilute turbidity currents foraminifera are dispersed throughout the deposit and indicate that all the sedimentary gravity flows were cold water particulate systems a palaeomagnetic study also suggests they were deposited cold