distribution of helicity cape and shear in tropical cyclones abstract the previous study of helicity cape and shear in hurricane bonnie 1998 was extended to all eight tropical cyclones sampled by nasa during the convection and moisture experiments camex storms were categorized as having large or small ambient vertical wind shear with 10 m s 1 as the dividing line in strongly sheared storms the downshear mean helicity exceeded the upshear mean by a factor of 4 as in the previous study the helicity differences resulted directly from the tropical cyclone response to ambient shear with enhanced in up out flow and veering of the wind with height present downshear cape in strongly sheared storms was 60 larger downshear mean inflow near the surface and the depth of the inflow layer each were 4 times larger downshear at more than 30 of observation points outside the 100 km radius in the downshear right quadrant midlatitude empirical parameters indicated a strong likelihood of supercells no such points existed upshear in highly sheared storms much small

intense sub kilometer scale boundary layer rolls observed in hurricane fran high resolution observations obtained with the doppler on wheels dow mobile weather radar near the point of landfall of hurricane fran 1996 revealed the existence of intense sub kilometer scale boundary layer rolls that strongly modulated the near surface wind speed it is proposed that these structures are one cause of geographically varying surface damage patterns that have been observed after some landfalling hurricanes and that they cause much of the observed gustiness bringing high velocity air from aloft to the lowest observable levels high resolution dow radar observations are contrasted with lower resolution observations obtained with an operational weather radar which underestimated peak low level wind speeds

stability metastability and elastic properties of a dense silica polymorph seifertite 1 dense silica polymorphs with sixfold coordinated si have been found in snc and lunar meteorites and may be important minerals for silica rich components in the lower mantle however the stable crystal structure in the lower mantle and properties of dense silica remain controversial under stable heating and quasi hydrostatic stress conditions we found that the cacl2 type undergoes a phase transition to the pbo2type seifertite at 130 140 gpa and 2500 k our data suggest that this phase transition occurs at a greater depth than the perovskite postperovskite transition in the lowermost mantle the molar volume measured at 1 bar is the smallest among the reported silica polymorphs therefore having the highest calculated density and in excellent agreement with recent first principles calculations the greater molar volume of seifertite found in the shergottite meteorite and previous experiments supports a metastable synthesis of the phase outside its stability field our data combined with the hugoniots of silica polymorphs also rule out the possibility of the formation of seifertite in the meteorite within its stability field we found very little change in bulk sound speed across the cacl2 type seifertite transition if shear wave velocity decreases at the transition to seifertite as suggested by some computational studies this silica transition may provide an alternative explanation for the discontinuities with a shear wave velocity decrease found at depths greater than the d discontinuity

cape in tropical cyclones abstractconvective available potential energy cape and the vertical distribution of buoyancy were calculated for more than 2000 dropsonde soundings collected by the noaa gulfstream iv aircraft calculations were done with and without the effects of condensate loading entrainment and the latent heat of fusion cape showed larger values downshear than upshear within 400 km of the center consistent with the observed variation of convective intensity the larger downshear cape arose from i higher surface specific humidity ii lower midtropospheric temperature and for entraining cape iii larger free tropospheric relative humidity reversible cape had only one half the magnitude of pseudoadiabatic cape as shown previously reversible cape with fusion closely resembled pseudoadiabatic cape without fusion entrainment had the most dramatic impact entraining cape was consistent with the observed radial distribution of convective intensity displaying the largest values downshear at inner radii with

buoyancy and shear characteristics of hurricane tornado environments abstract detailed composite profiles of temperature moisture and wind are constructed for tornado environments in tropical cyclones that affected the united states during the period 1948 86 winds are composited in components radial and tangential to the tropical cyclone center at observation time guided by observed patterns of tornado occurrence composites are constructed for a variety of different stratifications of the data including proximity to tornadoes position relative to the cyclone center time of day time after cyclone landfall cyclone translation speed and location of landfall the composites are also compared to composite soundings from great plains tornado environments a variety of sounding parameters am examined to see which are most closely related to the patterns of tornado distribution lower tropospheric vertical shears are generally stronger in the tropical cyclone tornado environments than on the great plains vertical shear and helicity parameters along with 700 hpa wind s

sedimentology taphonomy and palaeoecology of a laminated plattenkalk from the kimmeridgian of the northern franconian alb southern germany abstract at wattendorf in the northern franconian alb southern germany centimetre to decimetre thick packages of finely laminated limestones plattenkalk occur intercalated between well bedded graded grainstones and rudstones that blanket a relief produced by now dolomitized microbialite sponge reefs these beds reach their greatest thickness in depressions between topographic highs and thin towards and finally disappear on the crests the early late kimmeridgian graded packstone bindstone alternations represent the earliest plattenkalk occurrence in southern germany the undisturbed lamination of the sediment strongly points to oxygen free conditions on the seafloor and within the sediment inimical to higher forms of life the plattenkalk contains a diverse biota of benthic and nektonic organisms excavation of a 13 cm thick plattenkalk unit across an area of 80 m2 produced 3500 fossils which with the exception of the bivalve aulacomyella exhibit a random stratigraphic distribution two thirds of the individuals had a benthic mode of life attached to hard substrate this seems to contradict the evidence of oxygen free conditions on the sea floor such as undisturbed lamination presence of articulated skeletons and preservation of soft parts however palaeoecological and taphonomic analyses indicate that the benthic faunal elements are allochthonous having settled out of suspension and thus must have been derived from hard substrate areas of neighbouring topographic highs solely the bivalve aulacomyella which occurs concentrated on a single bedding plane may have colonised the plattenkalk depression during brief periods of oxygenation alternatively a pseudoplanktonic mode of life attached to floating sea weed is envisaged for the bivalve the formation of the plattenkalk is related to local and global factors a drop in relative sea level caused the death of the microbialite sponge reefs restricted circulation in depressions between the crests of the former reefs led to anoxic conditions and the formation of finely laminated sediments stabilised by microbial mats the small depressions received sediment and skeletal elements of benthic organisms that were swept off neighbouring topographic highs by storms and that entered the depressions partly as turbidity currents partly as suspension clouds a rise in the relative sea level finally terminated the restricted circulation in the depressions and closed the taphonomic window that led to the preservation of the plattenkalk biota

multiple phase analysis of the shear velocity structure in the d region beneath alaska a large data set more than 990 total waveforms comprised of north american station recordings of a variety of long period s phases s scs sdiff ss sscs sks skks from 36 earthquakes in western pacific subduction zones is analyzed to determine characteristics of the shear velocity structure in the d region beneath alaska three hypotheses that have been proposed to explain observed scs precursors and s waveform distortions for this region are appraised with the multiple phase data set and the radial and lateral variations of the shear velocity structure in the 1500 km broad portion of d sampled are also assessed the observed travel time and waveform variations may result from diffraction by near source slab structure scattering by low velocity heterogeneity in the lower mantle or interaction with complex velocity gradients in d associated with a deep mantle velocity discontinuity we utilize waveform modeling and differential time analysis to resolve greater detail of the structure than can presently be obtained by standard travel time tomography techniques and find that the discontinuity model is most consistent with the data subdivision of the data by source region and source to receiver azimuth establishes that the observations exhibit fairly stable behavior which is consistent with extensive local stratification of d the data show sufficient coherence over the 1500 km broad region that we find it useful to present a local average radial model the preferred model sylo has a 2 75 velocity increase 243 km above the core mantle boundary and a negative velocity gradient within the d layer analysis of sks s sks scs and sks skks differential times also indicates that the outermost 100 km of the core below the fast d region underlying alaska must be slower than the prem structure the observations exhibit significant scatter most of which can be attributed to unmodeled heterogeneity in the midmantle and near source regions as well as lateral variations in the d region the complex structure of d that we prefer may be associated with large scale downwelling in the lower mantle but it is not certain whether it is a purely thermal or a combined chemical and thermal effect

evidence of a laterally variable lower mantle structure from p and s waves summary examples of grafenberg array data showing anomalous p waves which typically arrive 3 5s after the direct p wave and which have a slowness 0 7 0 8 sdeg smaller than direct p are presented this additional phase is most frequently observed for events located in the ne portion of the southern kurile island subduction zone 73 80 from grafenberg but systematically disappears for events in the sw portion of this zone because of the magnitude of the slowness difference these observations cannot be attributed to a complex source rupture process nor to multipathing through the descending slab likewise they may not be accounted for by near receiver structure because these phases are not seen for all kurile events if present they appear at all stations of the array but they follow direct p too closely to be a multiple from the moho therefore we conclude they are very likely caused by lower mantle velocity structure the most likely explanation is the presence of a p velocity jump of about 3 per cent approximately 290 km above the core mantle boundary since such a reflector in the lowermost mantle not only gives a good fit of traveltimes and slowness but is also able to model the waveform and the amplitudes of this additional p phase the distribution of bounce points on this reflector for the kurile events indicates a lateral extension of this velocity anomaly under northern siberia of about 150 km by at least 200 km the best fitting s wave model has a reflector in the same depth but the velocity contrast seems to be only about 2 per cent suggesting a different behaviour of the p and s velocity in d few events from other regions in this distance range are suitable for a definitive analysis of this kind from among this group some observations indicate a lower mantle anomaly under the lomonosow ridge and under northern greenland but since the lower mantle under western siberia northern novaya zemlya the azores islands region and the ussr afghanistan border region does not produce an additional phase in the grafenberg recordings it is very unlikely that such a velocity anomaly in the lowermost mantle is a global feature

the origin of d reflections a systematic study of seismic array data sets regional seismic studies of the earth s deep mantle indicate the presence of p and s wave reflectors at the top of the d layer such reflectors appear to be laterally intermittent occur at a range of depths and produce waveforms whose amplitude and polarity differ at different locations a number of possible explanations for d reflections have been proposed including a phase change from perovskite to post perovskite thermal or thermochemical discontinuities generated by subducted slabs alignment of anisotropic minerals and global or small scale chemical heterogeneity arising perhaps from core mantle interactions or primitive material however some of the observed heterogeneity in d structure may be related to lack of consistency between the style quality and number of seismic observations in different regions as well as complexity in wave propagation due to 3 d structure in this study we present a compilation of observations of d reflections for regions in which 1 a reflector is seen in both p and s wave arrivals and 2 consistent array seismology techniques have been applied to infer the properties of the reflectors using a recent monte carlo thermodynamic modelling method to convert changes in chemistry and mineralogy into changes in seismic velocity we compare the fit of different isotropic thermochemical structures to the observed seismic properties of d reflections namely the polarity and amplitude of the waveforms our results indicate that it may be possible to discriminate between different possible origins for d reflections on the basis of polarity observations alone amplitude measurements may provide further constraints but must be treated with caution due to a large number of factors which can influence waveform amplitudes in regions such as the caribbean which are characterized by high amplitude negative polarity p waveforms and positive polarity s waveforms a phase change from perovskite to post perovskite provides the most likely explanation for the discontinuity however in other regions notably siberia and the central pacific p and s waveforms both display a positive polarity and multiple explanations for the discontinuity are possible including subduction related chemical heterogeneity and anisotropy

an air sea interaction theory for tropical cyclones part ii evolutionary study using a nonhydrostatic axisymmetric numerical model abstract in part i of this study an analytical model for a steady state tropical cyclone is constructed on the assumption that boundary layer air parcels are conditionally neutral to displacements along the angular momentum surfaces of the hurricane vortex the reversible thermodynamics implied by this assumption allows the mature storm to be thought of as a simple carnot engine acquiring heat at the high temperature ocean surface and losing heat near the low temperature tropopause although the oceanic heat source is universally recognized as the sine qua non for the mature hurricane there is also wide acceptance of conditional instability of the second kind cisk which makes no specific reference to surface heat fluxes as the formative mechanism this ambivalence is seen in that all numerical simulation studies find it essential to have transfer from the ocean surface yet all start from a conditionally unstable atmosphere the hypothesis put forward in part i based on the steady state theory is t

modelling d structure beneath central america with broadband seismic data deep south american events recorded at distances between 70 and 96 are used to constrain the lower mantle structure beneath central america employing data from the terrascope bdsn iris and cnsn canadian national seismic network broadband arrays we obtain a 1 d shear model with a 200 km thick d layer with a 3 velocity jump at the top and a negative gradient within the layer from broadband waveform modelling of sh polarized s scs and scd the shear structure above d is similar to the preliminary reference earth model prem dziewonski and anderson 1981 preliminary reference earth model physics of earth planetary interiors 25 297 356 in terms of dt d and s sks differential times sv synthetics for this model assuming a prem core produce a satisfactory fit to the data except at the larger ranges to the north where the waveforms display rapid variation this feature is indicative of lateral variation of the type suggested by grand 1994 where the discontinuity becomes less well defined synthetics computed for a simplified 2 d cross section through this structure produce the scd phase and simple s at larger distances while scd is easily observed in the shear wave data there is little evidence of its counterpart in the p data by testing several models with different p velocity jumps at the same depth as the d jump in shear structure we conclude that the velocity jump must be less than 1 in fact prem provides an excellent fit both in timing and waveform shapes and therefore we conclude that lower mantle structure beneath central america shows clear evidence for a discontinuity in s velocity but not in p

the evolution of hurricane humberto 2001 abstractin 2001 the national oceanic and atmospheric administration and the national aeronautical and space administration marshaled their resources to sample hurricane humberto for 3 successive days during the fourth convection and moisture experiment camex 4 humberto developed from a tropical storm into a category 2 hurricane despite the deep layer vertical shear of the environmental horizontal wind vws increasing markedly on the second and third days of sampling as exhibited in earlier studies the eyewall convection developed an azimuthal wavenumber 1 n 1 asymmetry as the vws increased horizontal divergence and vertical stability within 100 km of the eye exhibited persistent relationships to the vws vector the warm core evolved in an unexpected way the warm anomaly was initially located in the lower troposphere and built upward as the storm intensified the maximum temperature anomaly remained in the lower troposphere on all 3 days while the development of the upper tropospheric warm anom

mesoscale vertical motions near nocturnal convection initiation in pecan abstractradiosonde measurements from the plains elevated convection at night pecan 2015 field campaign are used to diagnose mesoscale vertical motions near nocturnal convection initiation ci these ci events occur in distinctly different environments including ones with 1 strong forcing for ascent associated with a synoptic cold front and midtropospheric short wave 2 nocturnal low level jets interacting with weaker quasi stationary fronts or 3 the absence of a surface front or boundary altogether radiosonde derived vertical motion profiles in each of these ci environments are characterized by low to midtropospheric ascent the representativeness of these vertical motion profiles is supported by distributions of corresponding mesoscale averages from model produced 0 6 h ensemble forecasts thermodynamic data from radiosondes are then analyzed along with selected model ensemble members to elucidate the role of the vertical motions on subsequent ci in a case with strong forcing for mesoscale asce

thermodynamic variability within the convective boundary layer due to horizontal convective rolls abstract data from the convection and precipitation electrification cape experiment conducted during the summer of 1991 are used to examine and quantify the horizontal variability of temperature and moisture within the convective boundary layer cbl potential temperature variations were only about 0 5 k while variations in water vapor mixing ratio values of 1 5 2 5 g kg 1 were observed throughout the cbl using radar aircraft and sounding data it is shown that horizontal convective rolls are the likely cause of these variabilities the enhanced moisture occurred within the roll updraft regions thus rolls were transporting moist air from the surface upward the observed cloud base heights obtained from cloud photogrammetry were produced from the highest moisture values within the roll updraft regions since the roll ascending branches contained moisture values that were most representative of the observed cloud base heights it is likely that measurements from within the roll updrafts would prov

lower mantle seismic discontinuities and the thermal morphology of subducted slabs abstract the nature of the lowermost few 100 km of the mantle holds insights into the scale of convection of the earth s mantle here we investigate the fine structure of this region using seismic migration of shear waves reflecting from velocity discontinuities near the core mantle boundary cmb recorded by a dense network of european seismic stations two main features are found one structure exhibits large scale topography and can be explained by a sharp increase in seismic velocity 206 316 km above the cmb the second structure lies 55 85 km above the cmb and marks a sharp reduction in velocity to explain the origin of these discontinuities we appeal to numerical simulations of three dimensional 3d mantle convection incorporating rigidly moving plates the plates organize the convective flow to allow for the development of large convection cells and cool sheet like downwellings at a convergent plate boundary the results suggest that in places observed seismic complexity in d discontinuity structure may be due to the thermal gradients resulting from the accumulation of cool subducted plate material at the cmb

new insights into the p and s wave velocity structure of the d discontinuity beneath the cocos plate summary broad band p and s waves from earthquakes in south america recorded at californian network stations are analysed to image lateral variations of the d discontinuity beneath the cocos plate we apply two array processing methods to the data set a simplified migration method to the p wave data set and a double array method to both the p and s wave data sets allowing us to compare results from the two methods the double array method images a dipping reflector at a depth range from 2650 to 2700 km in the southern part of the study area we observe a step like topography of 100 km to a shallower reflector at about 2600 km depth to the north as well as evidence for a second deeper reflector at a depth range from 2700 to 2750 km in the north results from the simplified migration agree well with those from the double array method similarly locating a large step in reflector depth in a similar location about 2650 km depth in the south and about 2550 km in the north as well as the additional deeper reflector at the depth of about 2750 km in the north waveform modelling of the reflected waves from both methods suggests a positive velocity contrast for s waves but a negative velocity contrast for p waves for the upper reflector in agreement with predictions from mineral physical calculations for a post perovskite phase transition the data also show some evidence for the existence of another deeper reflector that could indicate a double intersection of the geotherm with the post perovskite stability field that is the back transformation of post perovskite to perovskite close to the core mantle boundary

paleoclimatic records of late triassic paleosols from central ethiopia abstract the present study documents the major paleosols types within the lower adigrat sandstone in the blue nile basin of central ethiopia with the aim of unraveling the paleoclimatic signatures embedded in them the paleosols developed within an 80 m thick siliciclastic succession deposited in a mixed tide and wave dominated incised valley estuary during the late triassic based on down profile variations in pedogenic features three major paleosol types i e types i ii and iii were identified type i paleosols dominate the lower part of the section and are interpreted as moderately well drained argillic vertisols the dominant pedogenic process was shrinking and swelling of expandable clays i e smectite through repeated wetting and drying cycles the morphologies and the mineralogy of the paleosols provide persuasive evidence for pedogenesis under semi arid subtropical climatic conditions with pronounced wet dry seasonality highly fluctuating soil moisture regime and deep groundwater table the presence of a calcic bk horizon deep in the profiles is consistent with elevated soil moisture deficits and low to moderate mean annual precipitation map type ii paleosols interpreted to represent vertic gleysols are more common in the middle part of the section the pervasive gleying reflects poor soil drainage and a shallow groundwater table where the soil is waterlogged most of the year these paleosols suggest a humid tropical climate characterized by alternating wet dry seasonality but with more wet months per year the top of the unit is dominated by type iii paleosols that represent gleyed oxisols reflecting a more humid equatorial climate marked by wet seasons elevated annual soil moisture content and a high water table the presence of plinthite laterite is in agreement with a wet equatorial climate characterized by extensive chemical weathering and long periods of landscape stability the observed vertical progression in the major paleosol types from vertsols to gleysols and oxisols implies a systematic change in the number of wet months most probably in response to regional tectonics and long term climate change because the number of wet months is in part related to latitude and monsoonal climates the upward stratigraphic trend in paleosol orders is interpreted to signal the northward or equatorward migration of the blue nile basin and central ethiopia within pangea from dry subtropical low latitudes in the early late triassic carnian norian toward the humid wet equatorial possibly monsoonal paleoclimatic zone in the late triassic norian rhaetian

bioturbation by symbiont bearing annelids in near anoxic sediments implications for biofacies models and paleo oxygen assessments anoxic or nearly anoxic conditions 4 m o2 have long been associated with the absence of bioturbation and animal traces this premise has guided interpretation of paleoceanographic conditions from rocks and sediments we recently observed a high density living assemblage of highly mobile symbiont bearing burrowing phallodrilinid oligochaetes within a nearly anoxic basin 1 m o2 0 02 0 03 ml l 1 on the peru margin 305 m these observations were made during the most intense part of the 1997 98 el nino when there may have been slight oxygenation of an otherwise anoxic basin but oligochaete presence prior to this event is likely the occurrence of symbiont bearing gutless oligochaetes mainly within the upper 5 cm of the sediment column coincided with a bioturbated zone overlying distinctly laminated sediments our observations redefine the lower oxygen limit of macrofaunal bioturbation to 2 m and indicate a need to modify currently accepted ideas about the relationship between bioturbation and paleo oxygen concentration these results also address an ongoing debate about the lifestyles of bioturbating organisms in oxygen poor settings

seismic evidence links the subducted mongol okhotsk slab to deformation in d near the northeastern margin of the perm anomaly abstract numerical simulations have indicated that the large low shear velocity provinces llsvps dynamically interact with subducted slabs in d and slabs in turn play an important role in influencing the shape and location of the llsvps in this study we find evidence for the existence of the d discontinuity near the northeastern margin of the perm anomaly a smaller llsvp beneath eurasia by analyzing the scd the lower mantle triplication phases generated from two deep events occurring in the northwestern pacific subduction zone and recorded at stations in europe and turkey the d discontinuity in the north is characterized with a 2 velocity increase occurring at a height of 300 km above the core mantle boundary cmb whereas the discontinuity in the south is characterized with a 3 velocity increase occurring at a height of 260 km above the cmb the d discontinuity is most likely attributed to a phase transition from perovskite to post perovskite in conjunction with the presence of relic slab materials likely related to the subducted mongol okhotsk slab our observations along with previous seismic anisotropic detections provide a clue to dynamically link the subducted slab to deformation taking place near the edges of the llsvp

on the characteristic height scales of the hurricane boundary layer in this study data from 794 gps dropsondes deployed by research aircraft in 13 hurricanes are analyzed to studythecharacteristicheightscalesofthehurricaneboundarylayer theheightscalesaredefinedinavariety of ways the height of the maximum total wind speed the inflow layer depth and the mixed layer depth the height of the maximumwind speed and the inflow layerdepth are referred to asthe dynamical boundarylayer heights while the mixed layer depth is referred to as the thermodynamical boundary layer height the data analyses show that there is a clear separation of the thermodynamical and dynamical boundary layer heights consistent with previous studies on the boundary layer structure in individual storms the dynamical boundary layer height is found to decrease with decreasing radius to the storm center the thermodynamic boundary layer height which is much shallower than the dynamical boundary layer height is also found to decrease with decreasing radius to the storm center the results also suggest that using the traditional critical richardson number method to determine the boundary layer height may not accurately reproduce the height scale of the hurricane boundary layer these different height scales reveal the complexity of the hurricane boundary layer structure that should be captured in hurricane model simulations

asymmetric hurricane boundary layer structure from dropsonde composites in relation to the environmental vertical wind shear this study investigates the asymmetric structure of the hurricane boundary layer in relation to the environmentalverticalwind shearin theinner core region data from1878 gps dropsondesdeployed by research aircraft in 19 hurricanes are analyzed in a composite framework kinematic structure analyses based on doppler radar data from 75 flights are compared with the dropsonde composites shear relative quadrantmeancomposite analysesshow that boththekinematicandthermodynamic boundarylayerheight scalestend to decrease with decreasing radius consistent with previous axisymmetric analyses there is still a clear separation between the kinematic and thermodynamic boundary layer heights both the thermodynamic mixed layer and height of maximum tangential wind speed are within the inflow layer the inflow layer depth is found to be deeper in quadrants downshear with the downshear right dr quadrant being the deepest the mixed layer depth and height of maximum tangential wind speed are alike at the eyewall but are deeper outside in quadrants left of the shear the results also suggest that air parcels acquire equivalent potential temperature ue from surface fluxes as they rotate through the upshear right ur quadrant from the upshear left ul quadrant convection is triggered in the dr quadrant in the presence of asymmetric mesoscale lifting coincident with a maximum in ue energy is then released by latent heating in the downshear left dl quadrant convective downdrafts bring down cool and dry air to the surface and lower ue again in the dl and ul quadrants this cycling process may be directly tied to shear induced asymmetry of convection in hurricanes

high temperature anomalies oceanward of subducting slabs at the 410 km discontinuity abstract our p wave whole mantle tomography revealed a low velocity region oceanward of the northern honshu slab of the pacific plate at depths around the 410 km seismic discontinuity resolution tests and scrutiny of the traveltime residuals for the ray paths passing through the low velocity region indicate that this anomaly is a resolvable feature and not an artifact due to the strong slab anomalies the existence of the slow anomalies is also supported by the analysis of the p wave records from the j array a large aperture seismic array in japan for a bonin earthquake the p arrivals to northern honshu at epicentral distances of 13 20 are strongly triplicated because of the 410 km discontinuity the later arrivals along the retrograde branch where ray paths pass through the low velocity region are anomalously slow comparison of the observed and synthetic waveforms indicates not only slow anomalies but also depression of the 410 km discontinuity this depression represents the direct evidence for the low velocity zone of primarily thermal origin an excess temperature of 200 k and the associated fractional melt of less than 1 can explain both the results of the tomographic and waveform analyses

convective structure of hurricanes as revealed by lightning locations cloud to ground lightning flash locations were examined for nine atlantic basin hurricanes using data from the national lightning detection network a common radial distribution in ground flash density was evident a weak maximum in the eyewall region a clear minimum 80 100 km outside the eyewall and a strong maximum in the vicinity of outer rainbands 210 290 km radius these results are consistent with the authors previous study of hurricane andrew none of the storms showed this characteristic radial structure during prehurricane stages the results support the division of precipitation in the hurricane into three distinct regimes the eyewall is a unique phenomenon but shares some attributes with deep weakly electrified oceanic monsoonal convection the region outside the eyewall and under the central dense overcast has characteristics of the trailing stratiform region of mesoscale convective systems including a relatively high fraction of positive polarity flashes the outer bands with mean maximum flash density at the 250 km radius contain the vast majority of ground flashes in the storms eyewall lightning defined as that within 40 km of the center was examined for four moderate to strong hurricanes such lightning occurred episodically during hurricane stage with 93 of hourly intervals containing no detected flashes eyewall lightning outbreaks over water always occurred at the beginning of or during times of intensification but often were indicative of the imminent end of deepening it is proposed that the existence of such inner core lightning might reveal the presence of an eyewall cycle for the one storm with available aircraft reconnaissance data eyewall cycles were reliably identified by the occurrence of inner core lightning and inner core lightning appeared only during such cycles suggestions are made as to how eyewall flashes in existing hurricanes might be used to help predict hurricane intensity change

the structure of the atmospheric boundary layer in the central equatorial pacific during january and february of fgge abstract the structure of the atmospheric boundary layer for a region between hawaii and the equator is studied using dropwindsonde data 900 soundings collected in january and february 1979 as part of the first garp global experiment these data were used to establish the longitudinal and latitudinal variations in the thermodynamic and wind structure of the boundary layer and describe differences in the structure for convectively active and inactive conditions low level inversions at a pressure of approximately 850 mb were found to be an important feature of the structure of the boundary layer for undisturbed conditions although the frequency of low level inversions decreased equatorward from hawaii the average height of the inversions observed in these regions did not vary significantly in the north south direction for convectively undisturbed conditions low level inversions are on the average of sufficient strength to suppress deep convection however it is shown they could easily be modified

a hurricane morphology and sea surface wind vector estimation model based on c band cross polarization sar imagery over the last decades data from spaceborne synthetic aperture radar sar have been used in hurricane research however some issues remain when wind is at hurricane strength the wind speed retrievals from single polarization sar may have errors because the backscatter signal may experience saturation and become double valued by comparison wind direction retrievals from cross polarization sar are not possible until now in this paper we develop a 2 d model the symmetric hurricane estimates for wind shew model and combine it with the modified inflow angle model to detect hurricane morphology and estimate the wind vector field imaged by cross polarization sar by fitting shew to the sar derived hurricane wind speed we find the initial closest elliptical symmetrical wind speed fields hurricane center location major and minor axes the azimuthal orientation angle relative to the reference ellipse and maximum wind speed this set of hurricane morphology parameters along with the speed of hurricane motion are input to the inflow angle model modified with an ellipse shaped eye to derive the hurricane wind direction a total of 14 radarsat 2 scansar images are employed to tune the combined model two sar images acquired over hurricane arthur 2014 and hurricane earl 2010 are used to validate this model comparisons between the modeled surface wind vector and measurements from airborne stepped frequency microwave radiometer and dropwindsondes show excellent agreement the proposed method works well in areas with significant radar attenuation by precipitation

the postperovskite transition the discovery of the postperovskite ppv transition has profound impact on our understanding of the core mantle boundary cmb region unlike perovskite pv the ppv phase has a layered structure of the sio6 octahedra which may lead to a large contrast in some properties with pv recent studies have proposed unusual properties of ppv such as a large positive clapeyron slope a large sensitivity of the transition depth to iron a decrease in bulk sound speed at the transition and a development of significant lattice preferred orientation many of the proposed properties can provide explanations for the intriguing seismic observations at the cmb region yet significant discrepancies still exist however rapid developments in mineral physics will continue to improve our knowledge on the changes across the ppv transition

low level kinematic thermodynamic and reflectivity fields associated with hurricane bonnie 1998 at landfall during 11 h on 26 august 1998 two noaa wp 3d aircraft deployed 85 global positioning system gps dropwindsondes within 2 of latitude of the circulation center of hurricane bonnie as it made landfall in north carolina about 75 of the sondes successfully collected data which were used to create a series of storm relative horizontal maps of kinematic and thermodynamic variables from 10 m to 2 km reflectivity fields were analyzed from the weather surveillance radar 1988 dopplers wsr 88ds located at wilmington and morehead city north carolina and the tail and lower fuselage radars aboard the wp 3ds gps sonde performance and deployment spacing is adequate to identify several aspects of the vortex these include 1 warm dry stable air in the offshore flow that results in reduced equivalent potential temperatures entering the southern portion of the eyewall 2 cooler air collocated with the upwelled water in the right rear quadrant and under the eyewall and 3 an atypical radial wind pattern with strong inflow southwest of the circulation center and outflow northeast of the center the strongly asymmetric structure found at 10 m becomes much more homogeneous by 2 km altitude no intense rainbands developed over land in the onshore flow nor did the bands in the onshore flow undergo any significant changes once they made landfall beyond the eyewall the offshore flow contained much less precipitation than the onshore portion of the storm characteristics beyond the eyewall appear to have been modulated by the proximity to land but hurricane intensity did not vary the authors infer that the lower energy content of the inflow was offset by the contraction of the eyewall

taphonomic analysis of fish in rift lacustrine systems environmental indicators and implications for fish speciation abstract two rift basin lacustrine successions cacheuta and los rastros formations in the middle triassic of argentina were studied to test two different hypotheses 1 fish taphonomy is useful as an indicator of environmental conditions for these two paleolakes and 2 fish taphonomy is useful for understanding environmental effects on speciation the fish fossils are found in two lacustrine deposits as isolated and disarticulated scales and cranial bones clumps and stringers of scales articulated body segments and complete specimens four taphofacies are defined for cacheuta specimens ca a to ca d and three taphofacies are defined for los rastros fish assemblages lr a to lr c a principal components analysis was performed with the taphonomic features supporting the seven taphofacies defined a taphonomic model is proposed that characterizes a lacustrine deltaic environment developed in the rift basin and identifies three sub environments each one with its particular fossil assemblages the fish assemblages in the los rastros formation suggest that the fishes preserved in delta front and turbidity current deposits lr b and lr c taphofacies were allochthonous to the lake and probably inhabited the delta plains and affluent fluvial system in contrast the isolated fish remains preserved in open lake deposits lr a taphofacies likely represent both autochthonous and or allochthonous specimens in the cacheuta formation articulated and isolated fish remains preserved in open lake deposits ca a and ca d tafofacies might represent autochthonous lacustrine specimens based on the good preservation of the material the fish remains preserved in underflow and turbidity current deposits ca b and ca c taphofacies were allochthonous to the lake and probably inhabited the delta plain and affluent fluvial system the fish taphonomic study of two different rift basin lacustrine successions allows test of the two proposed hypotheses fish taphonomy was useful as an indicator of environmental conditions beacuse the differences in fish preservation allowed differentiation of the sub environments and reconstruction of the environmental conditions and dynamics of the rift lake basins also fish taphonomy was useful for understanding environmental effects on speciation by characterizing the environments and dynamics that promote the development of new fish species recognizing fish inhabited environments and identifying the generalist and specialist species

boundary layer structure and dynamics in outer hurricane rainbands part i mesoscale rainfall and kinematic structure abstract results of hurricane boundary layer experiments conducted in outer rainbands of hurricanes josephine 1984 and earl 1986 are presented comparisons of precipitation and kinematic structures in these storms and in hurricane floyd 1981 indicate that principal rainbands have common characteristic mesoscale and convective scale features in the boundary layer the two dimensional mesoscale structure suggests that these rainbands are made up of a linear aggregate of cellular reflectivity elements on the inner upshear side of the band and stratiform rain on the outer downshear side the bands are oriented perpendicular to the shear above the boundary layer and cells move downband at about 85 of the density weighted mean wind speed of the 0 2 6 km layer the boundary layer wind field is strongly influenced by the rainband with alongband and crossband wind maxima located on the outer side of the band axis and minima 4 8 km to the inner side maximum crossband convergence and cyclonic shear vor

a review of the middle late pennsylvanian west european regional substages and floral biozones and their correlation to the geological time scale based on new u pb ages abstract lower moscovian duckmantian to lower asselian ash beds in the continental basins of the central and western czech republic have yielded 15 new high precision u pb single crystal zircon ca id tims ages these are used to improve the calibration of the west european regional terrestrial stages and their correlation to the geological time scale they also allow an improved correlation between the macrofloral biozones that are used for biostratigraphy in the european pennsylvanian coalfields the marine biozones on which the global geological time scale was partly established and the fresh water and terrestrial faunal biozones most of the floral biozones have proved to be essentially isochronous although the ranges of some individual but stratigraphically important taxa may differ between basins

a lower mantle s wave triplication and the shear velocity structure of d summary a lower mantle s wave triplication detected with short and longperiod wwssn and csn recordings indicates a substantial shear velocity discontinuity near 280 km above the core mantle boundary the triplication can be observed in rotated sh seismograms from intermediate and deep focus events throughout the distance range from 70 to 95 three distinct source region receiver array combinations that have been investigated in detail demonstrate consistent travel time and relative amplitude behaviour of the triplication with slight systematic shifts in the triplication indicating up to 40km variations in the depth of the discontinuity modelling of the observations with synthetic seismograms produced with the cagniard de hoop and reflectivity methods constrains the shear velocity increase to be 2 75 k 0 25 per cent comparable to upper mantle discontinuities short period observations indicate that the velocity increase may be a sharp first order discontinuity or may extend over a transition zone no more than 50 km thick the shear velocity gradient below the discontinuity within the d layer is not well constrained by the sh data but slightly positive or near zero velocity gradients are consistent with the long period amplitude ratios of scsh sh

geographic boundary and shear wave velocity structure of the pacific anomaly near the core mantle boundary beneath western pacific we determine the geographical boundary and shear velocity structure of a very low velocity province at the base of the earth s mantle beneath western pacific we term it the pacific anomaly based on the waveform modeling and travel time analysis of scsh sh phases our seismic data are from the china national digital seismographic network the f net in japan the global seismographic network and several passcal arrays the observed scs sh differential travel time residuals allow the northwestern geographic boundary of the anomaly to be clearly defined the seismic data also suggest that the average shearvelocity reduction inside the anomaly reaches 5 in the lowermost 300km of the mantle waveform modeling of the seismic data sampling the edge of the anomaly suggests that the northwestern boundary is best characterized by a shear velocity model with a velocity jump of about 2 at about 100 145km above the core mantle boundary and a thin 30 km thick basal layer with a shear wave velocity reduction of 13 stacked seismic data sampling the middle of the anomaly however show no evidence for any internal discontinuity with a velocity decrease greater than 2 in the middle of the anomaly overall the seismic data sampling the base of the pacific anomaly can be explained by a negative shear velocity gradient from 0 to 1 top to 13 bottom in the lowermost 220 km of the mantle similar to those of a very low velocity province beneath the south atlantic ocean and the indian ocean such a strong negative shear velocity gradient can be explained by partial melting of a compositional anomaly produced early in the earth s history located within a bottom thermal boundary layer our travel time data also exhibit small scale variations inside the anomaly indicating existence of internal small scale seismic heterogeneities inside the pacific anomaly

typhoon kinematic and thermodynamic boundary layer structure from dropsonde composites the data from 438 global positioning system dropsondes in six typhoons are analyzed to investigate the mean atmospheric boundary layer structure in a composite framework following a recent study on boundary layer height in atlantic hurricanes we aim to quantify characteristics of boundary layer height scales in western pacific typhoons including the inflow layer depth hinflow height of the maximum tangential wind speed hvtmax and thermodynamic mixed layer depth in addition the kinematic and thermodynamic boundary layer structures are compared between the dropsonde composites using data in typhoons and hurricanes our results show that similar to the hurricane composite there is a separation between the kinematic and thermodynamic boundary layer heights in typhoons with the thermodynamic boundary layer depth being much smaller than hinflow and hvtmax in the typhoon boundary layer all three boundary layer height scales tend to decrease toward the storm center our results confirm that the conceptual model of zhang et al 2011a for boundary layer height variation is applicable to typhoon conditions the kinematic boundary layer structure is generally similar between the typhoon and hurricane composites but the typhoon composite shows a deeper inflow layer outside the eyewall than the hurricane composite the thermodynamic structure of the typhoon boundary layer composite is warmer and moister outside the radius of maximum wind speed than the hurricane composite this difference is attributed to different environmental conditions associated with typhoons compared to the hurricanes studied here

hurricane sea surface inflow angle and an observation based parametric model abstractthis study presents an analysis of near surface 10 m inflow angles using wind vector data from over 1600 quality controlled global positioning system dropwindsondes deployed by aircraft on 187 flights into 18 hurricanes the mean inflow angle in hurricanes is found to be 22 6 2 2 95 confidence composite analysis results indicate little dependence of storm relative axisymmetric inflow angle on local surface wind speed and a weak but statistically significant dependence on the radial distance from the storm center a small but statistically significant dependence of the axisymmetric inflow angle on storm intensity is also found especially well outside the eyewall by compositing observations according to radial and azimuthal location relative to storm motion direction significant inflow angle asymmetries are found to depend on storm motion speed although a large amount of unexplained variability remains generally the largest storm relative inflow angles 50 are found in the fas

why rolls are prevalent in the hurricane boundary layer recent remote sensing observations show that the hurricane boundary layer flow although energetic is not a region of homogeneous turbulence in fact the observations convincingly demonstrate that a large fraction of the turbulent flow in the regions away from the deep convective rainbands is highly organized into intense horizontal roll vortices that are approximately aligned with the mean wind and span the depth of the boundary layer these observations show that rolls strongly increase the flux of momentum between the underlying surface and the main body of the storm compared to an equivalent hurricane boundary layer flow without rolls the linear and nonlinear dynamics of hurricane boundary layer roll formation are outlined and it is shown why rolls are in fact the expected basic hurricane boundary layer state the model presented here explains the hurricane roll features currently documented in field programs and makes predictions that can be tested in future experiments the primary effects of rolls on the boundary layer fluxes are inherently nonlocal and nongradient and hence cannot be captured by standard downgradient turbulence parameterizations used in hurricane simulations however the nonlinear theory is the proper starting point for developing boundary layer parameterizations that include roll modification of the turbulent fluxes

middle moscovian climate of eastern equatorial pangea recorded in paleosols and fluvial architecture abstract fluvial architecture in conjunction with the morphology petrographical mineralogical and geochemical composition of intercalated paleosols of the middle moscovian upper radnice member of the continental kladno rakovnik basin czech republic were studied in order to decipher climatic signals in the eastern pangea region during the late paleozoic ice age analysis of architectural elements reveals vertical changes from strongly amalgamated channel fills of bedload dominated braided streams to isolated ribbon like meandering channel fills in mud dominated floodplain strata the resulting large scale fining upward cycles separated by laterally widespread bounding surfaces are interpreted as having been formed in response to allocyclic processes driven by variable intensities of precipitation which affected the density of vegetation cover across the landscape and in turn the amount and character of sediment supply bedload dominated parts of the cycles were deposited during periods of low water tables and sparse vegetation whereas periods of maximum precipitation resulted in higher water tables and a greater density of vegetation cover which in turn stabilized the floodplains and fixed streams to narrow meandering anastomosing channels in mud dominated floodplain strata associated paleosols resemble modern vertisols which form under seasonal precipitation in modern settings however coeval formation of inertinite rich peat represented by histosols and gleyed low chroma vertisols in the stratigraphically lowest paleosol succession occurred under overlapping marginal conditions for the climatically different types of soils i e under a seasonal climate where precipitation exceeds evapotranspiration for 6 to 8 months out of the year mean annual precipitation calculated from the geochemistry of b horizons of vertisols calmag proxy varies between 1815 and 1730 mm yr

vertical structure of the tropical boundary layer abstract obsemations presented show that the undisturbed subcloud layer near the itcz resembles that of the trades mixed and transition layers are also seen between cloud drafts during disturbed periods when shallow mixed layers 200 m can persist for several hours modification of the lower atmosphere during disturbed periods is most marked in the lowest 1200 m mixed layers are observed during prolonged disturbed periods disturbed mixed layers are shallower and cooler than undisturbed ones light and moderate rainfall events moisten the mixed layer but mixed layers in the environment around strong rainfall are drier it is hypothesized that that the effect of a number of downdrafts spreading laterally produces the mixed layer cooling and drying observed changes of mixed layer structure with stability measured by the ratio of mixed layer height to the monin obukhov length are presented

why is the tropical cyclone boundary layer not well mixed abstractplausible diagnostics for the top of the tropical cyclone boundary layer include i the top of the layer of strong frictional inflow and ii the top of the well mixed layer that is the layer over which potential temperature is approximately constant observations show that these two candidate definitions give markedly different results in practice with the inflow layer being roughly twice the depth of the layer of nearly constant here the authors will present an analysis of the thermodynamics of the tropical cyclone boundary layer derived from an axisymmetric model the authors show that the marked dry static stability in the upper part of the inflow layer is due largely to diabatic effects the radial wind varies strongly with height and therefore so does radial advection of this process also stabilizes the boundary layer but to a lesser degree than diabatic effects the authors also show that this differential radial advection contributes to the observed superadiabatic layer ad

palaeoecology of the triassic black shale bivalve daonella new insights into an old controversy abstract several modes of life have been proposed for bivalves of the genus daonella taphonomic studies revealed that most taphocoenoses containing lumachellas shellbeds and butterflied preserved specimens are allochthonous articulated specimens with closed valves and well orientated sagittal planes are interpreted to be in situ autochthonous assemblages show a population structure dominated by subadults and adults monospecific and paucispecific taphocoenoses with daonellids are not due to preservational biases but reflect the former biocoenoses most species show a dependence on facies some are restricted to dysoxic milieus others are only known from normoxic facies but all preferred soft soupy sediments morphological examination does not support the presence of byssus gland in adult stages of daonellids which suggests that they could not be attached to floats proposed life habits such as semi infaunal mud stickers epibenthic chemosymbionts holonekton holoplankton or byssal attached pseudoplankton conflict with taphonomical constraints distribution and morphology daonellids are herein interpreted as epibethic pleurothetic bivalves showing adaptive features to dysoxic milieus like subcircular flat thin shelled valves daonellids were well adapted to soft soupy substrates the use of lighter calcite in place of aragonite the thin shell and the general form of the shell qualified them to float on soft sediments snow shoe strategists

influence of station topography and moho depth on the mislocation vectors for the kyrgyz broadband seismic network knet deviations of slowness and backazimuth from theoretically calculated values the so called mislocation vectors are measured for the kyrgyz broadband seismic network knet in the tien shan region 870 events have been analysed for arrivals of p and pkp waves from all azimuths the deviations of slowness and backazimuth show a strong trend with values up to 1 s deg 1 for slowness values for waves arriving from the north and south and backazimuth deviations of in some cases more than 10 degrees for waves arriving from the east and west calculating the traveltime deviations of the stations for topography of the tien shan region and moho depth values appropriate for this area shows that most slowness and backazimuth deviations can be reduced to very small values the remaining mislocation vectors show no strong trends and are on average smaller than 0 2 s deg 1 for slowness and 2 degrees for backazimuth values which is within the error bars of these measurements results from array methods that rely on the knowledge of the backazimuth values show much improved resolution after the correction of the mislocation vectors which shows the importance of knowing and correcting for structures directly beneath arrays

low level inversions over the tropical pacific thermodynamic structure of the boundary layer and the above inversion moisture structure abstract the structure of the boundary layer over a broad region of the equatorial pacific is studied using dropwinsonde measurements made in january february may and june of 1979 low level inversions of sufficient strength to inhibit deep convection are found to be present in more than 50 of the soundings these inversions appear to play a critical role in regulating convective activity over the central and eastern pacific the tops of the inversions have an average pressure level of approximately 300 mb and show little latitudinal or longitudinal variation the majority of the inversion soundings approximately 70 have a reversal in the mixing ratio profile qreversal above the inversion that appears as a dry layer at the top of the inversion layer capped by a relatively moist layer this moist layer is on the average 2 g kg 1 more moist than the corresponding soundings that have no qreversal no systematic regional or temporal variations in the frequency of occurrence of the qreversal or the str

eye excess energy and the rapid intensification of hurricane lili 2002 abstract over 4 5 days noaa and u s air force personnel in reconnaissance aircraft deployed 44 global positioning system dropwindsondes gps sondes in the eye of hurricane lili 2002 the vertical profiles derived from these gps sondes were used to determine the evolution of the height of the inversion presence and height of the hub cloud the height of the lifted condensation layer and the depth of the mixed layer as lili deepened underwent rapid intensification ri and eventually rapid decay the lower portion of the eye moistened and the lapse rate became moist adiabatic the inversion layer rose as lili intensified and then quickly fell over 1500 m at the beginning of ri comparison of the equivalent potential temperature e of the eye with that in the eyewall revealed that like many other hurricanes the eye was a reservoir for the warmest e the authors define a variable called eye excess energy that is a function of the difference in e between the eye and the eyewall and the depth over

slab and height resolving models of the tropical cyclone boundary layer part i comparing the simulations diagnostic models of the tropical cyclone boundary layer have important practical uses including engineering design and climatological risk assessment studies and as components of tropical cyclone potential intensity models a widely used class of such models has been slab models in which the governing equations are depth averaged here a slab model is compared with one that fully resolves height and it is shown that the vertical averaging leads to substantial differences in the simulations the slab model produces excessively strong inflow and too great a departure of the boundary layer mean winds from gradient balance in moving storms the slab models produce much too strong a motion induced asymmetry and can support an asymmetric analogue of the quasi inertial oscillation previously noted in axisymmetric slab models given the considerable impact of the vertical averaging in slab models on the simulated flow in the tropical cyclone boundary layer it is difficult to recommend their further use for applications where quantitative accuracy is important other applications will require care to ensure that the results are not unduly affected by the depth averaging part ii of this article presents a detailed analysis of the reasons for the differences between depth averaged and height resolving simulations of the tropical cyclone boundary layer 2010 published by john wiley sons ltd

miniature supercells in an offshore outer rainband of hurricane ivan 2004 abstract airborne doppler radar observations are used to document the structure of three miniature supercells embedded in an outer rainband of hurricane ivan on 15 september 2004 the cells were located more than 100 km offshore beyond the doppler range of coastal radars the combination of large cape large vertical wind shear and moderate cell relative helicity with an apparent midlevel dry air intrusion provided an offshore environment supporting rotating storms each shallow cell contained a 5 7 km diameter mesocyclonic updraft with midlevel updraft and vorticity maxima that exceeded 6 m s 1 and 0 008 s 1 respectively such offshore structures are consistent with miniature supercells observed onshore in association with tropical cyclone tornado outbreaks the strong updrafts resulted from a combination of kinematic convergence thermal instability and shear induced vertical perturbation pressure gradients mesocyclone production largely resulted from the tilting and subsequent stretching of low l

comparing ray theoretical and finite frequency teleseismic traveltimes implications for constraining the ratio of s wave to p wave velocity variations in the lower mantle

the fate of slabs inferred from seismic tomography and 130 million years of subduction the volume and location of subducted plate since 130 ma are reconstructed from magnetic anomalies and updated finite rotation parameters describing relative motions in the ocean basins and between plates and hotspots the area of subducted plate is calculated from the relative motions between overriding and overridden plates along the length of convergence in the hotspot reference frame in 5 ma intervals ridge locations are reconstructed by rotating magnetic anomalies from their present to their former positions the distances between trenches and ridges at a certain point of time in the spreading direction are thus estimated and are used to determine the ages of trenches according to the spreading history recorded in present day oceans the thickness of the oceanic plate is obtained from the age based on the half space cooling model about 3 45 10 10 km 3 of oceanic plate has been subducted during the past 130 ma with maximum accumulation beneath southeast eurasia at spherical harmonic degree l 2 where subduction flux peaks excellent correlation is found between four seismic tomographic models at the top of the lower mantle about 800 1100 km deep and predicted slab locations for some seismic models excellent correlation is also found at other degrees in that depth range some models also have good correlations with predicted slab locations in the deep mantle at l 2 direct comparison between subduction and seismic tomographic patterns at 800 1100 km shows that subduction history correlates with tomography very well in terms of location and amplitude of anomalies cold downwellings which may be related to slabs appear to be trapped in the mesosphere or middle mantle correlations between seismic tomography and subduction over different time periods support this conclusion there are also some correlations in the upper mantle and in the deep lower mantle although they are generally not as significant as those in the 800 1100 km depth range there may be a significant boundary in the mantle near the 800 1100 km depth from a geodynamic and chemical point of view the lower mantle may start at a depth closer to 1000 km than to 670 km

the inflow to tropical cyclone humberto 2001 as viewed with azimuth height surfaces over three days abstractthe deployment of 228 global positioning system dropwindsondes gps sondes over three consecutive days in tropical cyclone humberto 2001 allows for the creation of azimuth height z surfaces from sea level to 3 km altitude at 0 25 and 0 5 latitude distance from the storm center the authors estimate the radial flow along these z surfaces to diagnose the mass flux through said surfaces as humberto deepens from 1000 to 983 hpa from the first to the second day then fills to 992 hpa by the third day as the tropical cyclone tc intensifies the width depth and rate of inflow increase the inflow remains a wavenumber 1 pattern throughout the three days the center of the inflow rotates clockwise over this period following the expected forcing due to both the tropical cyclone motion and deep layer shear vectors net vertical mass flux based on continuity within a given volume is correlated with tc intensity only for the inner 0 25 z surface slightly farther from the center at 0 5

postperovskite phase transition and its geophysical implications 1 the stability of mg fe sio3 perovskite in the deep lower mantle has long been uncertain recently a phase transition from perovskite to postperovskite was discovered through a significant change in the x ray diffraction pattern at high pressure and high temperature conditions corresponding to the core mantle boundary region this phase transition was also confirmed by first principles calculations these suggest that mg fe sio3 postperovskite is the predominant mineral in the lowermost mantle called the d layer and phase transition from perovskite to postperovskite has significant geophysical implications for its nature and dynamics the postperovskite phase may account for the large seismic anomalies observed in the d region such as the d discontinuity s wave anisotropy and anticorrelation between the anomalies in s wave and bulk sound velocities in addition this phase transition is a strongly exothermic reaction it destabilizes the thermal boundary layer at the base of the mantle and should promote the formation of high temperature upwelling plumes

the mechanism and predictability of an elevated convection initiation event in a weak lifting environment in central eastern china abstractan elevated convection initiation ci of a quasi linear mesoscale convective system mcs that occurred in a weak lifting environment in the early morning on 23 june 2016 in central easter

convective scale variations in the inner core rainbands of a tropical cyclone airborne doppler radar documented a variety of convective scale structures within the inner core rainbands of hurricane rita 2005 as predicted by past studies wind shear determined azimuthal variations in the convection all convective scale circulations had radial inflow at low levels upward motion and outflow in the midtroposphere convective cells at smaller radii contained a low level tangential jet determined largely by tangential acceleration due to angular momentum conservation uy r term while cells at larger radii contained a low level and or midlevel jet determined jointly by the uy r and vertical advection terms the outflow was at a higher lower altitude for the outer inner cells radial variations in the convective cells are attributable to differencesin buoyancy and vertical shear of the radial wind u z more buoyant updrafts at larger radii enhance vertical advection of y creating local tangential jets at midlevels at smaller radii the stronger low level radial inflow contributes to a greater u z confining convectively generated jets to low levels the low level tangential jet and convectively generated pressure gradients produce outward pointing supergradient acceleration that decelerates the boundary layer inflow consequently this supergradient flow will enhance convergence and convection at the radius of inner rainbandcells increasing the likelihoodof secondary eyewall formation it is hypothesized that a critical zone for secondary eyewall formation exists where sufficiently high u z consistently constrains the altitudes of convectively generated supergradient flow so that convection in this radial zone leads to a newly developed eyewall once an incipient secondary eyewall forms at a certain radius subsidence occurring along its inner edge separates it from the primary eyewall

controlled excavations in the pesciara and monte postale sites provide new insights about the palaeoecology and taphonomy of the fish assemblages of the eocene bolca konservat lagerstatte italy abstract the eocene konservat lagerstatte of bolca italy is famous for the abundance and exquisite preservation of its fossils although the bolca sites have provided one of the most studied ichthyofaunistic fossil assemblages of the world several aspects about the community structure and the biostratinomic processes that led to the accumulation of its fish remains have been neglected or underestimated in order to improve our knowledge concerning the palaeoecology and palaeoenvironment of bolca a quantitative palaeoecological and taphonomic analysis of the fish remains collected during controlled excavations at the pesciara and monte postale sites is presented herein the results of these analyses concur to suggest that these two sites have different speciose fish assemblages and different depositional contexts the high quality preservation of the fishes from the pesciara site has allowed for the species level identification of most of its specimens providing a good resolution of its palaeoecological spectrum the pesciara fish assemblage is defined by a sharp oligarchic structure clearly dominated by planktivorous taxa the taphonomic features confirm that the sediments were deposited in an intraplatform basin in which anoxic conditions at the bottom and the development of the biofilm acted as promoters of high quality fossil preservation on the other hand the moderate preservation quality of the fishes from monte postale does not allow for most of the specimens to be identified at the genus or species level making it difficult to interpret the ecological and trophic relationships within this assemblage nevertheless the abundance of marine and terrestrial plants coupled with the large number of invertebrates including abundant corals concur to suggest that the sediments of monte postale were likely deposited close to an emerged coastal area characterized by mangroves seagrass and coral reefs the prominent disgregation of fish skeletons coupled with the unimodal dispersion of the elements and bioturbations clearly indicate a high degree of disturbance in the monte postale palaeoenvironment suggesting at least periodic aerobic conditions at the bottom

atypical thermodynamic profiles in hurricanes the global positioning system dropwindsondes deployed in hurricane bonnie on 26 august 1998 with supporting deployments in hurricanes mitch 1998 and humberto 2001 are used to identify three unusual thermodynamic structures in the lower cloud and subcloud layers two of these structures impact the energy content of the inflow and therefore the intensity of the hurricane first positive lapse rates of equivalent potential temperature are found near the top of the inflow these layers insulate the inflow from the negative impacts of entrainment mixing and promote rapid energy increases especially near the eyewall the second structure is a rapid decrease of equivalent potential temperature adjacent to the sea surface this is essentially a prominent surface layer that owes its existence to both higher moisture content and a superadiabatic lapse rate the steep lapse rate most often occurs under and near the eyewall where wind speeds at the surface exceed hurricane force the author speculates that water loading from spray increases the residence time of air parcels in the surface layer contributing to the creation of this structure the third feature is a moist absolutely unstable layer previously identified by bryan and fritsch for the midlatitudes these layers are found adjacent to the eyewall in rainbands and in the hub cloud within the eye and are evidence of mesoscale or vortex scale convergence and the very modest instabilities often found in the core of a hurricane

p and s wave reflections from anomalies in the lowermost mantle summary seismic p and s waves recorded at the grf array in germany are used to study the inhomogeneous structure of the boundary layer d at the base of the mantle the use of the seismic array allows the detection of small scale anomalies in the lowermost mantle the lateral resolution attainable is about 100 to 400 km i e more than 10 times better than with tomographic methods the analysis of 13 years of grf broad band array data yields 255 events with high signal to noise ratio which are used to map the lowermost mantle 74 of these events show anomalous p waves pdp which arrive 3 6 s after the direct p wave and have a slowness 0 7 0 8 s smaller than the slowness of direct p other events close to the events with pdp do not have such an anomalous phase using slowness traveltime amplitude and waveform information it is demonstrated that pdp is caused by an anomalous lower mantle velocity structure below the turning point of the p wave if the pp phase i e a p wave first reflected at the free surface near the source is used together with the p phase distinct and well sepaarted p velocity anomalies can be determined under the nansen basin the kara sea and northern siberia the areas of the bounce points of pdp in the lower mantle have a lateral extension of about 100 by 200 km but this is not the size of the anomaly since the resolution of p waves at 1 hz in this depth is 130 km by 260 km fresnel zone the accuracy to which the depth of the reflector 2612 km under the nansen basin and 2605 km under northern siberia respectively can be determined for 1 d models is 10 to 20 km the velocity contrast at the lower mantle discontinuity is about 3 per cent 1 to 1 5 per cent areas which have velocity fluctuations smaller than about 1 per cent can not be detected as anomalous areas 2 d models of the anomalies reveal the range of adequate models and possible trade offs if the lateral extension of the anomaly is about 7 the reflector has to be 40 km deeper than in the 1 d model if the dip of the reflector in the lowermost mantle is only about 1 5 it is difficult to resolve if the reflector is tilted towards the source or towards the receiver for the anomaly under the nansen basin deviations from the great circle path are observed for pdp indicating 3 d effects below the three anomalies the core mantle boundary cmb can be located by pcp with a depth in agreement with standard earth models under northern siberia has a region where p and s velocity anomalies coincide but also a region where only an s velocity anomaly but no p velocity anomaly is observed this results in changes of the poisson ratio from 5 9 per cent to 4 8 per cent 1 5 per cent across the discontinuity in the lowermost mantle for the regions studied the analysis of the s waves s sds and scs reveals two s velocity anomalies in the lowermost mantle under northern siberia the first anomaly coincides with the p velocity anomaly under northern siberia and can be explained by a 1 d model with a reflector depth of 2610 km 15 km and a velocity contrast of 2 3 per cent the second s velocity anomaly is in an area where no p velocity anomaly can be detected the corresponding 1 d s velocity model has a reflector depth of 2575 km 15 km and an s velocity contrast of 2 6 per cent the smallest structures that can be resolved with the s waves in this depth are about twice as large as for the p waves i e 230 km by 460 km fresnel zone the joint analysis of p and s waves therefore shows a region with a p velocity anomaly together with weak indications for an s velocity anomaly nansen basin and a second region with a p but no s anomaly kara sea the lowermost mantle

oxygen and hydrogen isotope compositions of paleosol phyllosilicates differential burial histories and determination of middle late pennsylvanian low latitude terrestrial paleotemperatures abstract the clay mineralogy chemistry and stable hydrogen and oxygen isotope compositions were measured from 20 phyllosilicate samples representing 11 pennsylvanian age paleosol profiles taken from three cores in the illinois basin in order to assess their utility as proxies of low latitude terrestrial paleotemperatures the majority of the samples are mineralogical mixtures of illite smectite i s kaolinite and rarely discrete illite samples from a shallowly buried locality in the northern part of the basin are dominantly composed of smectite rich i s with variable amounts of kaolinite and no discrete illite samples from deeply buried interior parts of the basin are composed of illite rich i s variable amounts of kaolinite and discrete illite these phyllosilicate mixtures have 18 o v smow and d v smow values that range from 17 2 to 23 0 and 56 to 27 respectively assuming that the phyllosilicates preserve a record of isotopic equilibrium with pennsylvanian meteoric waters these oxygen and hydrogen isotope values correspond to crystallization temperatures ranging from 22 3 c to 55 3 c the clay mineralogy phyllosilicate 18 o and d values and calculated crystallization temperatures of 44 c to 55 c from deeply buried localities in the interior of the basin are not consistent with a pedogenic origin instead these trends are considered to be the result of diagenetic recrystallization of pedogenic minerals in response to greater depths of burial by 1 5 to 3 km in the southerly basin center localities as well as an interval of middle permian elevated heat flow associated with magmatic intrusions in the southern part of the basin phyllosilicate mineralogy 18 o and d values and calculated phyllosilicate crystallization temperatures from a shallowly buried northern locality in the illinois basin are consistent with a pedogenic origin and reveal a long term warming trend from an average temperature of 23 3 c in the lower desmoinesian to an average temperature of 32 3 c in the missourian this temperature change is coincident with a significant change in the composition of wetland vegetation in euramerica which has been attributed to a shift in low latitude pennsylvanian climate towards warmer and drier conditions in the late pennsylvanian this study reveals the presence of a dynamic late paleozoic paleoequatorial icehouse climate characterized by significant low latitude temperature variability unprecedented on modern earth

multiplatform observations of boundary layer structure in the outer rainbands of landfalling typhoons this paper analyzes data collected from a new set of observational platforms in the coastal area of china which consist of a mobile observation system meteorological tower automatic weather station and doppler radars to investigate the mean and turbulent boundary layer structure and evolution during the landfall of typhoons an example of these data is provided from typhoon morakot 2009 vertical profiles of wind velocities and thermodynamic parameters from the observed data allow us to identify different boundary layer structures during and after landfall these structures sampled in regions of the outer core are stratified into periods where convection is occurring termed convective and periods where convection has recently 2 h occurred termed postconvective data analyses show that the thermodynamic mixed layer depth and inflow layer depth are higher during the convective period than the postconvective period the mixed layer depth is found to be within the strong inflow layer but the height of the maximum tangential wind speed is above the inflow layer during both periods contrary to recent observational studies of the boundary layer structure of tropical cyclones over water high frequency wind data show that momentum flux turbulent kinetic energy tke and integral length scales of wind velocities are all much larger during the convective period than the postconvective period the results suggest that convective downdrafts may play an important role in modulating turbulent flux tke vertical mixing and boundary layer recovery processes

spectral characteristics of turbulence in the hurricane boundary layer over the ocean between the outer rain bands spectra and cospectra of wind velocity potential temperature and humidity have been analysed using data collected in the atmospheric boundary layer in hurricanes fabian 2003 and isabel 2003 during the coupled boundary layer air sea transfer cblast hurricane experiment the spectra and cospectra are normalized following the surface layer scaling methods according to similarity theory it is found that the cblast data gathered in the mixed layer between the outer rain bands below 400 m can be grouped into well defined curves for spectra of wind velocity potential temperature and humidity and for cospectra of momentum and humidity flux however the cospectra of sensible heat flux do not exhibit well defined universal shape the cblast universal shape spectra and cospectra generally resemble the shapes of those from previous studies but shift to higher frequencies that correspond to smaller wavelengths of turbulent eddies that contain most of the energy this work highlights the structural difference between the hurricane boundary layer and the standard atmospheric boundary layer over land and ocean copyright 2010 royal meteorological society

low level thermodynamic kinematic and reflectivity fields of hurricane guillermo 1997 during rapid intensification abstract from 0600 utc 2 august to 1200 utc 3 august hurricane guillermo 1997 deepened by 54 hpa over the eastern north pacific ocean easily exceeding the thresholds that define rapid intensification ri the noaa wp 3ds observed a portion of this ri with similar two aircraft missions on consecutive days the aircraft jettisoned 70 successful global positioning system gps dropwindsondes or gps sondes which reveal how conditions in the lower troposphere on the octant to quadrant scale evolved within 250 km of the eye reflectivity fields demonstrate that the deepening is correlated with a spiraling in of the northern eyewall that reduces the eye diameter by 10 km this behavior contrasts the more uniform contraction witnessed during eyewall replacement cycles mixing between the lower eye and eyewall as detailed by other investigators appears to have triggered the reduction in the eye diameter after ri the eyewall remains asymmetrical with the tallest echo tops and heaviest rain rates located o

comments on symmetric and asymmetric structures of hurricane boundary layer in coupled atmosphere wave ocean models and observations abstract in a recent paper lee and chen 2012 hereafter lc12 presented numerical simulations of symmetric and asymmetric hurricane boundary layer structures in a fully coupled atmosphere wave ocean model and used these simulations to compare aspects of the boundary layer structure against an analysis of observations one of their main conclusions was that the azimuthally averaged inflow layer tends to misrepresent the overall inflow structure in tropical cyclones especially the asymmetric structure p 3593 another main conclusion was that the complicated asymmetric three dimensional boundary layer structures attributed by them to be due in part to the air sea and wind wave coupling make it difficult to parameterize the atmosphere wave ocean coupling effects without a fully coupled model p 3593 after careful examination of their study we have a number of questions regarding their methodology their interpretations including their interpretations of previous literature and their conclusions specifically we inquire about aspects of the methodology for defining the dynamical boundary layer depth the selection of the boundary layer scheme and we question the conclusions inferred in addition to the foregoing concerns inaccuracies in their literature review are noted and inconsistencies between their conclusions and reported results are identified for many decades physical processes across the air sea interface and within the atmospheric boundary layer have been known to be essential for the development and maintenance of a tropical cyclone ooyama 1969 emanuel 1986 1995 smith et al 2009 smith and montgomery 2010 bryan and rotunno 2009 bryan 2012 however the boundary layer is the least observed part of a storm in particular its turbulence structure with the advent of the global positioning system gps dropsonde hock and franklin 1999 the mean boundary layer structure has been progressively studied

the lowermost mantle beneath northern asia i multi azimuth studies of a d heterogeneity summary in most areas of the globe it is only possible to sample the lowermost mantle or d region with a limited range of azimuths this is due to limitations in source receiver geometries an exception is the region beneath northern siberia where we are able to sample d along orthogonal great circle paths using northern pacific earthquakes recorded in europe and hindu kush earthquakes recorded in canada receiver vespagrams slant stacks of one source recorded at many receivers for a kurile event recorded at the german regional seismic network grsn and the grafenberg array and source vespagrams many sources one receiver of hindu kush events recorded at stations of the canadian national seismograph network cnsn show reflections from a discontinuity at the top of d vespagrams for real data are compared to vespagrams for synthetic data in order to guide their interpretation additional support for our interpretation comes from frequency wavenumber f k analysis which provides a measure of the slowness and azimuth of a given phase the traveltimes of the d reflected phases are then used to provide estimates of d thickness in regions where the roughly orthogonal paths overlap we estimate the thickness to be 310 15 km which is in agreement with existing models for this region we also estimate a thickness of 210 15 km in a previously unsampled region east of this area using the slowness backazimuth and traveltime values for a third source receiver combination we find a reflection point at a depth of 2800 km thickness of d of 91 km in a region several degrees to the west these results and those of previous studies suggest considerable topographic relief 100 km over distances of less than 5 approximately 300 km at the cmb comparing the results from this study with results from other seismic studies of d structure in this area we find this to be a complicated region which exhibits heterogeneity on many scales this region may be the lower mantle graveyard of the subducted izanagi plate and one interpretation of this complexity is that it is due to subduction related deformation at the base of the mantle

vertical motions in intense hurricanes abstract hurricane vertical motion properties are studied using aircraft measured 1 hz time series of vertical velocity obtained during radial penetrations of four mature hurricanes a total of 115 penetrations from nine flight sorties at altitudes from 0 5 to 6 1 km are included in the data set convective vertical motion events are classified as updrafts or downdrafts if the vertical velocity was continuously positive or negative for at least 500 m and exceed an absolute value of 0 5 m s 1 over 3000 updrafts and nearly 2000 downdrafts are included in the data set a second criteria was used to define stronger events called cores this criteria required that upward or downward vertical velocity be continuously greater than an absolute value of 1 m s 1 for at least 500 m the draft and core properties are summarized as distributions of average and maximum vertical velocity diameter and vertical mass transport in two regions eyewall and rainband in both regions updrafts dominated over downdraft

sharpness of the d discontinuity beneath the cocos plate implications for the perovskite to post perovskite phase transition 1 the depth extent or sharpness of the d seismic velocity discontinuity is determined by modeling distance dependence of reflected s wave signals sampling the lowermost mantle beneath the cocos plate the data spanning distances from 64 to 83 and grouped in two small turning point bins from 5 to 10 n and 10 to 15 n are compatible with a sharp 1 to 2 shear velocity increase near 300 km above the core mantle boundary but not with reflection from a transition zone extending more than 30 km in depth interpretation of the velocity structure as the result of magnesium silicate perovskite undergoing a phase transition to post perovskite requires limited presence of al and fe which will broaden the phase transition current experiments indicate that the phase transition may occur over 5 gpa 90 km in pyrolitic material requiring either distinct chemistry or dynamical mechanisms to sharpen the phase transition for this high velocity sub circum pacific region

seismic imaging the d region beneath the central atlantic abstract the lowermost mantle beneath the central atlantic is bounded by the western edge of african large low shear wave province llsvp and a high velocity region beneath the eastern americas which is attributed to the accumulated subducted slab material at the core mantle boundary cmb data recorded at broadband seismic arrays in western europe and morocco allow us to investigate the detailed structure beneath the central atlantic which provides an important constraint on how remnant slab material and llsvp interact and reshape the d layer here we exploit lower mantle triplicated s waveform data from deep earthquakes beneath south america our modelling results show that the d discontinuity is constantly observed from north to south beneath the central atlantic but at varied depths and with varied shear velocities in the lowermost mantle beneath east of caribbean our results indicate a sharp 2 1 shear velocity increase at 340 km above the cmb representing a possible bridgmanite dominant normal mantle d layer whereas the models of northern and southern portions of central atlantic indicate a gradual velocity increase of 4 2 across 200 km starting from 360 km above the cmb downwards we also find a distinct low velocity zone on top of the velocity jump which can be interpreted as an upwelling produced by the dynamic response of ancient slab material reaching the cmb

efficacy of the post perovskite phase as an explanation for lowermost mantle seismic properties constraining the chemical rheological and electromagnetic properties of the lowermost mantle d is important to understand the formation and dynamics of the earth s mantle and core to explain the origin of the variety of characteristics of this layer observed with seismology a number of theories have been proposed including core mantle interaction the presence of remnants of subducted material and that d is the site of a mineral phase transformation this final possibility has been rejuvenated by recent evidence for a phase change in mgsio3 perovskite thought to be the most prevalent phase in the lower mantle at near core mantle boundary temperature and pressure conditions here we explore the efficacy of this post perovskite phase to explain the seismic properties of the lowermost mantle through coupled ab initio and seismic modelling of perovskite and post perovskite polymorphs of mgsio3 performed at lowermost mantle temperatures and pressures we show that a post perovskite model can explain the topography and location of the d discontinuity apparent differences in compressional and shear wave models and the observation of a deeper weaker discontinuity furthermore our calculations show that the regional variations in lower mantle shear wave anisotropy are consistent with the proposed phase change in mgsio3 perovskite

p and s wave reflectors in d beneath southeast asia summary earthquakes from the south pacific region recorded at the kyrgyz seismic network knet and the ghengis network both part of the tien shan continental dynamics study have been analysed to search for evidence of reflections from the d region the reflection points of this source receiver combination are in a seismically fast area beneath southeast asia employing several array methods we find evidence for reflections from a d reflector in both p and s waves the reflector depth generally agrees for both wave types there is some evidence for a second deeper reflector in this region migrating the data suggests a lower seismic reflector beneath the northeastern end of the study region the waveforms of p and s waves imply that the upper reflector has a negative impedance contrast for p but a positive impedance contrast for s several possibilities are discussed for generating the observed reflector s with the post perovskite phase transition in combination with a cold slab being the preferred explanation

mesoscale and convective scale characteristics of mature hurricanes part ii inner core structure of hurricane allen 1980 abstract the eyewall structure of hurricane alien is examined from analyses of multiple aircraft data on two days 5 and 8 august 1980 these data sets are unique in that for the first time three instrumented aircraft executed coordinated radial penetrations of the eyewall at multiple levels the data collected on 5 august illustrate the persistence of various features on horizontal scales 10 km over several hours composite cross sections constructed from the 8 august data show similar structure although the eye diameter had decreased to less than half that of 5 august the convergence of air in the eyewall was highly two dimensional this convergence supported organized ascent that was along the inner edge of the high reflectivity region and displaced inward several kilometers from the radius of maximum wind rmw a mean eyewall updraft of 5 6 m s 1 is computed from integration of the two dimensional continuity equation embedded within the two dimensional eyewall were cores of high reflectivity t

seismic anisotropy beneath the continents probing the depths of geology seismic anisotropy beneath continents is analyzed from shear wave splitting recorded at more than 300 continental seismic stations anisotropy is found to be a ubiquitous property that is due to mantle deformation from past and present orogenic activity the observed coherence with crustal deformation implies that the mantle plays a major if not dominant role in orogenies no evidence is found for a continental asthenospheric decoupling zone suggesting that continents are coupled to general mantle circulation

partial melting in a thermo chemical boundary layer at the base of the mantle abstract seismological detections of complex structures in the lowermost mantle boundary layer the d region motivate a conceptual model of a compositionally stratified thermo chemical boundary layer tcbl within which lateral temperature variations sustained by large scale mid mantle flow cause variations of partial melt fraction partial melt fractions of from 0 to 30 in the tcbl occur due to the eutectic of the boundary layer material lying below the high temperature at the core mantle boundary cmb coupled with the presence of steep thermal gradients across the boundary layer regions of the tcbl with the highest temperatures have extensive partial melting producing lateral chemical variations and strong effects on seismic velocities and boundary layer dynamics this tcbl concept provides a relatively simple framework that can plausibly account for diverse seismological observations such as predominance of large scale volumetric elastic wave velocity heterogeneity in the boundary layer laterally extensive but intermittent abrupt shear and compressional velocity increases and decreases at the top of the d region small scale topography of d velocity discontinuities thin ultra low velocity zones at the cmb widespread shear wave anisotropy in d bulk sound velocity anomalies detected in low shear velocity regions of d and large scale upwellings from the most extensively melted regions of the boundary layer neutral or negative buoyancy of the partial melt in the tcbl is required along with an increase in bulk modulus and some density increase of the boundary layer material relative to the overlying mantle more complex models in which the partially melted chemical boundary layer is laterally displaced by mid mantle downwellings are also viable but these appear to require additional special circumstances such as a phase change efficient segregation of slab crustal material or abrupt onset of anisotropy in order to account for rapid velocity increases at the top of d the precise nature of the compositional anomaly or anomalies in d and the eutectic composition of this zone are yet to be determined but it appears likely that partial melting within the lowermost mantle plays a paramount role in the observed seismic velocity heterogeneity increased resolution geodynamic calculations of dense boundary layer structures with partial melting and attendant viscosity reductions and chemical heterogeneity are needed to quantify this tcbl concept

an sh hybrid method and shear velocity structures in the lowermost mantle beneath the central pacific and south atlantic oceans 1 an sh hybrid method is developed for calculating synthetic seismograms involving two dimensional localized heterogeneous structures the hybrid method is a combination of analytic and numerical methods with the numerical method finite difference applied in the heterogeneous region only and analytical methods applied outside the region generalized ray theory solutions from a seismic source are used to initiate the finite difference calculation and seismic responses at the earth s surface are obtained from the finite difference output by applying the kirchhoff theory we apply the hybrid method and study sh wave propagation near the bottom of the mantle the shear velocity structures and the interaction of sh waves with these velocity structures at the base of the mantle beneath the central pacific and south atlantic oceans are of particular importance the observed sh waves sampling these two regions of the core mantle boundary show very different characteristics across the epicentral distance range of 83 108 the sh waves sampling the core mantle boundary beneath the central pacific show a linearly increasing delay of 4 s from 98 to 108 and discernible scs phases up to an epicentral distance of 102 the sh waves propagating through the base of the mantle beneath the south atlantic ocean on the other hand exhibit a linearly increasing delay of 10 s from 98 to 108 discernible multiple scs phases with a same slowness as the direct sh waves up to 108 and rapid variations of waveforms across small epicentral distances synthetic tests indicate that while the observations sampling the central pacific can be explained by a negative shear velocity gradient of 3 relative to the preliminary reference earth model at the bottom 300 km of the mantle those sampling the south atlantic ocean require a 300 km thick bottom boundary layer with a larger negative velocity gradient up to 10 and steeply dipping edges the negative velocity gradient at the base of mantle beneath the south atlantic ocean can be best explained by partial melt driven by a compositional change produced in the early earth s history and a vertical thermal gradient within the layer while that beneath the central pacific may reasonably be attributed to pure thermal effects within a thermal boundary layer

an observational case for the prevalence of roll vortices in the hurricane boundary layer abstract doppler velocity data from weather surveillance radar 1988 doppler wsr 88d radars during four hurricane landfalls are analyzed to investigate the presence of organized vortices in the hurricane boundary layer hbl the wavelength depth magnitude and track of velocity anomalies were compiled through analysis of doppler velocity data the analysis reveals alternating bands of enhanced and reduced azimuthal winds closely aligned with the mean wind direction resulting statistics provide compelling evidence for the presence of organized secondary circulations or boundary layer rolls across significant areas during four hurricane landfalls the results confirm previous observations of the presence of rolls in the hbl a potential limitation of the study presented here is the resolution of the wsr 88d data in particular analysis of higher resolution data e g from the doppler on wheels is needed to confirm that data aliasing has not unduly impacted the statistics reported here momentum flux

warm core formation in tropical storm humberto 2001 at 0600 utc 22 september 2001 humberto was a tropical depression with a minimum central pressure of 1010 hpa twelve hours later when the first global positioning system dropwindsondes gps sondes were jettisoned humberto s minimum central pressure was 1000 hpa and it had attained tropical storm strength thirty gps sondes radar from the wp 3d and in situ aircraft measurements are utilized to observe thermodynamic structures in humberto and their relationship to stratiform and convective elements during the early stage of the formation of an eye the analysis of tropical storm humberto offers a new view of the pre wind induced surface heat exchange pre wishe stageoftropicalcycloneevolution humbertocontainedamesoscaleconvectivevortex mcv similar to observations of other developing tropical systems the mcv advects the exhaust from deep convection in the form of an anvil cyclonically over the low level circulation center on the trailing edge of the anvilanareaofmesoscaledescentinducesdryadiabaticwarmingin thelowertroposphere thenascentwarm core at low levels causes the initial drop in pressure at the surface and acts to cap the boundary layer bl as bl air flows into the nascent eye the energy content increases until the energy is released from under the cap on the down shear side of the warm core in the form of vigorous cumulonimbi which become the nascent eyewall this series of events show one possible path in which a mesoscale convective system may evolve into a warm cored structure and intensify into a hurricane

seismic velocity structures and detailed features of the d discontinuity near the core mantle boundary beneath eastern eurasia abstract shear and compressional velocity structures and features of the d discontinuity near the core mantle boundary cmb beneath eastern eurasia are studied based on forward waveform modeling and differential travel time analysis of scsh sh sscs ss pcp p and ppcp pp phases high quality differential travel time analysis reveals two high velocity patches spanning a width of 3000 km and separated by a 300 km wide normal velocity gap the maximum shear and compressional velocity perturbations reach 3 8 and 2 7 respectively seismic data indicate that the d discontinuity emerges in the high velocity patches and disappears in the normal velocity gap furthermore the features of the d discontinuity although constrained by rather sparse seismic data vary from diffusive discontinuities in the eastern patch to sharp discontinuities in the western patch the d discontinuities occur at about 270 km above the cmb in the eastern patch with a shear velocity jump of 3 0 5 0 and a transitional depth of at least 100 km and at 250 km above the cmb in the western patch with an abrupt shear velocity jump of 5 0 a diffusive p wave discontinuity is also observed in the eastern patch with the similar features of the s wave discontinuity the inferred features of the d discontinuity can be explained by the post perovskite transformation in the lower mantle the observations that the d discontinuities occur only in the high velocity patches may be due to the effect of the positive clapeyron slope of the post perovskite transition and the varying transitional depths of the d discontinuity in the high velocity regions may be caused by the compositional effects on the post perovskite transition in the presence of strong variations of composition within the high velocity anomalies the high velocity patches geographically correlate with the subduction of the pacific and indian plates in the past 30 60 ma and the normal velocity gap falls into the subduction gap between the pacific and indian plates these geographical correlations raise the possibility that the existence of the d discontinuity is intimately related to the presence of the past subduction material at the cmb and varying features of the discontinuity further suggest existence of strong variations of composition within the subduction materials at the cmb

evolution of the inflow boundary layer of hurricane gilbert 1988 abstract on 12 september 1988 the two noaa wp 3d aircraft conducted an experiment in and around an intense outer rainband located 175 km southeast of the center of hurricane gilbert radial height cross sections along a constant azimuth reveal a rapid and an exceptionally large increase of the equivalent potential temperature e of the inflow but in a region radially outward from the rainband kinematic analyses that incorporate both in situ and pseudo dual doppler data illustrate that the inflow is only 2 km deep and strongly divergent prior to reaching the convective core of the band the doppler derived wind fields which compare favorably with the in situ wind fields demonstrate that there is a radially outward or return flow directly above the inflow soundings show that this return flow is unusually moist despite being dominated by mesoscale descent which contrasts the dry conditions found under the anvil of virtually all tropical mesoscale convective systems a one dimensional general structure

the tilt of the leading edge of mesoscale tropical convective lines abstract the tilt with height of the leading edge of seven mesoscale convective lines in gate is determined by two independent methods when averaged over time and along the line axis the tilt is found to he surprisingly shallow between 20 and 35 degrees from the horizontal this is distinct from the slopes of the individual towers which can be much steeper the line leading edge slope corresponds to the ratio of the vertical to horizontal velocity relative to the line motion of representative embedded convective cores