in situ measurements of velocity dispersion and attenuation in new jersey shelf sediments the existence of acoustic velocity dispersion and frequency dependence of attenuation in marine sediments is investigated using in situ measurements from a wideband acoustic probe system during the shallow water 2006 experiment direct path pulse propagation measurements show evidence of velocity dispersion within the 10 80khz frequency band at two silty sand sites on the new jersey shelf the measured attenuation in db m shows linear frequency dependency within the 10 80khz frequency band the measured velocity dispersion and attenuation curves are in good agreement with those predicted by an extended biot theory yamamoto and turgut j acoust soc am 83 1744 1751 1988 for sediments with a distribution of pore sizes

the annual cycle in equatorial convection and sea surface temperature abstract the coupled atmosphere ocean system in the equatorial eastern pacific and atlantic exhibits a distinct annual cycle that is reflected in contrasting conditions at the times of the two equinoxes the contrasts are so strong that they dominate the annual march of zonally averaged outgoing longwave radiation for the equatorial belt the march equinox corresponds to the warm season when the equatorial cold tongues in the eastern pacific and atlantic are absent with the onset of summer monsoon convection over colombia central america and west africa in may june northward surface winds strengthen over the eastern pacific and atlantic the equatorial cold tongues reappear and the marine convection shifts from the equatorial belt to the intertropical convergence zones itczs along 8 n as the northern summer program the itczs remain strong and shift northward to new 10 n while sea surface temperature sst continues to drop over the cold tongues and the southern tropics perhaps in response to the

near bed mass flux profiles in aeolian sand transport high resolution measurements in a wind tunnel vertical profiles of the streamwise mass flux of blown sand in the near bed 17 mm region are analysed from high resolution measurements made using an optical sensor in a wind tunnel this analysis is complemented by detailed measurements of mass flux and mean velocity profiles throughout the boundary layer depth 0 17 m using passive chambered sand traps of small dimensions and armoured thermal anemometers respectively the data permit a preliminary analysis of the relations between the observed forms of the profiles of near bed fluid stress and horizontal mass flux within a carefully conditioned boundary layer profiles of mass flux density are found to be characterized by three regions of differing gradient with transitions at about 2 mm and 19 mm above the bed the exponential decay of mass flux with height is confirmed for elevations above 19 mm and when plotted as a function of u 2 g a parameter of mean vertical trajectory height in saltation the gradient of mass flux in this region scales with the wake corrected friction velocity u where u 0 30 m s 1 a separate near bed region of more intense transport below 19 mm is identified which carries 80 per cent of the total mass flux this region is evident in some previous field and wind tunnel data but not in profiles simulated by numerical models ventilated passive sand traps underestimate mass flux in this region by 37 per cent at slow or moderate wind speeds a third significant region below 2 mm is observed these regions are likely to be related to grain populations in successive saltation low energy ejections and intermittent bed contact respectively optical measurements reveal locally high grain concentrations at some elevations below 5 mm these heights scale with transport rate mass flux gradient and wind speed copyright 1999 john wiley sons ltd

grain size and transport characteristics of non uniform sand in aeolian saltation abstract size frequency distributions of sediment particles in a wind tunnel containing a bed of non uniform sand are investigated by re interpreting existing experimental data using particle size analysis each particle sample is classified into one of eight groups according to its size grading the analysis reveals that the modal shape of the particle size frequency distributions of the saltating sand at different elevations or longitudinal distances is similar to that of the mixed sand in the bed once the boundary layer is fully developed the standard deviation of the grain size frequency distribution increases with increasing elevation above the bed then stays constant whereas its skewness decreases the mean grain size decays exponentially with elevation the aeolian sand mass flux is determined for each size grading at different vertical and horizontal measurement locations the vertical profile of aeolian horizontal mass flux depends on the size grading the distribution of the sand transport rate according to the mean grain size in each grading fits the normal distribution a parameter w i is defined to reflect the likelihood of saltation for sand particles of the i th size grading and the mean sand size corresponding to the maximum value of w i is found to be 0 2 mm in addition wind velocity strongly influences the magnitudes of the particle size distribution and the sand mass flux distribution in both vertical and longitudinal directions

convective momentum transport associated with the madden julian oscillation based on a reanalysis dataset abstracta better understanding of multiscale interactions within the madden julian oscillation mjo including momentum exchanges is critical for improved mjo prediction skill in this study convective momentum transport cmt associated with the mjo is analyzed based on the noaa climate forecast system reanalysis cfsr a three layer vertical structure associated with the mjo as previously suggested in the mesoscale momentum tendency profile based on global cloud resolving model simulations is evident in the subgrid scale momentum tendency from the cfsr positive negative subgrid scale momentum tendency anomalies are found near the surface negative positive anomalies are found in the low to midtroposphere and positive negative anomalies in the upper troposphere are found within and to the west east of the mjo convection this tends to damp the mjo circulation in the free atmosphere while enhancing mjo winds near the surface in addition it could also reduce the mjo eastward propagation

mid frequency geoacoustic inversion using bottom loss data from the shallow water 2006 experiment geoacoustic inversion work has typically been carried out at frequencies below 1 khz assuming flat horizontally stratified bottom models despite the relevance to navy sonar systems many of which operate at mid frequencies 1 10 khz limited inversion work has been carried out in this frequency band this paper is an effort to demonstrate the viability of geoacoustic inversion using bottom loss data between 2 and 5 khz the acoustic measurements were taken during the shallow water 2006 experiment off the coast of new jersey a half space bottom model with three parameters density compressional wave speed and attenuation was used for inversion by fitting the model to data in the least square sense inverted sediment sound speed and attenuation were compared with direct measurements and with inversion results using different techniques carried out in sw06 inverted results of the present work are consistent with other measurements considering the known spatial variability in this area the observations and modeling results demonstrate that forward scattering from topographical changes is important at mid frequencies and should be taken into account in sound propagation predictions and geoacoustic inversion to cope with fine scale topographic variability measurement technique such as averaging over tracks may be necessary

vertical structures of anvil clouds of tropical mesoscale convective systems observed by cloudsat abstracta global study of the vertical structures of the clouds of tropical mesoscale convective systems mcss has been carried out with data from the cloudsat cloud profiling radar tropical mcss are found to be dominated by cloud top heights greater than 10 km secondary cloud layers sometimes occur in mcss but outside their primary raining cores the secondary layers have tops at 6 8 and 1 3 km high topped clouds extend outward from raining cores of mcss to form anvil clouds closest to the raining cores the anvils tend to have broader distributions of reflectivity at all levels with the modal values at higher reflectivity in their lower levels portions of anvil clouds far away from the raining core are thin and have narrow frequency distributions of reflectivity at all levels with overall weaker values this difference likely reflects ice particle fallout and therefore cloud age reflectivity histograms of mcs anvil clouds vary little across the tropics except that i in continental mcs anvils

3d ejection behavior of different sized particles in the grain bed collision process abstract the impact ejection process on a mixed grain size bed with granular packing was simulated with the discrete element method in order to understand the interaction between different sized grains in natural aeolian sand transport in this model the granular bed was formed by settling the randomly generated two sized particles under gravity and then a foreign particle was shot onto the granular bed at different speeds and angles the recorded speed direction and number of the ejected particles were then analyzed it was found that the probability distributions of the ejection speed and angle for different sized particles are all identical to those for the single size grain bed collision process the mean ejection speeds of different sized particles are nearly equal and the mean ejection angles of different sized particles are all equal to a constant of 60 the average number of each size of ejected particles grows linearly with the increasing impact speed but remains invariant for various impact angles moreover the smaller particles are preferentially ejected and the ratio between the mean numbers of different sized particles is independent of both the impact speed and angle additionally the ejected particles were found to move in a 3d space they become distributed symmetrically around the incident plane and jump not only forward but also backward these results are critical to understanding the grain size induced inhomogeneity in aeolian sand transport

monsoon convection in the himalayan region as seen by the trmm precipitation radar three dimensional structure of summer monsoon convection in the himalayan region and its overall variability are examined by analyzing data from the tropical rainfall measuring mission trmm precipitation radar over the june september seasons of 2002 and 2003 statistics are compiled for both convective and stratiform components of the observed radar echoes deep intense convective echoes 40 dbz echo reaching heights 10 km occur primarily just upstream south of and over the lower elevations of the himalayan barrier especially in the northwestern concave indentation of the barrier the deep intense convective echoes are vertically erect consistent with the relatively weak environmental shear they sometimes extend above 17 km indicating that exceptionally strong updraughts loft graupel to high altitudes occasionally scattered isolated deep intense convective echoes occur over the tibetan plateau wide intense convective echoes 40 dbz echo 1000 km2 in horizontal dimension also occur preferentially just upstream of and over the lower elevations of the himalayas most frequently in the northwestern indentation of the barrier the wide intense echoes have an additional tendency to occur along the central portion of the himalayas and they seldom if ever occur over the tibetan plateau the wide intense echoes exhibit three mesoscale structures amorphous areas lines parallel to the mountain barrier and arc shaped squall lines perpendicular to and propagating parallel to the steep himalayan barrier the latter are rare generally weaker than those seen in other parts of the world and occur when a midlevel jet is aligned with the himalayan escarpment deep and wide intense convective echoes over the northwestern subcontinent tend to occur where the low level moist layer of monsoon air from the arabian sea meets dry downslope flow in a manner reminiscent of severe convection leeward of the rocky mountains in the central usa as the low level layer of moist air from the sea moves over the hot arid northwestern subcontinent it is capped by an elevated layer of dry air advected off the afghan or tibetan plateau the capped low level monsoonal airflow accumulates instability via surface heating until this instability is released by orographically induced lifting immediately adjacent to or directly over the foothills of the himalayas broad 50 000 km2 in area stratiform echoes occur in the eastern and central portions of the himalayan region in connection with bay of bengal depressions their centroids are most frequent just upstream of the himalayas in the region of the concave indentation of the barrier at the eastern end of the range the steep topography apparently enhances the formation and longevity of the broad stratiform echoes monsoonal depressions provide a moist maritime environment for the convection evidently allowing mesoscale systems to develop larger stratiform echoes than in the western himalayan region copyright 2007 royal meteorological society

winter monsoon convection in the vicinity of north borneo part i structure and time variation of the clouds and precipitation abstract radar and satellite observations in the vicinity of northern borneo obtained during the international winter monsoon experiment wmonex showed that the convection in that region underwent an extremely regular diurnal cycle over the sea to the north of borneo the general level of convective activity was increased during monsoon surges and during the passages of westward propagating near equatorial disturbances convective activity was decreased during monsoon lulls the diurnal cycle was well defined regardless of whether the general level of convective activity was enhanced or suppressed by synoptic scale events the cycle of convection over the sea was especially well documented it was typically initiated at about midnight when an offshore low level wind began where this wind met the monsoonal northeasterly flow usually just off the coast convective cells formed after midnight the convection continued to develop and by 0800 lst it had evolved into an organized mesoscale system with a

properties of tropical convection observed by millimeter wave radar systems abstract this paper describes the results of analysis of over 825 000 profiles of millimeter wave radar mwr reflectivities primarily collected by zenith pointing surface radars observing tropical convection associated with various phases of activity of the large scale tropical circulation the data principally analyzed in this paper come from surface observations obtained at the atmospheric radiation measurement manus site during active and break episodes of the madden julian oscillation mjo and from observations collected from a shipborne radar during an active phase of the monsoon over the indian ocean during the joint air sea monsoon interaction experiment it was shown for example in a histogram regime analysis that the mwr data produce statistics on convection regimes similar in most respects to the analogous regime analysis of the tropical rainfall measuring mission radar radiometer observations attenuation of the surface mwrs by heavy precipitation however incorrectly shifts a small fracti

the precipitating cloud population of the madden julian oscillation over the indian and west pacific oceans 1 the variability of the precipitating cloud population of the madden julian oscillation mjo is represented by statistics of echo features seen by the tropical rainfall measuring mission s precipitation radar over the central indian and west pacific oceans echo features include isolated shallow echoes deep convective cores wide convective cores and broad stratiform regions isolated shallow echoes are ever present but most numerous during suppressed mjo phases broad stratiform regions dominate variability in areal coverage and maximize during active phases deep convective and wide convective cores are more common and variable in number than broad stratiform regions the magnitude of variability is similar in both regions in the central indian ocean active mjo phases have synchronous maximization of deep convective entities in the west pacific broad stratiform regions maximize prior to wide convective cores reanalysis indicates that isolated shallow echoes are most numerous in dry mid tropospheric conditions and strong low level 1000 750 hpa shear mid tropospheric moisture increases before deeper convective features increase in number maximizes as deep convective features maximize and decreases as wide convective cores and broad stratiform regions decline in population active stage deep and wide convective cores occur preferentially with moist mid tropospheric conditions and strong low level shear acute shear may favor downdraft momentum transport and consequently more robust gust front convective triggering broad stratiform regions maximize with a moist mid troposphere strong low level shear and moderate upper level 750 500 hpa shear that is not so strong that the stratiform region disconnects from its convective moisture source

deep convective systems observed by a train in the tropical indo pacific region affected by the mjo abstractin the indo pacific region mesoscale convective systems mcss occur in a pattern consistent with the eastward propagation of the large scale convective envelope of the madden julian oscillation mjo mcss are major contributors to the total precipitation over the open ocean they tend to be merged or connected systems while over the maritime continent area they tend to be separated or discrete over all regions affected by the mjo connected systems increase in frequency during the active phase of the mjo characteristics of each type of mcs separated or connected do not vary much over mjo affected regions however separated and connected mcss differ in structure from each other connected mcss have a larger size and produce less but colder topped anvil cloud for both connected and separated mcss larger systems tend to have colder cloud tops and less warmer topped anvil cloud the maximum height of mcs precipitating cores varies only slightly and the variation is related to sea surface t

anvil productivities of tropical deep convective clusters and their regional differences abstractthe anvil productivities of tropical deep convection are investigated and compared among eight climatological regions using 4 yr of collocated and combined cloudsat and calipso data for all regions the convective clusters become deeper while they become wider and tend to be composed of multiple rainy cores two strong detrainment layers from deep convection are observed at 6 8 km and above 10 km which is consistent with the trimodal characteristics of tropical convection that are associated with different divergence cloud detrainment and fractional cloudiness the anvil productivity of tropical deep convection depends on the convection scale convective life stage or intensity and large scale environment anvil ice mass ratio related to the whole cluster starts to level off or decrease when the cluster effective scales weff the dimension of an equivalent rectangular with the same volume and height as the original cluster increase to about 200 km wide while the ratios of anvil scale and vo

frequency magnitude and characteristics of aeolian sediment transport mcmurdo dry valleys antarctica 1 due in part to the challenging environment of earth s high latitude regions available information on cold climate effects on aeolian processes in these areas remains limited data from these areas however provide insight into the physics of sediment transport by wind and the controls on erosive winds in proximity to ice caps and topographic influences this study presents a 2 year record of meteorological saltation activity horizontal saltation flux and particle size distribution data from four sites in the mcmurdo dry valleys of antarctica 2008 to 2010 saltation measurements revealed daily and seasonal patterns with spring and summer sediment transport events occurring between 09 00 and 24 00 hours due to thermally generated winds fall and winter events occur at any time of day with the strongest associated with foehn winds threshold wind speed at 4 2 m in all seasons for all locations was 10 m s 1 saltation occurred in the temperature range 40 c to 5 c westerly winds in the fall winter and easterly winds in spring summer are associated with the majority of transport events the sand in transport is mainly 250 to 500 m in diameter and poorly sorted the integrated saltation flux varies over three orders of magnitude among the sites with the lowest mean flux recorded in the taylor valley 2 9 kg m 1 day 1 and the highest in the eastern victoria valley 2271 kg m 1 day 1 for 24 hours of continuous saltation the percentage of time saltation active at these locations annually is 2 4 and 13 respectively for the victoria taylor and wright valleys

bayesian geoacoustic inversion of single hydrophone light bulb data using warping dispersion analysis this paper presents geoacoustic inversion of a light bulb implosion recorded during the shallow water 2006 experiment the source is low frequency and impulsive the environment is shallow water and the acoustic signal is recorded using a single receiver in this context propagation is described by modal theory and inversion is carried out by matching modal dispersion curves in the time frequency domain experimental dispersion curves are estimated using an advanced signal processing method called warping allowing inversion to be carried out at a relatively short range 7 km moreover the inversion itself is performed using bayesian methodology this allows inference of the seabed structure from the data including the number of seabed layers resolved optimal estimates of the seabed parameters and quantitative uncertainty estimates inversion results of the experimental data are in good agreement with both ground truth and estimates from other experimental data in the same region

experimental investigation of mass flux and transport rate of different size particles in mixed sand transport by wind abstract sand transport by wind in arid regions is a geomorphic process affected by the grain size distribution knowledge of the transport behavior of each size group in mixed sand transport is important for understanding the saltation dynamics in dune migration this paper focuses on the characteristics of mass flux mass concentration horizontal velocity and transport rate of different particle size groups and the relation to their mass proportion in air experiments were carried out to analyze these relations in a wind tunnel by particle tracking velocimetry the mass flux of different size particles usually decays exponentially with height for larger size groups and deviates from exponential decay for smaller size groups the trend of mass concentration of different size groups with height is similar to the mass flux the mean horizontal velocity of different size groups generally increases with increasing height and decreases with the increase of particle size at the same height with increasing height the ratio of mass flux of each size group to the total mass flux increases for the smaller size group but decreases for the larger size group and the transition diameter of particles is about 0 14 mm for the 0 16 mm sand sample and about 0 21 0 27 mm for the 0 24 mm sand sample for the smaller size group the ratio of the mass weighted average horizontal velocity of each size group to that of all particle sizes is 1 0 and the ratio of the transport rate of each size group to the total transport rate is usually larger than its mass proportion in air this is the opposite for the larger size groups the maximum deviation of mass flux proportion of each size group from its mass proportion in air is about 15 which is determined by the mass weighted average horizontal velocity of each size group

high resolution geoacoustic inversion in shallow water a joint time and frequency domain technique high resolution geoacoustic data are required for accurate predictions of acoustic propagation and scattering in shallow water since direct measurement of geoacoustic data is difficult time consuming and expensive inversion of acoustic data is a promising alternative however the main problem encountered in geoacoustic inversion is the problem of uniqueness i e many diverse geoacoustic models can be made to fit the same data set a key and perhaps unique aspect of this approach is the combination of data analysis in both the space time and the space frequency domains this combination attempts to ameliorate the uniqueness problem by exploiting as much independent data as possible in order to meet the stringent requirements of high spatial resolution and uniqueness an entire method has been developed including a new measurement technique processing analysis technique and inversion strategy these techniques are described and then illustrated with a shallow water data set sound speed gradients in the upper few meters of the sub bottom appear to be much higher one order of magnitude than generally assumed and although often ignored a large density gradient was observed in the top layer that played an acoustically significant role

an experimental study of multiple grain size ejecta produced by collisions of saltating grains with a flat bed collision data are presented from coloured high speed films of three size fractions of sand grains saltating over a bed of the total grain population each fraction was colour tagged and the proportion of each size ejected by grains colliding with the surface was recorded on a number of films taken as the bed was progressively eroded the results confirm earlier findings that v3 v1 0 5 0 6 vn v1 08 and the rebound angle increases with decreasing grain size ejected grains are examined in relation to their size the impactor size ejection speed and angle and the number of ejecta per collision in addition changes in grain parameters are observed with time for fine impactors ejection speeds generally increase with a decrease in ejecta size but the fine fraction does not follow this trend for the coarse and medium impactors ejection angles are typically between 40 and 60 with coarse grains having shallower mean angles than fine ejecta the number of ejections per collision increases with a decrease in particle size for each impactor size the general tendency for coarse particles to be ejected at lower speeds and shallower angles than fine particles will lead to sorting of the grain sizes there is poor correlation between the forward momentum loss of the saltating grams at collision and both the forward momentum of the ejected grains and the number of ejected grains much of the forward momentum of the saltating grains is transfered to creeping grains the composition and geometry of the bed are considered to be important factors in the evolution of the saltation cloud

modeling ocean bottom reflection loss measurements with the plane wave reflection coefficient ocean bottom reflection loss has been measured at an abyssal plain site in the northeast pacific ocean the layer of unconsolidated sediment at this site is thin less than 200 m and the near surface sediments are composed of strongly reflecting sandy turbidites in consequence the surficial sediments and the relatively shallow substrate must be accounted for in describing the bottom loss measurements the bottom loss has been modeled in this paper using the plane wave reflection coefficient calculated for a geoacoustic model of the bottom developed from seismic profiling experiments carried out at the site in the model the sediment column is described by fluid layers with a relatively small value of attenuation and a large value of sound speed gradient in the surficial layer and the substrate is assumed to be a solid the bottom loss measurements are presented in 1 3 octave bands at 40 80 and 160 hz the results are well modeled at small grazing angles 20 where the interaction is confined to the surficial sediments at larger grazing angles the importance of including a solid substrate is demonstrated

grain size characteristics of sediment transported during dust storms abstract the grain size characteristics of sediment transported by wind in creep saltation and suspension during 15 dust storms in the slims river valley yukon territory were investigated grain size analysis of the transported sediment indicated that the suspended sediment is significantly finer and better sorted than the sediment transported in either surface creep or saltation the data also show that during dust storms the mean particle size of the suspended sediment decreases as a power function of height the grain size distributions of the sediment transported in suspension and surface creep are characterized by strong positive skewness which results from the selective removal of surface particles small enough to be transported by the wind at a given velocity in contrast the grai size distribution of the saltation samples are negatively skewed which is thought to result from the selective removal of the finer particles into suspension from those particles initially lifted from the surface into the air stream thus the proportion of sediment initially entrained into the air stream which returns to the surface in saltation will lack the fine grains removed in suspension and will therefore tend to be less positively or negatively skewed

changes in grain size of sand in transport over a foredune suspended sand is sampled at several heights and positions on a beach and foredune providing detailed insight into the vertical and horizontal variation in sand content in the air during landward transport grain size analysis is used to study the changes in grain size distribution during landward transport mean grain size and sorting decrease during transport changes in textural parameters follow a gradual and regular path when the sediment is transported into the foredune sediment trapped on the seaward slope at a height of 30 50 cm above the surface closely resembles the sediment trapped landward which implies that changes in the direction of transport are related to vertical changes within the sediment transport profiles the movement of sand over the vegetated foredunes is induced by turbulent forces created by the air flowing across the vegetation and the foredune leading to a change from saltation on the beach to modified saltation and suspension on the foredune small grains are lifted higher and fall more slowly than coarse grains and therefore are transported further landward resulting in a gradual decrease in grain size of the landward deposited sediment

seabed characterization on the new jersey middle and outer shelf correlatability and spatial variability of seafloor sediment properties abstract nearly 100 collocated grab samples and in situ 65 khz acoustic measurements were collected on the new jersey middle and outer shelf within an area that had previously been mapped with multibeam backscatter and bathymetry data and more recently with chirp seismic reflection profiling eighteen short cores were also collected and probed for resistivity based porosity measurements the combined data set provides a basis for empirically exploring the relationship among the remotely sensed data such as backscatter and reflection coefficients and directly measured seabed properties such as grain size distribution velocity attenuation and porosity we also investigate the spatial variability of these properties through semi variogram analysis to facilitate acoustic modeling of natural environmental variability grain size distributions on the new jersey shelf are commonly multi modal leading us to separately characterize coarse 4 mm fine

comparison of simulated and observed continental tropical anvil clouds and their radiative heating profiles abstractvertically pointing millimeter wavelength radar observations of anvil clouds extending from mesoscale convective systems mcss that pass over an atmospheric radiation measurement program arm field site in niamey niger are compared to anvil structures generated by the weather research and forecasting wrf mesoscale model using six different microphysical schemes the radar data provide the statistical distribution of the radar reflectivity values as a function of height and anvil thickness these statistics are compared to the statistics of the modeled anvil cloud reflectivity at all altitudes requiring the model to be statistically accurate at all altitudes is a stringent test of the model performance the typical vertical profile of radiative heating in the anvil clouds is computed from the radar observations variability of anvil structures from the different microphysical schemes provides an estimate of the inherent uncertainty in anvil radiative heating profiles all schemes underestima

ice microphysical properties near the tops of deep convective cores implied by the gpm dual frequency radar observations abstractusing three years of observations from the dual frequency precipitation radar dpr aboard the global precipitation measurement gpm core observatory properties of the cores of deep conve

global variability of mesoscale convective system anvil structure from a train satellite data abstract mesoscale convective systems mcss in the tropics produce extensive anvil clouds which significantly affect the transfer of radiation this study develops an objective method to identify mcss and their anvils by combining data from three a train satellite instruments moderate resolution imaging spectroradiometer modis for cloud top size and coldness advanced microwave scanning radiometer for earth observing system amsr e for rain area size and intensity and cloudsat for horizontal and vertical dimensions of anvils the authors distinguish three types of mcss small and large separated mcss and connected mcss the latter are mcss sharing a contiguous rain area mapping of the objectively identified mcss shows patterns of mcss that are consistent with previous studies of tropical convection with separated mcss dominant over africa and the amazon regions and connected mcss favored over the warm pool of the indian and west pacific oceans by separating the anvil from the raining regions of

convective initiation near the andes in subtropical south america abstractsatellite radar and radiometer data indicate that subtropical south america has some of the deepest and most extreme convective storms on earth this study uses the full 15 yr trmm precipitation radar dataset in conjunction with high resolution simulations from the weather research and forecasting model to better understand the physical factors that control the climatology of high impact weather in subtropical south america the occurrence of intense storms with an extreme horizontal dimension is generally associated with lee cyclogenesis and a strengthening south american low level jet sallj in the la plata basin the orography of the andes is critical and model sensitivity calculations removing and or reducing various topographic features indicate the orographic control on the initiation of convection and its upscale growth into mesoscale convective systems mcss reduced andes experiments show more widespread convective initiation weaker average storm intensity and more rapid propagation

leading and trailing anvil clouds of west african squall lines the anvil clouds of tropical squall line systems over west africa have been examined using cloud radar data and divided into those that appear ahead of the leading convective line and those on the trailing side of the system the leading anvils are generally higher in altitude than the trailing anvil likely because the hydrometeors in the leading anvil are directly connected to the convective updraft while the trailing anvil generally extends out of the lower topped stratiform precipitation region when the anvils are subdivided into thick medium and thin portions the thick leading anvil is seen to have systematically higher reflectivity than the thick trailing anvil suggesting that the leading anvil contains numerous larger ice particles owing to its direct connection to the convective region as the leading anvil ages and thins it retains its top the leading anvil appears to add hydrometeors at the highest altitudes while the trailing anvil is able to moisten a deep layer of the atmosphere

seabed characteristics from ambient noise at three shallow water sites in northern indian ocean ambient noise measurements at three sites along the indian continental shelf with different water column and seabed are analyzed to derive vertical directionality and further estimation of seabed characteristics directionality pattern is interpreted using features in the sound speed profiles in terms of noise notch surface duct surface bottom reflections direct arrivals and high bottom loss arrivals reflection loss estimated from the field directionality is seen to be the same for a particular site and gives an estimate of the sea bottom seabed characteristics such as critical angle and reflection coefficient from field directionality correlate well with theoretical estimation using ground truths

aeolian microtextures in silica spheres induced in a wind tunnel experiment comparison with aeolian quartz abstract microtextures in quartz attributed to aeolian transport principally bulbous edges and abrasion fatigue have seldom been tested in the laboratory under controlled conditions a wind tunnel experiment was conducted using glass spheres 70 sio 2 as a proxy for quartz with the objective of determining the extent of mechanical damage to silica glass transported in a mixture with quartz beach sand the microspheres were microscopically imaged prior to transport in a wind tunnel subjected at velocities ranging from 4 to 13 m s in sequential runs of 10 min the range in velocity is capable of lifting grains into the air column or saltating quartz grains and silica glass spheres to produce mechanical impact i e abrasion commonly experienced in aeolian transport with increasing velocity silica glass spheres which displayed minor imperfections prior to transport began to show significant grain damage exhibiting increasing depth into the silica glass fabric a result of mechanical contact as well as increasing frequency of craters dislodged plates and abrasion fatigue while pits appear earlier in the experiment 8 m s dislodged plates and abrasion fatigue need a threshold velocity of near 10 m s to become more frequent bulbous edges on the grain surface often considered the hallmark of aeolian transport are not seen in the grain population analyzed possibly because of the initial near perfect sphericity of the silica glass spheres the experiment proved that aeolian transport throughout short distances and during a relatively short period of time is enough to imprint significant abrasion marks in microspheres in fact the microtextures produced were fresh surfaces fractures and abrasion that imprinted areas of different sizes a comparison of microtextural imprints on silica glass spheres relative to coastal dune sands was made to better understand energy thresholds required to achieve grain damage

tropical intraseasonal variability in version 3 of the gfdl atmosphere model abstracttropical intraseasonal variability is examined in version 3 of the geophysical fluid dynamics laboratory atmosphere model am3 in contrast to its predecessor am2 am3 uses a new treatment of deep and shallow cumulus convection and mesoscale clouds the am3 cumulus parameterization is a mass flux based scheme but also unlike that in am2 incorporates subgrid scale vertical velocities these play a key role in cumulus microphysical processes the am3 convection scheme allows multiphase water substance produced in deep cumuli to be transported directly into mesoscale clouds which strongly influence large scale moisture and radiation fields the authors examine four am3 simulations using a control model and three versions with different modifications to the deep convection scheme in the control am3 using a convective closure based on cape relaxation both mjo and kelvin waves are weak relative to those in observations by modifying the convective closure and trigger assumptions to inhibit deep c

observations of the r reflector and sediment interface reflection at the shallow water 06 central site acoustic bottom interacting measurements from the shallow water 06 experiment experiment frequency range 1 20khz are presented these are co located with coring and stratigraphic studies showing a thin 20cm higher sound speed layer overlaying a thicker 20m lower sound speed layer ending at a high impedance reflector r reflector reflections from the r reflector and analysis of the bottom reflection coefficient magnitude for the upper two sediment layers confirm both these features geoacoustic parameters are estimated dispersion effects addressed and forward modeling using the parabolic wave equation undertaken the reflection coefficient measurements suggest a nonlinear attenuation law for the thin layer of sandy sediments

short range travel time geoacoustic inversion with vertical line array this paper presents travel time geoacoustic inversion of broadband data collected on a vertical line array at short range of 230 m during the shallow water 2006 experiments a ray tracing method combined with a hybrid optimization algorithm that utilizes differential evolution and downhill simplex was used for the inversion of sediment properties the ocean sound speed profile and geometric parameters were inverted prior to the sea bottom properties to account for the temporally variable ocean environment the sediment sound speed and thickness estimates are consistent with in situ measurements and matched field inversion results of longer range data from the experiment

regional seasonal and diurnal variations of extreme convection in the south asian region abstract temporal and spatial variations of convection in south asia are analyzed using eight years of tropical rainfall measuring mission trmm precipitation radar pr data and ncep reanalysis fields to identify the most extreme convective features three types of radar echo structures are defined deep convective cores contiguous 3d convective echo 40 dbz extending 10 km in height represent the most vertically penetrative convection wide convective cores contiguous convective 40 dbz echo over a horizontal area 1000 km2 indicate wide regions of intense multicellular convection and broad stratiform regions stratiform echo contiguous over an area 50 000 km2 mark the mesoscale convective systems that have developed the most robust stratiform regions the preferred locations of deep convective cores change markedly from india s east coast in the premonsoon to the western himalayan foothills in the monsoon they form preferentially in the evening and over land as near surface moist flow is cap

late quaternary sedimentation off new jersey new results using 3 d seismic profiles and cores abstract regional seismic reflection surveys have delineated a wedge of late quaternary sediment extending 150 km south from the hudson apron along the edge of the continental shelf off new jersey the bottom of the sediment wedge is defined by a prominent reflector r assumed to represent an erosional surface carved during a low stand of sea level probably corresponding to the wisconsinan maximum glaciation a 3 d reflection survey of a 5 0 5 km area of the southern part of the wedge was carried out in october 1989 line spacing was 10 m and shot spacing 2 5 m navigation achieved position accuracies to the survey shows that the outer shelf sediment wedge has a complex internal structure unrelated to the present seafloor morphology the sedimentary sequence appears to have been formed by a series of depositional events related to glacial melting and interrupted by at least one erosional episode marked by a seismic surface that defines a system of meandering channels faunal studies of samples from cores indicate that the sediments were deposited at shallower depths than at present but there is no evidence for deposition in shallower water or closer proximity to land than the modern mid shelf it appears that the history of periglacial marine sedimentation which accompanied the post wisconsinan deglaciation is no less complex than its continental counterpart

evolution of the population of precipitating convective systems over the equatorial indian ocean in active phases of the madden julian oscillation three dimensional radar reflectivity fields from a dual wavelength doppler polarimetric radar s polka deployed in the equatorialindian ocean are used to evaluate the composition of the populationof convective cloud elements during active phases of the mjo rainfall in active periods was intermittent occurring in 11 episodesofabout 2 4days separated byseveralnonrainydays dataforthese 2 dayperiodswerecomposited relative to the time of maximum rainfall analysis of the s polka data shows the makeup of the convective population during the rainfall episodes four types of echo structures were analyzed statistically for the 11 rainfallepisodes shallowconvectiveechoes sce deepconvectivecores dcc wideconvectiveechocores wcc and broad stratiform bsr echo regions sce and dcc events were most frequent before the maximum rainfall with the peak frequency of sce leading that of dccs wccs were most frequent during therainfallmaximum and bsr regionswere most frequentinthe later part oftherainfallepisode composited ecmwf interim re analysis era interim data and 3 hourly atmospheric soundings indicate that the 2 4 day episodes were related to the passage of equatorial waves in the early part of a rainfall episode the wave passageconditionswereunstable favoringdeeppenetratingconvectiveelements whileinthelaterperiod the wave divergence profile was commensurate with convective systems in late anvil producing stages these results support the stretched building block notion of the life cycle of tropical convection and confirm satellitebased interpretations of sce dcc wcc and bsr statistics in the composition of the convective population

spectral characteristics of tropical anvils obtained by combining trmm precipitation radar with visible and infrared scanner data the spectral characteristics of anvils in tropical areas 25 s 25 n have been investigated on the basis of data from the tropical rainfall measuring mission s trmm precipitation radar pr and a visible and infrared scanner virs from 1998 to 2007 the anvils vertical structures were captured by trmm pr and categorized into two subtypes ice anvils with an echo base of 6 km and mixed anvils with an echo base between 3 and 6 km visible and infrared signals for the anvils which are from reflectance at 0 63 and 1 6 m hereafter referred to as rf1 and rf2 respectively and the equivalent brightness temperatures of a black body at 3 7 10 8 and 12 0 m hereafter referred to as tb3 tb4 and tb5 respectively were derived simultaneously by use of trmm virs the findings reveal that the normalized frequency distribution i e probability density functions pdf of anvil tops and bases have a bimodal distribution whereas that of anvil thickness has a single peak curve for visible signals the pdf distribution of rf1 rf2 for anvils mixed anvils and ice anvils has an approximately symmetric distribution with a tropics wide averages of 0 74 072 and 0 80 0 21 0 21 and 0 20 respectively it can be concluded that ice anvils are optically thicker and contain many more ice cloud droplets at the cloud top than mixed anvils rf1 of anvils is usually lower over land than over ocean by 0 1 whereas rf2 of anvils is usually higher over land than over ocean by 0 3 this implies that anvil clouds have thinner optical depth and their cloud tops consist of many more small ice droplets over land than over ocean for infrared signals tb4 is regarded as a representative channel the pdf distribution of tb4 for anvils and mixed anvils is broad with tropics wide averages of 229 2 and 232 k respectively they contain two peaks and the secondary peak lies at a much lower value for ice anvils the pdf distribution of tb4 is a single peak curve with a tropics wide average of 219 5 k mean tb4 of anvils mixed anvils and ice anvils is usually lower over land than over ocean by 3 6 k 1 6 k and 5 k respectively in addition land ocean differences between rf1 to rf2 reflectance ratios are more obvious than those between tb4 and tb5 brightness temperatures furthermore these spectral signals have been proved to be a potentially useful way of revealing the presence of anvils over land and ocean and especially for separating anvils into the mixed and ice subtypes finally long term mean values reveal that the spectral signals of anvils and of stratiform and convective precipitating clouds are indeed different and that the difference varies with different geographical location in real time however uncertainty still exists when only spectral signals are used to discriminate anvils from stratiform and convective precipitating clouds which means active satellite observations are indispensable

spatiotemporal characteristics and large scale environments of mesoscale convective systems east of the rocky mountains abstractthe spatiotemporal variability and three dimensional structures of mesoscale convective systems mcss east of the u s rocky mountains and their large scale environments are characterized

seasonal and intraseasonal variability of mesoscale convective systems over the south asian monsoon region abstractseasonal and intraseasonal differences in mesoscale convective systems mcss over south asia are examined using a train satellites a ground based lightning network and reanalysis fields premonsoon april may mcss occur primarily over bangladesh and the eastern bay of bengal during the monsoon june september small mcss occur over the meghalaya plateau and northeast himalayan notch while large and connected mcss are most widespread over the bay of bengal monsoon mcss produce less lightning and exhibit more extensive stratiform and anvil reflectivity structures in cloudsat observations than do premonsoon mcss during the monsoon bay of bengal and meghalaya plateau mcss vary with the 30 60 day northward propagating intraseasonal oscillation while northeast himalayan notch mcss are associated with weak large scale anomalies but locally enhanced cape during intraseasonal active periods a zone of enhanced large and connected mcss precipitation and lightning extends from the northeastern a

the flux profile of a blowing sand cloud a wind tunnel investigation abstract the flux profile of a blowing sand cloud or the variation of blown sand flux with height is the reflection of blown sand particles that move in different trajectories and also the basis for checking drifting sand here we report the wind tunnel results of systematic tests of the flux profiles of different sized sands at different free stream wind velocities the results reveal that within the 60 cm near surface layer the decay of blown sand flux with height can be expressed by an exponential function q h a exp h b where q h is the blown sand transport rate at height h a and b are parameters that vary with wind velocity and sand size the significance of coefficient a and b in the function is defined a represents the transport rate in true creep and b implies the relative decay rate with height of the blown sand transport rate the true creep fraction the ratio of the sand transported on the surface h 0 to the total transport varies widely decreasing with both sand size and wind speed the flux profiles are converted to straight lines by plotting sand transport rate q h on a log scale the slope of the straight lines that represents the relative decay rate with height of sand transport rate decreases with an increase in free stream wind velocity and sand grain size implying that relatively more of the blown sand is transported to greater heights as grain size and wind speed increase the average saltating height represented by the height where 50 of the cumulative flux percentage occurs increases with both wind speed and grain size implying that saltation becomes more intense as grain size and or wind velocity increase

latent heating characteristics of the mjo computed from trmm observations the tropical rainfall measurement mission s trmm spectral latent heating algorithm shows the contributions of different forms of convection to the latent heating profiles of the madden julian oscillation over the central indian and west pacific oceans in both oceanic regions storms containing broad stratiform regions produce increased upper level heating during active madden julian oscillation mjo phases the largest differences between the central indian and west pacific ocean heating are associated with heating produced by convective elements examination of the most extreme forms of convection shows that mesoscale organized convection often produces at least as much latent heat as young vigorous deep convection heating from nonextreme often midlevel topped convection is an important component of the mjo heating in both regions in all stages of the mjo over the central indian ocean the heating profile changes from having a maximum at 2 km due to nonextreme convection to a profile during the active stage that has two maxima one at 3 km due to nonextreme convection and 6 km owing to numerous mature mesoscale storms with broad stratiform precipitation components over the west pacific the maxima at 3 and 6 km are present in all mjo stages but the magnitude of the 6 km maximum sharply increases in the active mjo stage due to an increase in the number of storms with broad stratiform precipitation areas

aeolian erosion and sand transport over the mejillones pampa in the coastal atacama desert of northern chile article i nfo the mejillones peninsula in the coastal atacama desert of northern chile is a region in which ocean atmosphere land interactions are particularly strong resulting in enhanced alongshore winds that erode the surface and transport sand particles to the sea because the aeolian particles in the laminated sediments at the bottom of mejillones bay record long term changes in the intensity of prevailing southerly winds it is fundamental to understand aeolian processes such as wind erosion and sand transport to improve paleoceanographic reconstructions the aim of the present study is to characterize the wind erosion process over the flat geomorphology of the northern portion of the mejillones peninsula the mejillones pampa including the influence of wind erosion on the initial particle size distribution and the associated fractionation processes of the mineralogical composition of moving particles through field measurements in addition we test the ability of an existing saltation model mb95 to reproduce the variability of the erosion process during the field experiment soil samples from 17 locations on this flat surface contain significant amounts of highly erodible particles with diameters in the 200 300 m and 100 150 m size ranges aeolian particles collected in bsne sand traps located at different heights near the surface exhibit a bimodal size distribution similar to that of the erodible fraction of the soils the abundance of the fine class increasing with height small stones that have a spatially variable distribution can locally reduce the intensity of wind erosion the mineralogical composition of moving particles is similar to that of the soils with quartz feldspar and calcite as the most important minerals followed by clay minerals gypsum and amphibole a value of u t is calculated for each soil particle size class subsequently the elementary contribution of each size class to the horizontal flux is calculated using white 1979 s equation and the total flux is finally obtained by integration the saltation model successfully reproduces the variability of the wind erosion process during the field experiment but over estimates the vertically integrated mass fluxes measured in situ by two orders of magnitude

mesoscale updraft magnitude and cloud ice content deduced from the ice budget of the stratiform region of a tropical cloud cluster abstract radar observations obtained during winter monex describe the three dimensional structure and development of the mesoscale stratiform region of a tropical cloud cluster the magnitudes of the mesoscale updraft and cloud ice mass content within an upper tropospheric stratiform cloud deck are deduced from a formulation of the ice budget of the stratiform region measurements of radar reflectivity at upper levels serve as the primary input data aircraft observations of ice particles are also used to guide the calculations the mesoscale updraft magnitude and cloud ice mass content are determined hourly over a period of 12 h the updraft velocities were 10 23 cm s 1 and the cloud ice contents were 0 1 0 3 g m 3 the vertical velocity estimates agree well with estimates obtained for the same cloud cluster by johnson 1982 using the kinematic method

observed structure of mesoscale convective systems and implications for large scale heating mesoscale convective cloud systems that produce large amounts of rain in mid latitudes and most of the rain in the tropics consist of a combination of convective and stratiform cloud the convective regions contain numerous deep cells that are often but not always arranged in lines the stratiform region is an outgrowth of the convective ensemble it lies adjacent to the convective region and is seeded by ice particles detrained from convective towers sometimes it lies to the rear of a propagating convective line while on other occasions it surrounds the convection the heating of the large scale environment by a mesoscale convective system is affected by both the convective and stratiform regions although processes such as melting and radiation are important the net heating by a system is dominated by condensation and evaporation associated with vertical air motions this paper reviews recent observational evidence regarding the mean vertical motion profiles in the convective and stratiform regions of mesoscale convective systems and the implications of these mean motions for the vertical distribution of heating of the large scale environment in both the convective and the stratiform regions vertical motions have been determined by various techniques including composites of rawinsonde and aircraft wind data single and dual doppler precipitation radar analyses and wind profiler observations in stratiform regions these data consistently show mean vertical velocity that is upward in the upper troposphere and downward in the lower troposphere the level separating upward from downward motion is located from 0 to 2 km above the 0 c level depending on location within the stratiform region diagnostic calculations show that these vertical motion profiles imply heating of the upper troposphere and cooling of lower levels by stratiform region processes data on vertical motions in the convective regions are less consistent from case to case these data sometimes indicate that the mean vertical velocity in convective regions is maximum in the lower troposphere in other cases the data indicate a maximum in the high troposphere diagnostic calculations show that heating profiles diagnosed from these two types of profile are quite different the first having a maximum of heating in the lower troposphere while the second has a maximum in the middle troposphere although it is difficult to determine whether or not the differences in estimates arise from different types of observations analysis methods or sampling strategies it seems likely that they stem from differences in the large scale environment of the different mesoscale systems the ubiquitous occurrence of stratiform regions in mesoscale convective systems and hurricanes together with their consistent heating profiles which systematically concentrate heating in upper levels while cooling lower levels are a major consideration in evaluating the interaction of mesoscale systems with the large scale environment however the consistency of the stratiform profiles from case to case indicates that the variability of net convective plus stratiform heating profiles from case to case lies primarily in the variation of the convective region profiles from one case to another it is suggested that future work should focus on the convective region vertical profiles of vertical motion and heating and on the large scale environmental factors that may control the variation of these profiles from case to case

anvil clouds of tropical mesoscale convective systems in monsoon regions the anvil clouds of tropical mesoscale convective systems mcss in west africa the maritime continent and the bay of bengal have been examined with trmm and cloudsat satellite data and arm ground based radar observations the anvils spreading out from the precipitating cores of mcss are subdivided into thick medium and thin portions the thick portions of anvils show distinct differences from one climatological regime to another in their upper portions the thick anvils of west africa mcss have a broad flat histogram of reflectivity and a maximum of reflectivity in their lower portions the reflectivity histogram of the bay of bengal thick anvils has a sharply peaked distribution of reflectivity at all altitudes with modal values that increase monotonically downward the reflectivity histogram of the maritime continent thick anvils is intermediate between that of the west africa and bay of bengal anvils consistent with the fact this region comprises a mix of land and ocean influences it is suggested that the difference between the statistics of the continental and oceanic anvils is related to some combination of two factors 1 the west african anvils tend to be closely tied to the convective regions of mcss while the oceanic anvils are more likely to be extending outward from large stratiform precipitation areas of mcss and 2 the west african mcss result from greater buoyancy so that the convective cells are more likely to produce graupel particles and detrain them into anvils copyright 2009 royal meteorological society

mesoscale organization and cloud microphysics in a bay of bengal depression abstract airborne radar and cloud microphysical data were obtained throughout a monsoon depression observed over the bay of bengal on 3 8 july 1979 during the summer monsoon experiment of the global atmospheric research programme the precipitation in the disturbance occurred in mesoscale rain areas 100 300 km in horizontal dimension with the largest areas tending to be elongated in the east west or northwest southeast direction these mesoscale precipitation features resembled the rain areas of equatorial cloud clusters each mesoscale precipitation feature contained intense convective cells but the area covered by rain was predominantly stratiform the convective cells in the mesoscale features were sometimes arranged in rapidly moving rather narrow arc shaped east west lines with the stratiform precipitation trailing the line in other cases the convective cells were more randomly embedded in the stratiform rain ice particle images obtained at flight level temperatures of 5 to 25 c indicated the

where is the level of neutral buoyancy for deep convection 1 this study revisits an old concept in meteorology level of neutral buoyancy lnb the classic definition of lnb is derived from the parcel theory and can be estimated from the ambient sounding lnb sounding without having to observe any actual convective cloud development in reality however convection interacts with the environment in complicated ways it will eventually manage to find its own effective lnb and manifests it through detraining masses and developing anvils lnb observation this study conducts a near global survey of lnb observation for tropical deep convection using cloudsat data and makes comparison with the corresponding lnb sounding the principal findings are as follows first although lnb sounding provides a reasonable upper bound for convective development correlation between lnb sounding and lnb observation is low suggesting that ambient sounding contains limited information for accurately predicting the actual lnb second maximum mass outflow is located more than 3 km lower than lnb sounding hence from convective transport perspective lnb sounding is a significant overestimate of the destination height level of the detrained mass third lnb observation is consistently higher over land than over ocean although lnb sounding is similar between land and ocean this difference is likely related to the contrasts in convective strength and environment between land and ocean finally we estimate the bulk entrainment rates associated with the observed deep convection which can serve as an observational basis for adjusting gcm cumulus parameterization

mesoscale convective systems 1 mesoscale convective systems mcss have regions of both convective and stratiform precipitation and they develop mesoscale circulations as they mature the upward motion takes the form of a deep layer ascent drawn into the mcs in response to the latent heating and cooling in the convective region the ascending layer overturns as it rises but overall retains a coherent layer structure a middle level layer of inflow enters the stratiform region of the mcs from a direction determined by the large scale flow and descends in response to diabatic cooling at middle to low levels a middle level mesoscale convective vortex mcv develops in the stratiform region prolongs the mcs and may contribute to tropical cyclone development the propagation of an mcs may have a discrete component but may further be influenced by waves and disturbances generated both in response to the mcs and external to the mcs waves of a larger scale may affect the propagation velocity by phase locking with the mcs in a cooperative mode the horizontal scale of an mcs may be limited either by a balance between the formation rate of convective precipitation and dissipation of stratiform precipitation or by the rossby radius of the mcv the vertical redistribution of momentum by an mcs depends on the size of the stratiform region while the net vertical profile of heating of the large scale environment depends on the amount of stratiform rain regional variability of the stratiform rain from mcss affects the large scale circulation s response to mcs heating

a cloudsat cloud object partitioning technique and assessment and integration of deep convective anvil sensitivities to sea surface temperature a cloud object partitioning algorithm is developed to provide a widely useful database of deep convective clouds it takes contiguous cloudsat cloudy regions and identifies various length scales of clouds from a tropical oceanic subset of data the methodology identifies a level above which anvil characteristics become important by analyzing the cloud object shape below this level in what is termed the pedestal region convective cores are identified based on reflectivity maxima identifying these regions allows for the assessment of length scales of the anvil and pedestal of deep convective clouds cloud objects are also appended with certain environmental quantities from european centre for medium range weather forecasts simple geospatial and temporal assessments show that the cloud object technique agrees with standard observations of local frequency of deep convective cloudiness deep convective clouds over tropical oceans play important roles in earth s climate system the newly developed data set is used to evaluate the response of tropical deep convective clouds to sea surface temperature sst several previously proposed responses are examined the fixed anvil temperature hypothesis the iris hypothesis and the thermostat hypothesis when the data are analyzed per cloud object increasing sst is found to be associated with increased anvil thickness decreased anvil width and cooler cloud top temperatures implications for the corresponding hypotheses are discussed a new response suggesting that the base temperature of deep convective anvils remains approximately constant with increasing ssts is introduced these cloud dependencies on sst are integrated to form a more comprehensive theory for deep convective anvil responses to sst

recent and modern marine erosion on the new jersey outer shelf abstract recent chirp seismic reflection data combined with multibeam bathymetry backscatter and analysis of grab samples and short cores provide evidence of significant recent erosion on the outer new jersey shelf the timing of erosion is constrained by two factors 1 truncation at the seafloor of what is interpreted to be the transgressive ravinement surface at the base of the surficial sand sheet and 2 truncation of apparently moribund sand ridges along erosional swales oriented parallel to the primary direction of modern bottom flow and oblique to the strike of the sand ridges these observations place the erosion in a marine setting post dating the passage of the shoreface ravinement and the evolution of sand ridges that form initially in the near shore environment also truncated by marine erosion are shallowly buried fluvial channel systems formed during the last glacial maximum and filled during the transgression and a regional reflector r that is 40 kyr depths of erosion range from a few meters to 10 m the seafloor within eroded areas is often marked by ribbon morphology seen primarily in the backscatter data as areas of alternating high and low backscatter elongated in the direction of primary bottom flow ribbons are more occasionally observed in the bathymetry where observed crests exhibit low backscatter and troughs exhibit high backscatter sampling reveals that the high backscatter areas of the ribbons consist of a trimodal admixture of mud sand and shell hash with a bimodal distribution of abraded and unabraded sand grains and microfauna the shell hash is interpreted to be an erosional lag while the muds and unabraded grains are in this non depositional environment evidence of recent erosion at the seafloor of previously undisturbed strata the lower backscatter areas of the ribbon morphology were found to be a well sorted medium sand unit only a few 10 s of cm thick overlying the shelly muddy sandy material concentrations of well rounded gravels and cobbles were also found in eroded areas with very high backscatter and at least one of these appears to be derived from the base of an eroded fluvial channel seafloor reworking over the transgressive evolution of the shelf appears to have switched from sand ridge evolution which is documented to 40 m water depth to more strictly erosional modification at greater water depths we suggest that this change may be related to the reduction with water depth in the effectiveness of sediment resuspension by waves resuspension is a critical factor in the grain size sorting during transport by bottom currents over large bedforms like sand ridges otherwise we speculate displacement of sand by unidirectional currents will erode the seafloor

thick anvils as viewed by the trmm precipitation radar abstract this study investigates anvils from thick nonprecipitating clouds associated with deep convection as observed in the tropics by the tropical rainfall measuring mission trmm precipitation radar pr during the 10 yr period 1998 2007 anvils observable by the pr occur on average 5 out of every 100 days within grid boxes with 2 5 resolution and with a conditional areal coverage of 1 5 unconditional areal coverage is only a few tenths of a percent anvils also had an average 17 dbz echo top of 8 5 km and an average thickness of 2 7 km anvils were usually higher and thicker over land compared to ocean and occurred most frequently over africa the maritime continent and panama anvil properties were intimately tied to the properties of the parent convection in particular anvil area and echo top heights were highly correlated to convective rain area the next best predictor for anvil areal coverage and echo tops was convective echo tops while convective reflectivities had the weakest co

seismic geomorphology of buried channel systems on the new jersey outer shelf assessing past environmental conditions abstract quantitative geomorphologic analysis of shallowly buried dendritic channel systems on the new jersey shelf provides estimates of paleo hydrologic parameters needed to link channel morphology to the former hydrodynamic setting these channels observed in 1 4 khz deep towed chirp seismic data formed presumably as fluvial systems when the shelf was exposed during the last glacial maximum lgm the presumed fluvial origin of these channels is supported by their incision into underlying pleistocene strata a chaotic seismic fill unit at their bases which may be indicative of non marine gravel lag and measured stream junction angles that are consistent with a riverine origin the channels would also have been subjected to estuarine tidal environments during ensuing sea level rise we employ empirically derived hydraulic equations for modern rivers and estuaries to estimate paleo discharges velocities and maximum shear stresses using the preserved and interpolated paleo channel geometries as a guide generally trunk main channels have box like symmetric cross sections with width depth ratios of 100 whereas smaller tributary channels have more v shaped asymmetric cross sections with width depth ratios of 40 70 the high width depth ratios along with low sinuosities 1 1 and slopes

a trans dimensional polynomial spline parameterization for gradient based geoacoustic inversion this paper presents a polynomial spline based parameterization for trans dimensional geoacoustic inversion the parameterization is demonstrated for both simulated and measured data and shown to be an effective method of representing sediment geoacoustic profiles dominated by gradients as typically occur for example in muddy seabeds specifically the spline parameterization is compared using the deviance information criterion dic to the standard stack of homogeneous layers parameterization for the inversion of bottom loss data measured at a muddy seabed experiment site on the malta plateau the dic is an information criterion that is well suited to trans d bayesian inversion and is introduced to geoacoustics in this paper inversion results for both parameterizations are in good agreement with measurements on a sediment core extracted at the site however the spline parameterization more accurately resolves the power law like structure of the core density profile and provides smaller overall uncertainties in geoacoustic parameters in addition the spline parameterization is found to be more parsimonious and hence preferred according to the dic the trans dimensional polynomial spline approach is general and applicable to any inverse problem for gradient based profiles work supported by onr

estimation of some aeolian saltation transport parameters a re analysis of williams data a new method for analysing observed aeolian sand transport rate profiles of the kind obtained by williams is presented the method involves a mathematical model of aeolian saltation detailed information about the saltation process can be calculated from the transport rate profile by means of this model the method is used to perform a re analysis of williams trap data among the main findings of this analysis is that the grain borne shear stress appears to be a smaller fraction of the total shear stress than assumed by bagnold owen in their theories of aeolian saltation other findings are that the probability distribution of the jump height of the grains does not depend much on the wind speed once the saltation is established and that the vertical component of the mean launch velocity decreases with the grain size it is approximately inversely proportional to the grain diameter our estimates of the landing angles indicate that estimates of the impact angles obtained from photographically recorded trajectories are too small due to biased sampling the influence of grain shape on the transport characteristics is mainly due to changes in the grains ability to jump when hitting the bed it is found that angular grains have a lower mean jump height than spherical grains

aeolian particle flux profiles and transport unsteadiness vertical profiles of aeolian sediment flux are commonly modeled as an exponential decay of particle mass transport with height above the surface data from field and wind tunnel studies provide empirical support for this parameterization although a large degree of variation in the precise shape of the vertical flux profile has been reported this paper explores the potential influence of wind unsteadiness and time varying intensity of transport on the geometry slope curvature of aeolian particle flux profiles field evidence from a complex foredune environment demonstrates that i the time series of wind and sediment particle flux are often extremely variable with periods of intense transport referred to herein as sediment flurries separated by periods of weak or no transport ii sediment flurries contribute the majority of transport in a minority of the time iii the structure of a flurry includes a ramp up phase lasting a few seconds a core phase lasting a few seconds to many tens of seconds and a ramp down phase lasting a few seconds during which the system relaxes to a background low intensity transport state and iv conditional averaging of flux profiles for flurry and nonflurry periods reveals differences between the geometry of the mean profiles and hence the transport states that produce them these results caution against the indiscriminate reliance on regression statistics derived from time averaged sediment flux profiles especially those with significant flurry and nonflurry periods when calibrating or assessing the validity of steady state models of aeolian saltation

vertical profiles of aeolian sand mass flux abstract vertical profiles of the horizontal mass flux of blown sand are investigated experimentally using a passive vertical array in a wind tunnel considering lower sampling efficiency of the sand trap in the near bed region this investigation is complemented by the measurements of the longitudinal profiles of mass flux made using a horizontal sand trap the experiments were conducted with two test sands and five different stream velocities in the upper part of the vertical profile the measured data exhibit an exponential decay distribution with a positive deviation occurring in the near bed region the measured longitudinal profiles are similar to the measured vertical profiles linking both profiles and the modes of sand transport it is possible that saltating sand grains give rise to the well known exponential decay distribution of mass flux and that creeping and reptating grains force a deviation from it a simple equation applicable for both the vertical and the longitudinal sand mass flux variations is introduced and the parameters are estimated from experimental data

multiscale variability of deep convection in relation to large scale circulation in toga coare deep convection over the indo pacific oceanic warm pool in the tropical ocean global atmosphere coupled ocean atmosphere response experiment toga coare occurred in cloud clusters which grouped together in regions favoring their occurrence these large groups of cloud clusters produced large scale regions of satellite observed cold cloud top temperature this paper investigates the manner in which the cloud clusters were organized on time and space scales ranging from the seasonal mean pattern over the whole warm pool region to the scale of individual cloud clusters and their relationship to the large scale circulation and sea surface temperature sst the dominant convective variability was associated with the intraseasonal oscillation iso a large eastward propagating ensemble of cloud clusters marked the iso s progress the meridional structure of the iso was strongly affected by the seasonal cycle with a southward shift from the northern hemisphere in october november to the southern hemisphere in january february the sst had an intraseasonal signal in lagged quadrature with the cold cloudiness and rainfall in coare the sst increased decreased during the convectively suppressed active phases of the iso enhanced low level westerly winds occurred toward the later stages of the enhanced convection periods of the iso though not always centered at the equator the strongest westerlies tended to be located between two synoptic scale cyclonic gyres which were often not symmetric about the equator in the low level wind field this asymmetry in the anomalous equatorial low level westerlies may have different implications for the oceanic response in the coupled atmosphere ocean system than those centered on the equator the cyclonic gyres contained highly concentrated deep convection and in four cases the gyres developed into tropical cyclones within the envelope marking the convectively active phase of the iso cloud clusters were frequently concentrated into westward propagating disturbances with a local periodicity of similar to 2 days these 2 day disturbances have been identified in earlier spectral studies and appear to be related to westward propagating inertio gravity waves in coare they typically contained numerous cloud clusters which underwent a distinct diurnal cycle most of the cloud clusters embedded in the 2 day disturbances moved westward though some were stationary and a few moved eastward a cloud duster tracking program identified groups of clusters lime dusters that exhibited continuity in time and space in the most convectively active period of the iso the tracking program identified almost the entire iso cloud ensemble as a long lasting trackable superconvective system this observation indicates the lack of a distinct scale separation between convection and large scale disturbances during the most intense convective periods in coare

extreme convection of the near equatorial americas africa and adjoining oceans as seen by trmm abstractthis study documents the preferred location and diurnal cycle of extreme convective storms that occur in the tropical band containing the east pacific ocean central and south america the atlantic ocean and northern africa data from the tropical rainfall measuring mission trmm precipitation radar show three types of convective stratiform structures that constitute extreme convective events deep convective cores dccs wide convective cores wccs and broad stratiform regions bsrs interim ecmwf re analysis era interim data show the associated synoptic environmental factors associated with the occurrence of extreme convective features the dcc wcc and bsr echoes are associated with early middle and late stages of convective system development respectively and the statistics and timing of their occurrence are related to topography and life cycle behavior of the convection storms containing dcc occur primarily over the sudanian savannas of africa and near the mountains in northern

remote sensing of sediment density and velocity gradients in the transition layer the geoacoustic properties of marine sediments e g bulk density and compressional velocity commonly exhibit large variations in depth near the water sediment interface this layer termed the transition layer is typically of o 10 1 100 m in thickness depth variations within the transition layer may have important implications for understanding and modeling acoustic interaction with the seabed including propagation and reverberation in addition the variations may contain significant clues about the underlying depositional or erosional processes characteristics of the transition layer can be measured directly e g coring or remotely remote measurements have the advantage of sampling without disturbing the sediment properties they also have the potential to be orders of magnitude faster and less expensive than direct methods it is shown that broadband seabed reflection data can be exploited to remotely obtain the depth dependent density and velocity profiles in the transition layer to high ac