radar echoes from lightning and their microphysical environment 1 a uhf profiler radar has detected lightning echoes which occurred preferentially in a balance layer the stratum of mean zero doppler velocity with rising small ice particles and falling graupel and hail thus providing the conditions for collisional charging and lightning the results support prior findings of the role of the balance layer in lightning generation the 32 8 cm profiler radar is particularly well suited for these observations because the lightning echoes are not masked by the precipitation echoes thus allowing simultaneous measurement of the microphysical and kinematic properties

painting a picture of gas hydrate distribution with thermal images 1 a study of cold thermal anomalies identified in continuous down core records of thermal structure acquired by an infrared ir camera during ocean drilling program odp leg 204 to southern hydrate ridge is combined with core based observations of structure and lithology to present new insights into the influence of lithology on hydrate distribution in an accretionary margin hydrate distribution is spatially associated with 0 5 cm thick laterally discontinuous sand horizons that compose 1 of the sedimentary section at all sites proximity to the fractured ridge crest determines the extent to which individual sand horizons host hydrate with 70 of the horizons hosting hydrate at the crest and only 29 in the basin this trend is consistent with focused up dip migration of fluids along permeable lithologic conduits and shows that lateral flow may be as important as vertical diffusion and fracture flow in determining gas hydrate distribution at hydrate ridge

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

post subduction margin structures along boyd strait antarctic peninsula abstract the pacific margin of the antarctic peninsula to the southwest of the hero fracture zone hfz is a former subducting margin which became inactive following the arrival of ridge crest segments of the antarctic phoenix ridge at the margin during the tertiary in contrast the part of the margin to the northeast of the hfz remains active tertiary convergence was approximately perpendicular to the margin and ongoing motion is thought to have the same orientation a new seismic reflection profile running along boyd strait just northeast of the landward projection of the hfz shows major structural components similar to those typically observed along the margin to the southwest of the hfz in order of increasing proximity to the margin these components are the inner shelf the shelf basin the mid shelf basement high msbh and the outer shelf the continuation of the post subduction margin structures to the active margin suggests that the boundary between crust with passive and active margins characteristics is not sharply defined our postulated scenario for tectonic evolution along boyd strait is that 1 before the arrival of the last ridge crest segment to the southwest of the hfz the inner shelf and the shelf basin were part of a cretaceous tertiary arc and forearc area 2 after the arrival thermal effects resulting from interaction of the ridge crest with the margin just southwest of the hfz lead to the formation of the msbh to the northeast but msbh uplift in boyd strait did not prevent concurrent cross shelf sediment transport contributing to development of an extensive outer shelf on the seaward flank of the msbh 3 recent extension in bransfield strait a marginal basin to the northeast of the landward projection of the hfz has caused about 10 km of seaward deflection in the strike of the part of the msbh to the northeast of the projection of the hfz

brunt vaisala frequency and rossby radii in the south atlantic abstract brunt vaisala frequency profiles have been calculated in the south atlantic and neighboring regions on a 5 5 grid between 30 n and 70 s 70 w and 70 e using the annual mean temperature and salinity profiles computed by levitus from data available from the national oceanographic data center nodc these brunt vaisala frequency profiles are used in the computation of the first and second internal rossby deformation radii the external rossby radius is computed for reference these results compare very well with those of emery et at for the equatorial atlantic very small values of the radii are evidenced in the extreme south less than 10 km in the antarctic circumpolar current for the first internal mode high vertical variability in brunt vaisala frequency profiles is also observed at the center of the subtropical gyre this behavior is probably due to the lack of deep data in this region

the vertical profile of radar reflectivity of convective cells a strong indicator of storm intensity and lightning probability abstract reflectivity data from doppler radars are used to construct vertical profiles of radar reflectivity vprr of convective cells in mesoscale convective systems mcss in three different environmental regimes the national center for atmospheric research cp 3 and cp 4 radars are used to calculate median vprr for mcss in the oklahoma kansas preliminary regional experiment for storm central in 1985 the national oceanic and atmospheric administration tropical ocean global atmosphere radar in darwin australia is used to calculate vprr for mcss observed both in oceanic monsoon regimes and in continental break period regimes during the wet seasons of 1987 88 and 1988 89 the midlatitude and tropical continental vprrs both exhibit maximum reflectivity somewhat above the surface and have a gradual decrease in reflectivity with height above the freezing level in sharp contrast the tropical oceanic profile has a maximum reflectivity at the lowest level and a very rapid decrease in reflectivity with he

migration and venting of deep gases into the ocean through hydrate choked chimneys offshore korea it has recently been recognized that in addition to low concentrations of widespread natural gas hydrate associated with bottomsimulating seismic refl ectors highly concentrated hydrate can occur in local seafl oor fl uid venting structures such structures extend upward into the regional gas hydrate stability fi eld and sometimes allow gases to escape into the overlying ocean these hydrate choked chimneys are especially prospective as an energy resource because they contain high hydrate concentrations furthermore they may be one of the most important conduits into the ocean atmosphere system for deep methane we present an analysis of two dimensional seismic refl ection data from offshore korea that give a complete picture of gas migrating from a deep source zone to feed hydrate choked vent structures at the seafl oor the gases migrate upward through networks of fractures imaged as steep amplitude striations in both diffuse and concentrated distributions we present an example of a high fl ux gas vent fed through fracture swarms emanating from a 10 15 km wide catchment zone of source gases residing 3 4 km below the seabed the geological context and the inferred distribution of hydrate within this feature are consistent with recent models in which seabed gas venting is a consequence of elevated pore fl uid salinities that are produced by a high fl ux of gases migrating independently of the pore water in contrast a nearby vent that is not plumbed into the same high fl ux system appears to be dominated more by gas rich liquids we present these two vent structures as type cases for high and lowfl ux fl uid escape systems in the seabed furthermore we suggest that since the amount of gas trapped as hydrate within the vents is small compared with the amount in the underlying reservoir the greatest risk for increased methane input to the atmosphere associated with climate driven oceanic warming is not the melting of hydrate but an increase in the number of deep reservoirs able to vent gases through the seabed that occurs as the regional gas hydrate stability zone thins

evolution structure cloud microphysical and surface rainfall processes of monsoon convection during the south china sea monsoon experiment abstract a two dimensional cloud resolving simulation is combined with dual doppler and polarimetric radar analysis to study the evolution dynamic structure cloud microphysics and rainfall processes of monsoon convection observed during the south china sea scs summer monsoon onset overall the model simulations show many similarities to the radar observations the rainband associated with the convection remains at a very stable position throughout its life cycle in the northern scs the reflectivity pattern exhibits a straight upward structure with little tilt the positions of the convective transition and stratiform regions produced by the model are consistent with the observations the major difference from the observations is that the model tends to overestimate the magnitude of updraft as a result the maximum reflectivity generated by the model appears at an elevated altitude the surface rainfall processes and associated thermodynamic dynamic and cloud microphysical processes are examine

effects of ridge crest trench interaction on antarctic phoenix spreading forces on a young subducting plate precise measurements of spreading rates on marine magnetic profiles collected to the west of the antarctic peninsula have enabled some consideration of the forces governing plate motion since antarctic phoenix motion has been controlled by the local rather than global force balance over the last 35 m y the total effective driving force per unit length of trench is calculated to have ranged between 2 6 and 3 6 1012 n m which is much less than is commonly thought necessary to support subduction conventional calculations may overestimate slab pull for old slabs because they neglect the effect of extensional disruption in limiting the contribution to the balance of forces at the trench the low estimate of driving forces obtained here implies that resistive forces are also smaller than is generally assumed driving forces show a strong correlation with observed spreading rates which indicates that resistive forces were largely velocity dependent fluid migration up the subduction zone may elevate temperatures in and around the shear zone reducing resistive forces below the levels required by purely conductive models changes in convergence rate may affect the depths of both the brittle ductile deformation boundary and the basalt eclogite phase change causing a negative feedback which would appear as a velocity dependent resistive force the different driving forces acting on the ne and sw parts of the phoenix plate as a consequence of older oceanic lithosphere at the trench in the ne caused antarctic phoenix spreading to take place about a near pole to the sw since 21 m y ago and ultimately resulted in disruption of the phoenix plate about 9 m y ago spreading rates decreased abruptly about 6 m y ago probably because of e w compression across the long transform faults bounding the phoenix plate however spreading on the last three segments of the antarctic phoenix ridge continued at least until 4 m y ago either spreading stopped progressively from sw to ne or the final stage took place about a very near pole to the sw a magnetic quiet zone extends up to 95 km from the margin between the tula fracture zone and the north anvers fracture zone and is thought to indicate that the ridge crest became buried by terrigenous sediment prior to collision the absence of a magnetic quiet zone associated with the most recent ridge crest trench collisions suggests a change in sedimentary regime during the late miocene anomalously fast apparent spreading rates between 23 and 21 m y ago are thought to indicate an error in this part of the magnetic reversal time scale

permeability evolution during the formation of gas hydrates in marine sediments 1 fluxes of gas energy and fluid water with dissolved gas are known to control the distribution of gas hydrate and free gas in gas hydrate reservoirs but theoretical studies have so far not focused on the effect of sediment properties e g permeability on these fluxes during the formation of gas hydrate deposits using a transient one dimensional two phase gas hydrate and fluid numerical model based on a coupled conservation approach we examine permeability clogging during gas hydrate formation in end member porous media and fractures initially lacking hydrate and determine the resulting changes in fluid and advective energy flux gas hydrate accumulates most rapidly at depth in both systems a result consistent with borehole logging and seismic studies on the blake ridge consideration of the ratio of surface area to fluid volume explains model results that imply more rapid permeability reduction in the porous media system and more uniform hydrate formation as a function of depth in the fracture system depending on fluid flux fracture aperture or pore sizes and other factors the timescale for permeability clogging due to the accumulation of gas hydrate ranges from thousands to millions of years regenerating gas hydrate to a concentration of 10 15 of pore space in marine settings with fluid fluxes characteristic of hydrate ridge or blake ridge requires 103 105 years meaning that hydrate deposits in these settings cannot be viewed as a naturally renewable resource these results also imply that significant time is required to reestablish gas hydrate deposits after large scale dissociation events associated with global scale climate change

the vertical structure of toga coare convection part i radar echo distributions radar data collected by the 5 cm mit radar which was deployed aboard the r v vickers during the intensive observing period of the tropical ocean global atmosphere coupled ocean atmosphere response experiment are partitioned into convective and stratiform cartesian grid columns the vertical structure of convective echo is examined through the use of two variables echo top height and the height of the 30 dbz reflectivity contour the first of these variables has traditionally been used to describe the vertical structure characteristics of convection and the second has recently been linked to internal microphysical properties and lightning histograms of the relative frequency of convective only echo top heights and 30 dbz contour heights were constructed for the three cruises of the vickers with each cruise experiencing different phases of the intraseasonal oscillation iso cruise 1 which was dominated by the convectively inactive phase of the iso was characterized by the highest frequency of shallow convection based on echo top heights whereas cruise 2 which was dominated by a particularly well defined passage of the convective phase of the iso exhibited the tallest echo top heights cruise 3 convection was influenced by moderate westerly surface winds characteristic of postwesterly wind burst conditions and convection was of intermediate height when viewed as a function of internal vertical structure i e 30 db z contour height the frequency distributions vary less from cruise to cruise with cruises 1 and 2 having nearly identical distributions of convective 30 dbz contour heights furthermore when the contribution to convective rainfall is examined as a function of 30 dbz contour height it is seen that relatively more rain fell from vertically intense convection i e convection with tall 30 dbz contours during cruises 1 and 3 than during cruise 2 instantaneous correlations between rainfall rate and radar echo height were highly scattered about a mean value of about 0 55 whereas rainfall rate and 30 dbz contour height correlations peaked at about 0 8 and exhibited much less scatter

southern acc front to the northeast of south georgia pathways characteristics and fluxes 1 in december 2000 we conducted high resolution hydrographic and towed undulator transects across the south georgia shelf and into the deep waters of the georgia basin the southern antarctic circumpolar current front saccf was observed flowing northwestward close to the base of the slope at 53 7 s with a second manifestation around 53 4 s having flow in the reverse direction both crossings had a significant barotropic component aligned with the flow the region of the saccf was characterized by large scale undulations of properties on horizontal scales of 5 10 km similar to the local internal rossby radius we observe a distinct surface temperature gradient associated with the saccf in the vicinity of south georgia and demonstrate the usefulness of this by tracing the course of the front around the island with advanced very high resolution radiometer data a distinct northward deflection of the front to the north of south georgia is probably due to topographic steering by the north georgia rise the signature of the saccf is pronounced in the circumpolar deep water with strong isopycnal interleaving indicative of cross frontal mixing the salinity of the weddell sea deep water is marginally higher between the two manifestations of the saccf reflecting the different pathways from its source regions in the weddell sea remarkably strong vertical gradients of potential temperature and salinity exist in the bottom 100 m of the water column at depths of around 3500 m because of the vertical juxtaposition of waters that have taken different routes around the northeast georgia rise

investigation of microphysical processes occurring in isolated convection during name abstracta major objective of the north american monsoon experiment name was to quantify microphysical processes within convection occurring near the steep topography of northwestern mexico a previous study compared examples of isolated convection using polarimetric radar data and noted a dependence on mixed phase processes via drop freezing and subsequent riming growth along the coastal plain and western slopes with an even greater role of melting ice in rainfall production over the highest terrain despite the higher frequency of these isolated cells compared to organized convective systems the latter were responsible for 75 of rainfall therefore this study seeks to evaluate the role of mesoscale organization on microphysical processes and describes the evolution of these systems as a function of topography similar to isolated convection both warm rain and ice based processes played important roles in producing intense rainfall in organized convection although similarities existed between cell

characterization of excess pore pressures at the toe of the nankai accretionary complex ocean drilling program sites 1173 1174 and 808 results of one dimensional modeling 1 elevated fluid pore pressures play a critical role in the development of accretionary complexes including the development of the decollement zone in this study we used measured permeabilities of core samples from ocean drilling program odp leg 190 to develop a permeability porosity relationship for hemipelagic sediments at the toe of the nankai accretionary complex this permeability porosity relationship was used in a one dimensional loading and fluid flow model to simulate excess pore pressures and porosities simulated excess pore pressure ratios as a fraction of lithostatic pressure hydrostatic pressure using the best fit permeability porosity relationship were lower than predicted from previous studies we then tested sensitivity of excess pore pressure ratios in the underthrust sediments to bulk permeability lateral stress in the prism and a hypothetical low permeability barrier at the decollement our results demonstrated significant increase in pore pressures below the decollement with lower bulk permeability such as obtained by using the lower boundary of permeability porosity data or when a low permeability barrier is added at the decollement in contrast pore pressures in the underthrust sediments demonstrated less sensitivity to added lateral stresses in the prism although the profile of the excess pore pressure ratio is affected both simulations with lateral stress and a low permeability barrier at the decollement resulted in sharp increases in porosity at the decollement similar to that observed in measured porosities furthermore in both scenarios maximum excess pore pressure ratios were found at the decollement suggesting that either of these factors would contribute to stable sliding along the decollement

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

compressional velocity structure and poisson s ratio in marine sediments with gas hydrate and free gas by inversion of reflected and refracted seismic data south shetland islands antarctica abstract a bottom simulating reflector bsr on the south shetland margin antarctic peninsula was surveyed within the progetto nazionale di ricerche in antartide pnra high resolution multichannel mcs reflection profiles were acquired and a three component ocean bottom seismograph obs was deployed where the bsr was particularly strong the compressional velocity field associated to the bsr was determined by the inversion of travel times of reflected mcs data and refracted obs data events information on shear wave velocities was extracted from the horizontal components of the obs records the analysis indicates the presence of velocity anomalies both above and below the bsr that are not related to the lithologic characteristics of the sedimentary column but can be associated to gas hydrate and free gas presence in pore space amplitude versus offset avo analysis was performed on common depth point gathers which correspond to the obs position the study determined reflection coefficient trends that provided qualitative information about gas hydrate and free gas abundance a theoretical model for elastic porous media was applied to quantify amounts of gas hydrate and free gas the resulting theoretical velocity curves were compared to interval velocity obtained by seismic inversion a quantitative estimation of free gas and gas hydrates trapped in the sediment pore spaces was made by interpreting velocity anomalies with respect to reference velocity curves normally consolidated marine terrigenous sediments the comparison of the results obtained by these independent methods seismic inversion avo analysis and theoretical model gives consistent values of poisson s ratio and gas hydrate and free gas estimation

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

electrically active hot towers in african easterly waves prior to tropical cyclogenesis abstract it has been hypothesized that intense convective scale hot towers play a role in tropical cyclogenesis via dynamic and thermodynamic feedbacks on the larger scale circulation in this study the authors investigate the role that widespread and or intense lightning producing convection i e electrically hot towers present in african easterly waves aews may play in tropical cyclogenesis over the east atlantic ocean the 700 hpa meridional wind from the ncep ncar reanalysis dataset was analyzed to divide the waves into northerly southerly trough and ridge phases the aews were subsequently divided into waves that developed into tropical storms i e developing and those that did not develop into tropical storms i e nondeveloping finally composites were created using various ncep variables lightning data gathered with the zeus network and worldwide lightning location network wwlln and brightness temperature data extracted from the nasa global merged infrared brightness temperatur

the cenozoic subduction history of the pacific margin of the antarctic peninsula ridge crest trench interactions new magnetic anomaly identifications w of the shackleton fracture zone show 5 spreading sections separated by fracture zones in the 2 most southerly the ridge crest collided with a trench at the margin of the antarctic peninsula only 6 5 and 4 ma ago the latest of a series of collisions starting at the base of the peninsula so ma ago following each collision spreading and subduction both stopped opposite the south shetland trench and actively extending bransfield strait spreading also stopped 4 ma ago but before the spreading centre reached the trench the tendency of the subducting plate to continue sinking probably initiated the opening of the bransfield strait the parallelism between fracture zone orientation on the descending plate and convergence direction previously thought responsible for the tectonic segmentation of the peninsula was effective for only 10 30 ma before collision before that either the fracture zones did not extend to the trench or the subducting ocean floor formed at the farallon phoenix nazca aluk boundary with fracture zones oblique to the subduction direction the aleutian arc kula ridge model in which arc magmatism virtually ceases when ocean floor younger than 25 30 ma occurs beneath the arc fits the distribution of antarctic peninsula radiometric dates explaining a 50 60 ma gap between collisions and youngest ages in the s and possibly the migration of the youngest activity towards the trench thus gaps in the geologic record of arc magmatism need not imply cessation of subduction the progressive steepening of the peninsular margin towards the 4 ma collision site suggests tectonic erosion of the fore arc as the ridge crest approached

an approach to estimate gas hydrate saturation from 3 d heterogeneous resistivity model a study from krishna godavari basin eastern indian offshore abstract a method is proposed to estimate gas hydrate saturation from three dimensional 3 d heterogeneous model of resistivity simulated using resistivity log pure gas hydrates are highly resistive compared to the host sediments and their presence in the pore space of sediments increase the resistivity of the formation the anomalous increase of resistivity is used as a proxy for the delineation of gas hydrates using the resistivity log a 3 d heterogeneous resistivity model has been constructed from one dimensional resistivity log in krishna godavari kg basin eastern indian offshore the simulated model contains all small scale variation in resistivity of the reservoir and maintains all properties associated with covariance like root mean square fluctuation characteristic scales and fractal dimension of the observed log we have estimated volumetric hydrate saturation using the three dimensional simulated model the porosity used for estimating hydrate saturation is calculated from the simulated density field generated using the observed density log estimated average gas hydrate saturation is about 9 84 of the pore volume over a 1000 m 1000 m x 131 m cubic meters area

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

cloud to ground lightning observations from toga coare selected results and lightning location algorithms abstract recently observations of electrified oceanic convection and associated cloud to ground cg lightning were obtained over the tropical western pacific ocean during toga coare tropical ocean global atmosphere coupled ocean atmosphere response experiment during coare observations of convection were made using a variety of instrument platforms including ship and airborne doppler radars an advanced lightning direction finder aldf network and a shipborne inverted electric field mill this study focuses on data collected by the coare aldf network fusion of those data with observations and the methods used to calculate accurate cg return stroke locations analysis of cg lightning data and doppler radar data indicates that lightning producing oceanic convection is characterized by deep vertically developed convective cells with radar reflectivities exceeding 30 dbz above the height of the 10 c level in several cases a peak in cg frequency occurred coincident with the descent of precipitation

the development and structure of an oceanic squall line system during the south china sea monsoon experiment abstract a primary goal of the south china sea monsoon experiment scsmex a major field campaign of the tropical rainfall measuring mission trmm is to define the initiation structure evolution and dynamics of precipitation processes associated with the onset of the south china sea scs summer monsoon in this study dual doppler and dual polarimetric radar analysis techniques are used to investigate the development and structure of a squall line system observed on 24 may 1998 the focus is the linkage between the airflow and the microphysical fields through the system the squall line system including three distinct lines persisted from 1200 utc 24 may to the following day a detailed study was performed on the structure of the second and most intense line lasting for over 10 h compared to tropical squall lines observed in other regions this narrow squall line system had some interesting features including 1 maximum reflectivity as high as 55 dbz 2 relatively little stratiform rainfall th

radar observations of the kinematic microphysical and precipitation characteristics of two mcss in trmm lba 1 dual doppler and polarimetric radar observations are used to analyze two mesoscale convective systems mcss that occurred during the tropical rainfall measuring mission large scale biosphere atmosphere field campaign the mcss formed in different meteorological regimes based on profiles of atmospheric wind and thermodynamic data the first mcs event 26 january 1999 was a squall line that formed in low level easterly flow and had an intense leading line of convection in contrast the 25 february 1999 mcs formed in low level westerly flow and was best characterized by stratiform precipitation with embedded convective elements the radar analyses suggest that the mcss were distinct in terms of overall vertical structure characteristics in particular polarimetric radar cross sections indicated the presence of an active mixed phase zone in the easterly mcs that was largely absent in the westerly case the easterly mcs had considerably more precipitation ice in the middle to upper troposphere compared to the westerly mcs composite analyses showed that the easterly mcs had higher peak reflectivities and a smaller reflectivity gradient above the 08c level in convective regions of the storm compared to the westerly mcs event moreover mean profiles of both vertical air motion and vertical mass transport in the convective portion of the easterly mcs were larger over a factor of 2 at some heights below the 08 c level than those in the westerly event these observations suggest that the easterly and westerly wind regimes in the southwest amazon region produce convection with different vertical structure characteristics similar to regimes elsewhere in the global tropics e g maritime continent index terms 3314 meteorology and atmospheric dynamics convective processes 3329 meteorology and atmospheric dynamics mesoscale meteorology 3354 meteorology and atmospheric dynamics precipitation 1854 3374 meteorology and atmospheric dynamics tropical meteorology keywords microphysics tropical precipitation polarimetric radar mesoscale convective system

three dimensional kinematic and microphysical evolution of florida cumulonimbus part ii frequency distributions of vertical velocity reflectivity and differential reflectivity abstract high resolution radar data collected in florida during the convection and precipitation electrification experiment are used to elucidate the microphysical and kinematic processes occurring during the transition of a multicellular storm from convective to stratiform stages a statistical technique is employed to examine the evolving properties of the ensemble small scale variability of radar reflectivity vertical velocity and differential reflectivity over the entire storm differential radar reflectivity data indicate that the precipitation at upper levels was nearly glaciated early in the storm s lifetime dual doppler radar data show that throughout the storm s lifetime both updrafts and down drafts were present at all altitudes and that most of the volume of the radar echo contained vertical velocities incapable of supporting precipitation size particles thus the ensemble microphysical properties of the storm were increasingly dominated by particles falling in an environment of weak vertic

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

gas hydrate versus geological features the south shetland case study abstract a gas hydrate reservoir is hosted in marine sediments of an accretionary prism located offshore the south shetland islands antarctic peninsula and affected by widespread deformations to analyse gas hydrate distribution and fluid circulation inside sediments available velocity models were used seismic velocities are translated in terms of hydrate porosity which is the difference between the reference porosity i e the porosity without gas hydrate and the effective porosity i e the porosity reduced by the gas hydrate presence the pre stack depth migration sections underlined the presence of several geological features such as gentle and open folds fractures and faults in this paper we observed a relationship between syncline anticline structures and hydrate presence in particular a relationship is underlined between the hydrate porosity values and the distance from the hinge of the anticline the hydrate porosity increases toward the limbs of anticline the micro fracturing model supports the idea that the syncline favours the hydrate formation while the anticline favours the free gas accumulation below the bottom simulating reflector

comparing the convective structure and microphysics in two sahelian mesoscale convective systems radar observations and crm simulations two mesoscale convective systems mcss observed during the african monsoon multidisciplinary analyses amma experimentaresimulatedusingthethree dimensional 3d goddardcumulusensemble model this studywasundertaken todeterminethe performance ofthe cloud resolving modelin representing distinct convective and microphysical differences between the two mcss over a tropical continental location simulations are performed using 1 km horizontal grid spacing a lower limit on current embedded cloudresolving models within a global multiscale modeling framework simulated system convective structure and microphysics are compared to radar observations using contoured frequency by altitude diagrams cfads calculated ice and water mass and identified hydrometeor variables vertical distributions of ice hydrometeors indicate underestimation at the mid and upper levels partially due to the inability of the model to produce adequate system heights the abundance of high reflectivity values below and near the melting level in the simulation led to a broadening of the cfad distributions observed vertical reflectivity profiles show thathighreflectivityis presentat greaterheights thanthe simulations produced thoughtto bea resultof using a single moment microphysics scheme relative trends in the population of simulated hydrometeors are in agreement with observations though a secondary convective burst is not well represented despite these biases the radar observed differences between the two cases are noticeable in the simulations as well suggesting that the model has some skill in capturing observed differences between the two mcss

global statistics of lightning in anvil and stratiform regions over the tropics and subtropics observed by the tropical rainfall measuring mission 1 the statistics of lighting in the anvil and stratiform regions of convective systems are summarized from tropical rainfall measuring mission trmm satellite observations from 1998 to 2009 the locations of lightning flashes in convective systems are determined by combining three dimensional precipitation radar pr observations with lightning flash center locations from lightning imaging sensor observations the geographical distributions of flashes in the anvil and stratiform regions of thunderstorms over the tropics and subtropics are presented flashes in stratiform regions are found to account for 5 6 of all lightning flashes observed within the trmm pr swath while flashes in nonraining anvil regions made up another 5 5 of the sample diurnally flashes in anvil regions peak earlier than flashes in stratiform regions 15 30 lt as opposed to 17 30 lt seasonal and regional variations of these flashes are discussed features in pr observations that likely contribute to charge separation are identified as contiguous areas with 6 km echoes exceeding 30 dbz lightning flashes are then assigned to one of these features by the nearest neighbor method convective properties of features linked with lightning in stratiform and nonraining anvil regions are then analyzed we find that features associated with lightning flashes in anvil regions are relatively weak and occur in small systems composed of a single convective region while flashes in the stratiform regions are also relatively weak but more likely occur in multicell systems about 15 of features with lightning are associated with at least one stratiform or anvil flash

advection in polar and sub polar environments impacts on high latitude marine ecosystems we compare and contrast the ecological impacts of atmospheric and oceanic circulation patterns on polar and sub polar marine ecosystems circulation patterns differ strikingly between the north and south meridional circulation in the north provides connections between the sub arctic and arctic despite the presence of encircling continental landmasses whereas annular circulation patterns in the south tend to isolate antarctic surface waters from those in the north these differences influence fundamental aspects of the polar ecosystems from the amount thickness and duration of sea ice to the types of organisms and the ecology of zooplankton fish seabirds and marine mammals meridional flows in both the north pacific and the north atlantic oceans transport heat nutrients and plankton northward into the chukchi sea the barents sea and the seas off the west coast of greenland in the north atlantic the advected heat warms the waters of the southern barents sea and with advected nutrients and plankton supports immense biomasses of fish seabirds and marine mammals on the pacific side of the arctic cold waters flowing northward across the northern bering and chukchi seas during winter and spring limit the ability of boreal fish species to take advantage of high seasonal production there southward flow of cold arctic waters into sub arctic regions of the north atlantic occurs mainly through fram strait with less through the barents sea and the canadian archipelago in the pacific the transport of arctic waters and plankton southward through bering strait is minimal in the southern ocean the antarctic circumpolar current and its associated fronts are barriers to the southward dispersal of plankton and pelagic fishes from sub antarctic waters with the consequent evolution of antarctic zooplankton and fish species largely occurring in isolation from those to the north the antarctic circumpolar current also disperses biota throughout the southern ocean and as a result the biota tends to be similar within a given broad latitudinal band south of the southern boundary of the acc there is a large scale divergence that brings nutrient rich water to the surface this divergence along with more localized upwelling regions and deep vertical convection in winter generates elevated nutrient levels throughout the antarctic at the end of austral winter however such elevated nutrient levels do not support elevated phytoplankton productivity through the entire southern ocean as iron concentrations are rapidly removed to limiting levels by spring blooms in deep waters however coastal regions with the upward mixing of iron maintain greatly enhanced rates of production especially in coastal polynyas in these coastal areas elevated primary production supports large biomasses of zooplankton fish seabirds and mammals as climate warming affects these advective processes and their heat content there will likely be major changes in the distribution and abundance of polar biota in particular the biota dependent on sea ice

some characteristics of thunderstorms over bathurst and melville islands near darwin australia a study defining the occurrence structure and evolution of maritime continent island thunderstorms over bathurst and melville islands near darwin australia is presented satellite data for the november december pre monsoon transition season show unambiguous records of island thunderstorms on at least 65 of days over the period 1978 1986 storms develop most commonly between 1230lst and 1530lst and radar data indicate a mean lifetime of 2 5 h non occurrence was found on only 7 of the days examined and was associated with a return to dry flow typical of the early transition season with middle level subsidence or suppressed conditions in the wake of previous convective activity environmental sounding data indicated that these maritime continent thunderstorms develop in a regime with moderate cape low to moderate shear and high moisture the dynamic regime is characteristic of multicellular storms examination of the evolution of the storms indicates the existence of a typical lifecycle but with considerable variability in detail initially the lifecycle is consistent with the multicellular storm concept but the developing storms tend to aggregate to form one or more mesoscale systems which in turn may develop into propagating squall lines in the mature stage the developing storms have preferred geographic regions of genesis and intensification over the islands and while motion of the storms is variable it is generally consistent with the mean surface to 700mb pressure weighted flow

the 29 june 2000 supercell observed during steps part i kinematics and microphysics this is a two part study that addresses the kinematic microphysical and electrical aspects of a severe storm that occurred in western kansas on 29 june 2000 observed during the severe thunderstorm electrification and precipitation study steps field campaign in this first part polarimetric and doppler radar data are used along with a simple particle growth model to examine the evolution of the kinematic and microphysical properties of the storm from its earliest developing phase through its mature and dissipating phases during its severe stage the storm exhibited frequent positive cloud to ground lightning strikes very large 5 cm hail and a tornado doppler derived winds radar reflectivity and hydrometeor classifications from the polarimetric data over a nearly 4 h period are presented it is shown that updraft velocity and vertical vorticity had to reach magnitudes of at least 10 m s 1 and 10 2 s 1 and occupy major portions of the storm before it could produce most of the observed severe storm characteristics furthermore the establishment of cyclonic horizontal flow around the right flank of the updraft core was essential for hail production most of the largest hail grew from near millimeter sized particles that originated in the mid to upper level stagnation region that resulted from obstacle like flow of environmental air around the divergent outflow from the upper part of the updraft these recycling embryonic particles descended around the right flank of the updraft core and reentered the updraft intermingling with other smaller particles that had grown from cloud base along the main low level updraft stream

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

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

estimating pore space gas hydrate saturations from well log acoustic data relating pore space gas hydrate saturation to sonic velocity data is important for remotely estimating gas hydrate concentration in sediment in the present study sonic velocities of gas hydrate bearing sands are modeled using a three phase biot type theory in which sand gas hydrate and pore fluid form three homogeneous interwoven frameworks this theory is developed using well log compressional and shear wave velocity data from the mallik 5l 38 permafrost gas hydrate research well in canada and applied to well log data from hydrate bearing sands in the alaskan permafrost gulf of mexico and northern cascadia margin velocity based gas hydrate saturation estimates are in good agreement with nuclear magneto resonance and resistivity log estimates over the complete range of observed gas hydrate saturations

cloud to ground lightning associated with the evolution of a multicell storm 1 the relationship of cloud to ground cg lightning strikes to the stages of updraft downdraft evolution is investigated in a multicell thunderstorm that occurred on 11 july 1989 during the north dakota thunderstorm project with only single doppler radar data available for this storm reflectivity and single doppler velocity signatures are used to identify individual cells within the storm and to deduce the stage of evolution within each cell cell evolution appeared to follow the thunderstorm project model of the late 1940s updraft growth and vertical development during the growing cumulus stage updraft peaking in the upper portion of the cell and rainy downdraft descending from the middle portion during the mature stage and lighter precipitation settling out during the dissipating stage on 11 july cells tended to occur in clusters each cluster consisting of growing mature and dissipating cells close together in both time and space no cg strikes were detected when the convective region of the storm contained only one cluster of cells all strikes occurred when there were two or more clusters of cells with only two exceptions strikes occurred in the convective region of the storm typically closer to growing mature cells than to dissipating cells these observations support the hypothesis that descending precipitation creates electrical conditions conducive to flashes reaching ground however these observations also suggest that the greater complexity of electrical structure due to the juxtaposition of several cells is especially conducive to cg flashes and can cause cg flashes to occur earlier in a new cell s life cycle than would otherwise be the case

seismic character of bottom simulating reflectors examples from the mid norwegian margin three classes of bottom simulating reflectors bsr cross cut the post breakup sediments of the mid norwegian margin the first class is caused by free gas at the base of the pressure and temperature dependent gas hydrate stability zone the second class of bsr is caused by the diagenetic transition from opal a to opal ct the third class of bsr is always observed underneath the opal a opal ct transition but heat flow data and the amplitude characteristics of this arrival exclude one of the known silicate diagenetic transitions or gas hydrates as the explanation for this reflector odp site 643 drilling results from the voring plateau suggest two possible processes as the reason for this third bsr a smectite illite conversion or b a sudden increase in the abundance of authigenic carbonates the genesis of both is pressure and temperature dependent and could potentially result in a cross cutting seismic reflector the data are not conclusive as to which process is causing the third class of observed bsr

anatomy of cirrus clouds results from the emerald airborne campaigns the emerald airborne measurement campaigns have provided a view of the anatomy of cirrus clouds in both the tropics and mid latitudes these experiments have involved two aircraft that combine remote sensing and in situ measurements results are presented here from two separate flights one in frontal cirrus above adelaide australia the other in the cirrus outflow from convection above darwin recorded images of ice crystals are shown in relation to the cloud structure measured simultaneously by an airborne lidar in mid latitude frontal cirrus columnar and irregular ice crystals were observed throughout the cloud while rosettes were found only at the top the cirrus outflow from a tropical thunderstorm extended for hundreds of kilometres between the heights of 12 2 and 15 8 km this was composed mainly of hexagonal plates columns and large crystal aggregates that originated from within the main core region of the convection a small number of bullet rosettes were found at the top of the outflow cirrus and this is interpreted as an indication of in situ crystal formation it was found that the largest aggregates fell to the lower regions of the outflow cirrus cloud while the single crystals and small aggregates remained at the top

tropical island convection in the absence of significant topography part ii nowcasting storm evolution abstract this paper examines influences on the short range prediction of organized convection under conditions of strong diurnal forcing the analyses are based on data provided by the maritime continent thunderstorm experiment which was conducted in 1995 over the tiwi islands 11 s 50 100 km north of the australian continent organized convection over the tiwi islands is often dubbed hector by residents and researchers alike the authors purpose is to utilize results from these analyses to improve convective storm nowcast systems and their associated forecast and warning products the environmental near surface wind direction is shown to be singularly influential in statistically predicting the location of convection and its time of occurrence over the tiwi islands this finding is robust despite the fact that mean wind speeds were merely 1 4 m s 1 the island boundary layer water vapor mixing ratio derived from a morning sounding and inland surface stations is shown to be correlated with measu

transport and structure within the antarctic circumpolar current to the north of south georgia the antarctic circumpolar current acc crosses rugged topography to the north of south georgia in this region the subsurface expression of the polar front pf is generally thought to occur north of the maurice ewing bank meb close to the subantarctic front saf however in january 1996 the pf was south of the bank separate from the saf in a position where it was most likely constrained by local bathymetry high rates of transport 25 sv eastward were present at the pf consistent with previous estimates for this current core high transport rates 20 sv westward were also present along the northern shelf of south georgia close to where the southern acc front saccf has previously been reported during our occupation the saccf was not encountered as it probably lay outside the survey area comparisons with recent circumpolar analyses emphasise the potential for variability in the region

southern antarctic circumpolar current front to the northeast of south georgia horizontal advection of krill and its role in the ecosystem during december 2000 and january 2001 we conducted a high resolution hydrographic and bioacoustic transect rrs james clark ross cruise 57 that extended across the south georgia shelf from close to cumberland bay across the shelf break and slope and into the deep waters of the georgia basin beyond we observed a high biomass of zooplankton between 53 8degrees and 53 4degreess associated with the inshore northwestward flow of the southern antarctic circumpolar current front saccf that occurred in around 2500 m of water close to the base of the slope there was very little zooplankton biomass present in the more offshore eastward flowing waters where a second manifestation of the saccf was also present on the section the region of enhanced zooplankton biomass was over 50 km in horizontal extent with the highest densities 10 g m 3 in the area of strongest flow 35 cm s 1 the majority of the zooplankton present on the section was antarctic krill and most of it occurred in the upper 100 m the rate of physically mediated transport of antarctic krill across the off shelf sections similar to10 km of the transect showed marked variation with highest rates 10 6 g s 1 associated with the northwestward flow of the saccf farther offshore where the krill biomass and flow rates were much reduced the flux of krill was very low the integrated horizontal flux of krill across the offshore sections was large 192 x 10 3 t d 1 and to the northwest a second occupation of the transect showed that the krill flux is highly variable and we discuss the various physical and biological factors that will generate such variability we show that horizontal flux of krill in ocean currents is a major factor in determining the abundance of krill around south georgia

motion of the scotia sea plates earthquake data from the scotia arc to early 2002 are reviewed in the light of satellite gravity and other data in order to derive a model for the motion of plates in the scotia sea region events with magnitude greater than or equal to5 which occurred on or near the boundaries of the scotia and sandwich plates and for which centroid moment tensor cmt solutions are available are examined the newer data fill some of the previous sampling gaps along the boundaries of the scotia and sandwich plates and provide tighter constraints on relative motions variations in the width of the brunhes anomaly on evenly spaced marine magnetic profiles over the east scotia ridge provide new estimates of scotia sandwich plate spreading rates since there are no stable fracture zones in the east scotia sea the mean azimuth of sea floor fabric mapped by sidescan is used to constrain the direction of spreading 18 newrate estimates and four azimuths from the east scotia ridge are combined with 68 selected earthquake slip vectors from the boundaries of the scotia sea in a least squares inversion for the best fitting set of euler poles and angular rotation rates describing the present day motions of the scotia and sandwich plates relative to south america and antarctica our preferred model tlp2003 gives poles that are similar to previous estimates except for scotia plate motion with respect to south america which is significantly different from earlier estimates predicted rates of motion also differ slightly our results are much more robust than earlier work we examine the implications of the model for motion and deformation along the various plate boundaries with particular reference to the north and south scotia ridges where rates are obtained by closure

evolution of cloud to ground lightning and storm structure in the spencer south dakota tornadic supercell of 30 may 1998 abstract on 30 may 1998 a tornado devastated the town of spencer south dakota the spencer tornado rated f4 on the fujita tornado intensity scale was the third and most intense of five tornadoes produced by a single supercell storm during an approximate 1 h period the supercell produced over 76 positive cloud to ground cg lightning and a peak positive cg flash rate of 18 flashes min 1 5 min average during a 2 h period surrounding the tornado damage earlier studies have reported anomalous positive cg lightning activity in some supercell storms producing violent tornadoes however what makes the cg lightning activity in this tornadic storm unique is the magnitude and timing of the positive ground flashes relative to the f4 tornado in previous studies supercells dominated by positive cg lightning produced their most violent tornado after they attained their maximum positive ground flash rate whenever the rate exceeded 1 5 flashes min 1 further tornadogenesis often occurred during a lull in c

the june 22 tropical squall line observed during copt 81 experiment electrical signature associated with dynamical structure and precipitation the tropical convection experiment copt 81 convection profonde tropicale was carried out near korhogo northern ivory coast during may and june 1981 the june 22 squall line was observed using meteorological and electrical equipment the frontal part was characterized by a heavy precipitation core associated with strong convection it was followed by a region of weak precipitation and a wide area of stratiform rain the characteristic of this squall line resides in the two dimensional structure of the observed three dimensional wind fields with intense convection ahead of the heavy precipitation core electrical measurements indicate that electrostatic field changes at ground level occurred in the weak precipitation zone and in the stratiform precipitation region no particular electrical activity was observed in the most convective but shallow part of the squall line a classical dipole structure appeared within the stratiform area the stationary electrical structure was coherent with the stationary dynamics and precipitation pattern of the squall line

tropical island convection in the absence of significant topography part i life cycle of diurnally forced convection abstract diurnally forced convection was observed over the tiwi islands north of the australian continent as part of the maritime continent thunderstorm experiment immature peninsula scale 5 15 km sea breezes were observed to initiate moist convection early each day principally through convergence that results from the confluence or collision of peninsula breeze fronts convection initiated by peninsula scale breezes usually fails to organize beyond a small cluster of cells and dissipates as a local event mature island scale 100 km breezes develop by late morning and subsequently play a pivotal role in the forcing and evolution of organized convection the initiation of mesoscale convective systems mcss is observed to be a direct consequence of breeze front collisions for only 20 of the days on which organized convection develops this is referred to as type a forcing and it occurs when normal convective development is delayed or otherwise suppressed type a forcing is nature s backup mech

microphysical characteristics of mjo convection over the indian ocean during dynamo the microphysical characteristics of precipitating convection occurring in various stages of the madden julian oscillation mjo over the indian ocean are determined from data obtained from the national center for atmospheric research dual polarimetric doppler s band radar s polka deployed as part of the dynamics of the mjo dynamo field experiment active mjo events with increased rainfall occurred in october november and december 2011 during each of these active mjo phases in addition to enhanced rainfall convection became deeper and ice phase microphysics played a greater role s polka consistently showed nonoriented small ice particles dominating the radar echoes at altitudes of 9 10 km dry aggregates concentrated between 7 and 9 km and wet aggregates and graupel near the melting level 5 km graupel occurred mainly in actively convective towers while the wet aggregates occurred almost exclusively in the stratiform regions of mesoscale convective systems mcss during each of the three multiweek mjo active phases the maximum rainfall occurred in short bursts lasting a few days each multiday rainy period began with deepening convective elements and a concurrent increase in occurrence of dry aggregates which maximized just prior to organization into mcss the peak rainfall occurrence coincided with the maximum coverage of the radar domain by mcss reflecting large stratiform regions that exhibited the most frequent occurrence of wet aggregates during the december active mjo phase however the mcss were shallower and had a slightly lower tendency for wet aggregates in the stratiform regions and therefore generally weaker brightbands

methane hydrate and free gas on the blake ridge from vertical seismic profiling seismic velocities measured in three drill holes through a gas hydrate deposit on the blake ridge offshore south carolina indicate that substantial free gas exists to at least 250 meters beneath the bottom simulating reflection bsr both methane hydrate and free gas exist even where a clear bsr is absent the low reflectance or blanking above the bsr is caused by lithologic homogeneity of the sediments rather than by hydrate cementation the average methane hydrate saturation above the bsr is relatively low 5 to 7 percent of porosity which suggests that earlier global estimates of methane in hydrates may be too high by as much as a factor of 3

a case study of convective organization into precipitating lines in the southwest amazon during the wetamc and trmm lba 1 a case study of convective development in the southwest amazon region during the wet season atmospheric mesoscale campaign wetamc and tropical rainfall measuring mission trmm large scale biosphere atmosphere lba experiment in amazonia is presented the convective development during 7 february 1999 is shown to occur during a period of very weak large scale forcing in the presence of topography and deforestation the available data include dual doppler radar analysis radiosonde launches and surface and boundary layer observations the observational analysis is complemented with a series of model simulations using the rams with 2 km resolution over a 300 km 300 km area forced by a morning radiosonde profile a comparison of the observed and simulated thermodynamic transformation of the boundary layer and of the formation of convective lines and of their kinematic and microphysical properties is presented it is shown that only a few very deep and intense convective cells are necessary to explain the overall precipitating line formation and that discrete propagation and coupling with upper atmosphere circulations may explain the appearance of several lines the numerical simulation indicates that topography may be the cause of initial convective development although later on the convective line is parallel to the midlevel shear there are indications that small scale deforestation may have an effect on increasing rainfall in the wet season when the large scale forcing is very weak

hydrometeor mass number and space charge distribution in a hector squall line 1 videosonde data from an australian squall line were combined with a radar echo profile to construct a conceptual model of hydrometeor mass number and space charge evolution two step hydrometeor growth modes were suggested low level warm rain frozen drop and high level graupel ice crystals a riming electrification mechanism successfully explained the charge distribution a warm rain frozen drop process was active in the forward area of the convective region and frozen drop growth was highly active near the 0 c level ice crystals which electrified frozen drops positively increased in number as they were lifted graupel growth was enhanced and additional charge separation occurred between ice crystals and graupel in the upper level large negative graupel fell at the rear of the convective region while positive ice crystals and small negative graupel were transported into the anvil the reason for high lightning frequencies in a squall line over a maritime continent is also discussed

on the interannual variability of ocean temperatures around south georgia southern ocean forcing by el nino southern oscillation and the southern annular mode abstract the ocean around south georgia in the southwest atlantic sector of the southern ocean is highly productive with large stocks of antarctic krill supporting extensive colonies of marine and land based predators the operation of this ecosystem is strongly influenced by physical forcings and the role of the el nino southern oscillation enso phenomenon has been highlighted previously here we examine in detail the transmission of enso signals to south georgia and investigate other sources of interannual variability enso variability generates anomalies in sea surface temperature sst across the south pacific via atmospheric teleconnections these anomalies are advected toward south georgia within the antarctic circumpolar current acc and previous studies have focussed on long period advection order of 2 3 years from the southwest pacific we observe here however that the region close to the antarctic peninsula in the southeast pacific is especially susceptible to enso forcing via anomalous meridional winds this induces sst anomalies that are advected to south georgia on a much more rapid timescale order 5 6 months the phasing of these teleconnections is such that anomalies that reach the southeast pacific from farther west tend to be reinforced here by air sea ice interaction we also find an important role for the southern annular mode sam in determining sst variability at south georgia this is a circumpolar mode of climate variability and thus can readily influence local sst at south georgia directly the sam is however not perfectly zonally symmetric and like enso has a particular impact on meridional winds in the southeast pacific the average timescale for sam influence on south georgia sst is shorter than that of enso since it includes a stronger component of direct local forcing the south georgia ecosystem is not self sustaining with import of krill from breeding and nursery grounds upstream in the acc being important we speculate here that these varying meridional winds close to the antarctic peninsula play a direct role in promoting restricting the injection of shelf waters and the krill therein into the acc following which anomalies in krill density would be advected toward south georgia this offers a dynamical mechanism that might contribute to interannual changes in biological communities at south georgia in addition to existing theories both sam and enso have shown long period changes in recent decades with enso exhibiting a higher preponderance of el nino events compared with la nina events and the sam showing a marked trend toward a higher index state such long period behaviour is likely to induce changes in the south georgia ecosystem via their impacts on advection and sst for which an understanding of the physical mechanisms elucidated here will be key to unravelling

convection and easterly wave structures observed in the eastern pacific warm pool during epic 2001 abstract during september october 2001 the east pacific investigation of climate processes in the coupled ocean atmosphere system epic 2001 intertropical convergence zone itcz field campaign focused on studies of deep convection in the warm pool region of the eastern pacific this study combines c band doppler radar sounding and surface heat flux data collected aboard the r v ronald h brown during epic to describe the kinematic and thermodynamic states of the itcz environment together with tendencies in convective structure lightning rainfall and surface heat fluxes as a function of 3 5 day easterly wave phase three easterly waves were observed at the location of the r v brown during epic 2001 wind and thermodynamic data reveal that the wave trough axes exhibited positively correlated u and winds a slight westward phase tilt with height and relatively strong weak northeasterly tropospheric shear following the trough ridge axis temperature and humidity perturbations exhibited mid to

a squall line in southern germany kinematics and precipitation formation as deduced by advanced polarimetric and doppler radar measurements abstract a multiscale analysis of a squall line system is reported in this paper it is shown that the squall line was initiated as part of a synoptic scale frontal zone the main emphasis then is on the polarimetric and doppler radar measurements which give insight into the meso and microscale structure of the kinematics and the precipitation microphysics especially within the new cells growing ahead of the squall line and within the main precipitation system the principal polarimetric measurements considered are the differential reflectivity zdr and a related new derived parameter termed the difference reflectivity or zdp which is useful in detection of rain ice mixed phase precipitation a limited amount of time series data have been analyzed to derive the specific differential phase kdp and the backscatter differential phase between horizontal and vertical polarizations a brief overview of the microphysical interpretation of these parameters is provided the newly grown clouds are identifi

seafloor reflectivity an important seismic property for interpreting fluid gas expulsion geology and the presence of gas hydrate a bottom simulating reflection bsr is a seismic reflectivity phenomenon that is widely accepted as indicating the base of the gas hydrate stability zone the acoustic impedance difference between sediments invaded with gas hydrate above the bsr and sediments without gas hydrate but commonly with free gas below are accepted as the conditions that create this reflection the relationship between bsrs and marine gas hydrate has become so well known since the 1970s that investigators when asked to define the most important seismic attribute of marine gas hydrate systems usually reply a bsr event research conducted over the last decade has focused on calibrating seafloor seismic reflectivity across the geology of the northern gulf of mexico gom continental slope surface to the seafloor this research indicates that the presence and character of seafloor bright spots sbs can be indicators of gas hydrates in surface and near surface sediments figure 1 it has become apparent that sbss on the cont

ice crystal habits and growth processes in stratiform clouds with embedded convection examined through aircraft observation in northern china abstractice crystal habits and growth processes in two cases of stratiform clouds with embedded convection are investigated using data observed simultaneously from three aircraft on 18 april 2009 and 1 may 2009 as part of the beijing cloud experiment bce the results show that the majority of ice crystal habits found in the two cases at temperatures between 0 and 16 c included platelike needle column capped column dendrite and irregular a mixture of several ice crystal habits was identified in all of the clouds studied however the ice crystals recorded in the embedded convection regions contained more dendrites and possessed heavier riming degrees and the ice crystals identified in the stratiform clouds contained more hexagonal plate crystals both riming and aggregation processes played central roles in the broadening of particle size distributions psds and these processes were more active in embedded convection regions than in stratiform regions however riming was more prevalent in the

fracture networks and hydrate distribution at hydrate ridge oregon abstract analysis of resistivity at the bit rab images acquired during ocean drilling program odp leg 204 to southern hydrate ridge oregon reveals changes in the distribution and orientation of resistive fractures between the different hydrologic provinces sampled fractures on the ridge crest at sites 1247 1248 and 1250 are typically high angle 60 with isotropically distributed strikes while those on the ridge flanks at sites 1244 1246 have lower dips 20 60 and strike parallel to the trend of the ridge the eastern slope basin site 1251 lacks significant fracturing these differences indicate that the minimum principal stress 3 direction rotates to horizontal at the ridge crest as a result of topographically driven extension and gravitational collapse of the ridge chaotic fracturing on the ridge crest results from the interaction of the stress state and free gas migration which is confined to high permeability sediments and fracture zones by capillary pressure constraints in contrast on the ridge flanks well ordered fractures that agree with stress orientations determined from borehole breakouts result from an obliquely dipping 3 and the predominance of aqueous rather than gaseous flow

advances in the estimation of ice particle fall speeds using laboratory and field measurements accurate estimates for the fall speed of natural hydrometeors are vital if their evolution in clouds is to be understood quantitatively in this study laboratory measurements of the terminal velocity yt for a variety of ice particle models settling in viscous fluids along with wind tunnel and field measurements of ice particles settling in air have been analyzed and compared to common methods of computing yt fromthe literature it is observed that while these methods work well for a number of particle types they fail for particles with open geometries specifically those particles for which the area ratio ar is small ar is defined as the area of the particleprojectednormaltotheflow dividedbytheareaofacircumscribing disc inparticular thefallspeeds of stellar and dendritic crystals needles open bullet rosettes and low density aggregates are all overestimated these particle types are important in many cloud types aggregates in particular often dominate snow precipitation at the ground and vertically pointing doppler radar measurements based on the laboratory data a simple modification to previous computational methods is proposed based on the area ratio this new method collapses the available drag data onto an approximately universal curve and the resulting errors in the computed fall speeds relative to the tank data are less than 25 in all cases comparison with the much more scattered measurements of ice particles falling in air show strong support for this new method with the area ratio bias apparently eliminated

an overview of the microphysical structure of cirrus clouds observed during emerald 1 high resolution ice microphysical turbulence heat and water vapour flux data in cirrus clouds were collected by the airborne research australia s ara egret grob 520t research aircraft during the first egret microphysics with extended radiation and lidar experiment emerald 1 the in situ cirrus measurements were guided by simultaneous airborne lidar measurements collected by the ara super king air research aircraft which flew below the cirrus and whose horizontal position was synchronized with the egret this allowed the microphysics and turbulence measurements to be interpreted and evaluated within the context of large scale cirrus structure and its evolution a significant feature of the clouds observed was the presence on occasion of active convective columns large variations in the cirrus dynamics were observed with significant variations in the ice crystal habit from cloud top to cloud base and within the evaporating fall streaks of precipitation however on average the picture presented is consistent with that shown by heymsfield and miloshevich and by kajikawa and heymsfield with the upper supersaturated region of the cloud acting as an active particle generation zone where homogeneous nucleation proceeds apace ice crystals there are initially dominated by small irregular or spheroidally shaped particles some of which can be identified as proto or germ rosettes these are then observed to grow into more open bullet rosette and columnar types as they fall into the less supersaturated middle and lower layers of the cloud the mean recognisable ice particle size fell within a very narrow size band 70 90 m but the actual size distribution is thought to increase in a continuous manner to smaller sizes however there are currently instrument limitations that make it difficult to confirm this unambiguously unlike most previous studies however the cirrus clouds observed here were mostly devoid of pristine plate like crystals as nucleation and growth within the planar growth regime was rarely encountered during some cases bullet rosettes once formed did undergo transition to the plate growth regime with complex crystal shapes resulting the mean size of pristine bullet rosettes was again confined to a relatively narrow range the likely nucleation processes dominating in cirrus clouds are discussed in the light of the observations very high concentrations of small ice crystals were sometimes detected concentrations reaching a maximum of 10000 l 1 there is strong evidence supporting these high concentrations which are probably produced by the homogeneous freezing of aerosol

evidence for fluid circulation overpressure and tectonic style along the southern chilean margin the southern chilean convergent margin between 50 and 57 s is shaped by the interaction of the three main plates antarctic south america and scotia north of 53 s the convergence between antarctic and south america plates is close to orthogonal to the continental margin strike here the deformational style of the accretionary prism is mainly characterized by seaward verging thrusts and locally by normal faults and fractures a very limited lateral extension of prism a very shallow dip 6 decollement and subduction of a thick and relatively undeformed trench sedimentary sequence south of 53 s convergence is oblique to the margin locally the trench sediments are proto deformed by double vergence thrusting and the front of the prism grows through landward verging thrusting the decollement is sub horizontal and deep involving most of the sediment over the oceanic crust in the accretionary process building a comparatively wide and thicker prism a bottom simulating reflector is present across the whole prism to the abyssal plan suggesting the presence of gas in the sediments the analysis of p and s wave velocity reflectivity sections derived by amplitude versus offset technique avo detailed velocity information and the velocity derived sediment porosity have been integrated with the structural analysis of the accretionary prism of two selected pre stack depth migrated seismic lines aiming to explain the relation between fluid circulation and tectonics accretion along double vergence thrust faults may be associated with the presence of overpressured fluid which decreases the effective shear stress coefficient along the main decollement and within the sediments and modify the rheolgical properties of rocks the presence of an adequate drainage network represented by interconnected faults and fractures affecting the entire sedimentary sequence can favour the escape of pore fluid toward the sea bottom while less permeable and not faulted sediments can favour fluid accumulations gravitational and tectonic dewatering and stratigraphy could control the consolidation and the pore overpressure of sediments involved in subduction along the trench the results of our analysis suggest the existence of a feedback between tectonic style and fluid circulation

a radar and electrical study of tropical hot towers abstract radar and electrical measurements for deep tropical convection are examined for both break period and monsoonal regimes in the vicinity of darwin australia break period convection consists primarily of deep continental convection whereas oceanic based convection dominates during monsoonal periods associated with the monsoon trough over darwin order of magnitude enhancements in lightning flash rates for the break period regime are associated with 10 20 db enhancements in radar reflectivity in the mixed phase region of the convection compared with the monsoonal regime the latter differences are attributed to the effect of convective available potential energy cape and its nonlinear influence on the growth and accumulation of ice particles aloft which are believed to promote charge separation by differential particle motions cape in turn is largely determined by the boundary layer wet bulb temperature modest differences 1 3 c in wet bulb potential temperature between land and s

geochemical constraints for the formation and dissociation of gas hydrate in an area of high methane flux eastern margin of the japan sea abstract the umitaka spur in the joetsu basin on the eastern margin of the japan sea is characterized by a number of features indicative of high methane flux such as a bsr and gas plumes rising through the water column these are likely linked to the presence of hydrocarbon source rocks underneath the spur the interstitial water chemistry at the spur was measured in order to delineate the behavior and evolution of the gas hydrate system across the region the sulfate depth profiles indicate that the smi depths become shallower toward the crest of the spur and are shallowest less than 200 cmbsf at two plume sites suggesting that the methane fluxes are highest around the plumes depth profiles of dissolved cl all fall into one of four distinguishable trends type i where concentrations linearly increase with sediment depth type ii where concentrations linearly decrease with depth type iii where concentrations remain constant and type iv where concentrations exhibit negative spikes caused by dissociation of gas hydrate during core recovery and handling type i cores commonly recovered at central plume site are characterized not only by steep cl gradients 13 2 to 51 0 mm m but also extreme depletions in d and 18o 0 97 to 0 54 vsmow m for dh2o and 0 16 to 0 10 vsmow m for 18oh2o suggesting gas hydrate formation at shallow depth the cl gradients of type ii cores recovered from the southern part of the spur have little variation 14 8 to 8 3 mm m gas hydrate dissociation along base of the gas hydrate stability zone best explains both the similar pattern of freshening with depth and the widespread distributions of type ii cores although gas hydrate dissociation is known to release isotopically heavy water type ii cores show progressive depletions of both d and 18o with downward depth the apparent contradiction between cl concentrations and the isotopic compositions of type ii cores is likely due to re equilibration by strong burial diagenesis observed all over the japan sea sediments regional dissociation of gas hydrate is likely to have been triggered by sea level drop which facilitated dissociation of subsurface gas hydrate

evolution of microphysical structure of a subtropical squall line observed by a polarimetric radar and a disdrometer during opacc in eastern china the evolution of the microphysical structures of a subtropical squall line observed during the observation prediction and analysis of severe convection of china opacc field campaign in eastern china is documented in this paper the data collected from a c band polarimetric doppler radar reflectivity z differential reflectivity zdr and specific differential phase kdp and a disdrometer are used to investigate the variations of microphysical characteristics within the convective region during the formative intensifying and mature stages of the squall line the microphysical characteristics of the squall line are noticeably different among these three stages when the squall line develops from the formative stage to the mature stage its radar derived drop size distribution dsd in the convective region evolves from continental like convection to more maritime like convection contrary to previous studies the dsd characteristics of a convective line may not be simply locked to a geographical location but varied extensively throughout its life cycle the polarimetric radar derived liquid water content below the freezing level in the convective region is three times higher than the ice water content above the freezing level this in conjunction with a low cloud base 0 68 km and a high freezing level 5 km indicates a deep warm cloud layer and the dominance of the warm rain process within this squall line

aircraft observations of the influence of electric fields on the aggregation of ice crystals aircraft observations of ice crystal size and habit distributions in the cirrus outflow from deep convection at several geographic locations are reported in situ measurements were made in the outflow from maritime thunderstorms near kwajalein part of the marshall islands and of thunderstorms with more continental aerosol concentrations both in the united states and near darwin australia over the tiwi islands images of chain like aggregates of small ice crystals some with plate like shapes were observed with a state of the art microphysics probe in the outflow regions of continental storms that were typically highly electrified displaying lightning the chains were not found in the outflow regions of maritime storms that are typically less electrically active the striking similarity between these images and previous laboratory measurements of ice aggregation in electric fields are remarked upon this evidence is used to support the theory that chain aggregates of ice crystals may be common in fully glaciated regions of continental thunderstorms where ice particle number densities are high and their presence is due to the electric field alignment of ice crystals with subsequent enhancement of the aggregation process by dipole induction resulting in short range attractive inter particle forces it is not confirmed where in the storm the aggregates were typically formed however in the darwin thunderstorms they were noted to occur with the highest frequency towards the cirrus outflow base when the cirrus base altitude was high and generally decreased in frequency with increasing distance from the storm the potential consequences of electrically enhanced aggregation in continental storms and related electric field mechanisms along with the role of homogeneous freezing in intense thunderclouds are discussed copyright 2005 royal meteorological society

estimating the amount of gas hydrate and free gas from marine seismic data marine seismic data and well log measurements at the blake ridge offshore south carolina show that prominent seismic bottom simulating reflectors bsrs are caused by sediment layers with gas hydrate overlying sediments with free gas we apply a theoretical rock physics model to 2 d blake ridge marine seismic data to determine gas hydrate and free gas saturation high porosity marine sediment is modeled as a granular system where the elastic wave velocities are linked to porosity effective pressure mineralogy elastic properties of the pore filling material and water gas and gas hydrate saturation of the pore space to apply this model to seismic data we first obtain interval velocity using stacking velocity analysis next all input parameters to the rock physics model except porosity and water gas and gas hydrate saturation are estimated from geologic information to estimate porosity and saturation from interval velocity we first assume that the entire sediment does not contain gas hydrate o

high resolution modelling of the shelf and open ocean adjacent to south georgia southern ocean abstract the marine ecosystem on the shelf and open ocean adjacent to south georgia is extraordinarily rich with a history of commercial exploitation although much progress has been made attempts at modelling and hence better understanding this system have consistently been hampered by the poor representation of key physical processes in global or regional ocean general circulation models here we present the development of a high resolution 3d hydrodynamic model of the south georgia shelf and the adjacent open ocean including a novel method for prescribing freshwater fluxes the ability of the model to reproduce the observed oceanography of the region is quantified by comparisons with data from tide gauges at south georgia with satellite derived sea surface temperatures and with an extensive ctd dataset collected during january april 1995 predicted cotidal charts for the diurnal tides o1 and k1 show a periodic amplification in both the current and elevation fields at the shelf edge suggesting the presence of a diurnally forced continental shelf wave this could have important implications for processes such as larval transport and retention the comparison with ctd data reveals mean and root mean square errors in temperature salinity of 0 27 c 0 07 and 0 64 c 0 23 respectively vertical profiles of potential temperature and salinity on the shelf agree acceptably well with observations but there is a tendency for the model to under predict the density contrast between surface and bottom waters the main limitation on model accuracy is found to be the large scale forcing releasing a passive tracer into the model transport and retention pathways are identified including a prevalence for tracer export from the shelf to the west of south georgia and a transport pathway linking south georgia and shag rocks significantly the model suggests this to be a unidirectional link from south georgia to shag rocks with possible significance for fisheries management the implications of these results in the context of the south georgia ecosystem are discussed briefly demonstrating the usefulness of this new tool for interdisciplinary studies of the region

hydrographic control of the marine ecosystem in the south shetland elephant island and bransfield strait region the south shetland elephant island and bransfield strait region of the west antarctic peninsula is an important spawning and nursery ground of antarctic krill euphausia superba and is an important source of krill to the southern ocean krill reproductive and recruitment success hence supply of krill to predator populations locally and in downstream areas are extremely variable on interannual and longer time scales interannual ecosystem variability in this region has long been recognized and thought related to el nino southern oscillation enso events but understanding of how has been limited by the hydrographic complexity of the region and lack of appropriate ocean atmosphere interaction models this study utilizes multidisciplinary data sets collected in the region from 1990 to 2004 by the u s antarctic living marine resources amlr program we focus on hydrographic conditions associated with changes in the distribution abundance and composition of salp and copepod dominated zooplankton assemblages during 1998 and 1999 years characterized respectively by a strong el nino event and la nina conditions we provide detailed analyses of hydrographic biological and ecological conditions during these dichotomous years in order to identify previously elusive oceanographic processes underlying ecosystem variability we found that fluctuations between salp dominated coastal zooplankton assemblages and copepod dominated oceanic zooplankton assemblages result from the relative influence of weddell sea and oceanic waters and that these fluctuations are associated with latitudinal movement of the southern antarctic circumpolar current front saccf latitudinal movements of the saccf can be explained by meridional atmosphere teleconnections instigated in the western tropical pacific ocean by enso variability and are consistent with out of phase forcing in the south pacific and south atlantic oceans by the antarctic dipole high latitude climate mode during el nino decreased northwest winds equatorward movement of the saccf and an intensified weddell gyre allow weddell sea water to flow into eastern bransfield strait during these periods mixing between oceanic and coastal waters is reduced chlorophyll a concentrations are low salps numerically dominate the zooplankton and krill recruitment success is poor during la nina increased and more frequent northwest winds and poleward movement of the saccf allows increased influence of oceanic waters and mixing of these with cold coastal waters these periods are characterized by numerical dominance of copepods elevated concentrations of oceanic zooplankton taxa and phytoplankton blooms that promote krill reproduction and recruitment success hydrographic and ecological changes after the 1998 el nino are associated with a shift from frequent el ninos to the prevalence of la nina and neutral conditions and conform to a decadal scale climate regime shift in the antarctic peninsula region