subrainband structure and dynamic characteristics in the principal rainband of typhoon hagupit 2008 abstractthe principal rainband in tropical cyclones is currently depicted as a solitary and continuous precipitation region however the airborne radar observations of the principal rainband in typhoon hagupit 2008 reveal multiple subrainband structures these subbands possess many characteristics of the squall lines with trailing stratiform in the midlatitudes and are different from those documented in previous principal rainband studies the updraft and reflectivity cores are upright and elevated the updraft is fed by a low level radial outflow from the inner side the tangential wind speed shows a clear midlevel jet on the inner side of the reflectivity core except for the structural similarities the dynamics of the subbands is also similar to the squall lines the local environment near the subbands shows little convective inhibition modest instability and vertical wind shear the temperature retrieval shows a cold pool structure in the stratiform precipitation region the estimated vertical w

vertical velocity characteristics of deep convection over darwin australia abstract continuous vertical velocity measurements using a 50 mhz wind profiler located at darwin in northern australia during periods of active convection have been analyzed this dataset is dominated by continental type convection numerous examples of shallow deep and decaying convection were seen and it is shown that only the deep systems have substantial tilts to the draft structure the most intense updrafts occur above the freezing level but shallow convection also produces large amplitude vertical motions the strength of these updrafts in this dataset is very similar to other tropical oceanic data that observation is consistent with the idea that the magnitude of the updrafts is much less in the tropics than for intense midlatitude convection because the convective available potential energy is distributed over a much deeper layer in the tropics although more intense updrafts may be present at other tropical locations such as the tiwi islands north of darwin the size of the cores however

a multiscale numerical study of hurricane andrew 1992 part iv unbalanced flows abstract despite considerable progress in understanding the hurricane vortex using balanced models the validity of gradient wind balance in the eyewall remains controversial in observational studies in this paper the structure and development of unbalanced forces and flows in hurricanes are examined through the analyses of the radial momentum and absolute angular momentum aam budgets using a high resolution i e x 6 km fully explicit simulation of hurricane andrew 1992 it is found from the radial momentum budgets that supergradient flows and accelerations even after temporal and azimuthal averaging are well organized from the bottom of the eye center to the upper outflow layer in the eyewall the agradient accelerations are on average twice greater than the local coriolis force and caused mainly by the excess of the centrifugal force over the pressure gradient force it is shown by the aam budgets that supergradient flows could occur not only in the inflow region as a result of the inw

the role of storm relative advection of absolute angular momentum in strengthening of atlantic tropical cyclones 1 this study examined absolute angular momentum tendency in atlantic tropical cyclones each advective and torque term in the storm relative eulerian absolute angular momentum tendency equation was calculated in a storm relative reference frame using modeled and observational data 18 storms between 2004 and 2006 were simulated using the hurricane weather research and forecast model in addition the storm relative advection of absolute angular momentum was calculated using reconnaissance aircraft wind data from 12 atlantic hurricanes which occurred between 2003 and 2007 through methods of statistical correlation categorical composition and linear regression it was found that mid level horizontal advection of relative angular momentum was most relevant to 12 hour strength change in the modeled tropical cyclones mid level horizontal advection of relative angular momentum was most relevant to intensity change in the observed hurricanes while mid level advection of earth s angular momentum was found to be most closely related to strength change in observed hurricanes

the structure and decay of a rainband in hurricane irene 1981 abstract the mesoscale thermodynamic kinematic and reflectivity structure of a rainband observed in hurricane irene on 27 september 1981 is presented data are from 16 aircraft passes from 150 to 4700 m msl through the rainband which was located ssw of the circulation center of the northward moving hurricane cross sections of the rainband as a function of height and radial distance from the storm center reveal the following 1 little or no decrease of e in the subcloud layer associated with the weak convective cells in the rainband 2 large differences in static stability between the north and south sides of the band 3 a change of the radial wind component in the subcloud layer from flow toward the circulation center to flow away from it as the rainband weakens the decay of the rainband is believed to be related to mesoscale subsidence and the location of the rainband relative to the motion of the hurricane melting and evaporation of hydrometeors falling between the eyewall and the rainband are

a theory for strong long lived squall lines abstract we study herein the mechanics of long lived line oriented precipitating cumulus convection squall lines using two and three dimensional numerical models of moist convection these models used in juxtaposition enable us to address the important theoretical issue of whether a squall line is a system of special long lived cells or whether it is a long lived system of ordinary short lived cells our review of the observational literature indicates that the latter is the most consistent paradigm for the vast majority of cases but on occasion a squall line may be composed of essentially steady supercell thunderstorms the numerical experiments presented herein show that either type of squall line may develop from an initial line like disturbance depending on the magnitude and orientation of the environmental shear with respect to the line with shallow shear oriented perpendicular to the line a long lived line evolves containing individually short lived cells our analysis of this type o

a convective cell in a hurricane rainband abstract on 10 october 1983 the two noaa wp 3d aircraft completed a mission designed to provide airborne doppler radar data for a convective cell embedded in a weak rainband on the trailing side of hurricane raymond comparisons of the wind field produced from the pseudo dual doppler radar technique with in situ wind measurements suggest that the larger convective scale feature may be resolved if the sampling time is kept to a minimum the convective cell was found to move downband faster than any environmental winds but slightly slower than the winds found in the reflectivity core that delineates the cell in the core of the cell the tangential wind is increased and the radial inflow turns to outflow with respect to the circulation center the flow field demonstrates that the downband stratiform portion of a rainband is not from cells currently active since the updraft detrains upwind relative to the cell but rather it is due to the fallout from ice particles placed into the upper troposphere by clouds t

dynamics of the stratiform sector of a tropical cyclone rainband abstractairborne doppler radar documented the stratiform sector of a rainband within the stationary rainband complex of hurricane rita the stratiform rainband sector is a mesoscale feature consisting of nearly uniform precipitation and weak vertical velocities from collapsing convective cells upward transport and associated latent heating occur within the stratiform cloud layer in the form of rising radial outflow beneath downward transport is organized into descending radial inflow in response to two regions of latent cooling in the outer upper regions of the rainband sublimational cooling introduces horizontal buoyancy gradients which produce horizontal vorticity and descending inflow similar to that of the trailing stratiform region of a mesoscale convective system within the zone of heavier stratiform precipitation melting cooling along the outer rainband edge creates a midlevel horizontal buoyancy gradient across the rainband that drives air farther inward beneath the brightband the organi

convective scale downdrafts in the principal rainband of hurricane katrina 2005 abstract airborne doppler radar data collected during the hurricane rainband and intensity change experiment rainex document downdrafts in the principal rainband of hurricane katrina 2005 inner edge downdrafts ieds originating at 6 8 km altitude created a sharp reflectivity gradient along the inner boundary of the rainband low level downdrafts llds evidently driven by precipitation drag originated at 2 4 km within the heavy rain cells of each convective element the ied and lld were spatially separated by but closely associated with the updrafts within the rainband the ied was forced aloft by pressure perturbations formed in response to the adjacent buoyant updrafts once descending the air attained negative buoyancy via evaporative cooling from the rainband precipitation a convective scale tangential wind maximum tended to occur in the radial inflow at lower levels in association with the ied which enhanced the inward flux of angular momentum at lower levels convergence at the base of the

mechanisms for the generation of mesoscale vorticity features in tropical cyclone rainbands a high resolution tropical cyclone model with explicit cloud microphysics has been used to investigate the dynamics and energetics of tropical cyclone rainbands analysis of the vorticity interactions that occur within the simulated rainbands demonstrates that couplets of cyclonic anticyclonic mesovortices can be produced in outer bands the primary source of this vorticity is the upward tilting of system generated horizontal vorticity by diabatic heating gradients the vertical heating gradient in the stratiform cloud also creates a potential vorticity pv dipole that accelerates the tangential flow and develops a midlevel jet the strength of the jet is enhanced by the vortex pair that is oriented radially across the rainband the fourier decomposition of the absolute vorticity field shows two counterpropagating vortex rossby waves associated with the rainband the wave located on the inner side of the band transports energy toward the vortex center the outer wave is made up of high wavenumbers and uses the vorticity gradients generated by the rainband the results support the hypothesis that the heating profile in the stratiform regions of rainbands generates cyclonic pv across the freezing level which develops a midlevel jet this mechanism creates a vorticity gradient that enables the propagation of vortex rossby waves that could allow the rainbands to interact with the mean flow and potentially influence the evolution of the storm by contributing to the symmetric component of vorticity and the development of secondary eyewalls

external influences on hurricane intensity part iii potential vorticity structure abstract the interaction of hurricane elena 1985 with a baroclinic wave was reexamined using both potential vorticity pv and a formulation for eliassen palm fluxes in cylindrical coordinates the hurricane began to deepen rapidly as a narrow upper level positive pv anomaly became nearly superposed over the low level center the intensification appeared to represent an evaporation wind feedback activated by constructive interference of the pv anomalies enhanced convection associated with this process eroded the upper pv anomaly and prevented it from crossing the hurricane and reversing the intensification the eliassen palm flux divergence showed that maximum eddy activity remained in the upper troposphere prior to the reintensification this activity was produced in part because the action of the outflow anticyclone of the hurricane contributed to synoptic scale wave breaking the upper level pv anomaly that approached the center was much narrower in extent than the original synoptic scale trough th

sheared deep vortical convection in pre depression hagupit during tcs08 1 airborne doppler radar observations from the recent tropical cyclone structure 2008 field campaign in the western north pacific reveal the presence of deep buoyant and vortical convective features within a vertically sheared westward moving pre depression disturbance that later developed into typhoon hagupit on two consecutive days the observations document tilted vertically coherent precipitation vorticity and updraft structures in response to the complex shearing flows impinging on and occurring within the disturbance near 18 north latitude the observations and analyses herein suggest that the low level circulation of the pre depression disturbance was enhanced by the coupling of the low level vorticity and convergence in these deep convective structures on the meso gamma scale consistent with recent idealized studies using cloud representing numerical weather prediction models further examination of these new observations is needed to quantify the relative role of these vortical convection features in the tropical cyclone spin up process

organizational modes of midlatitude mesoscale convective systems this paper discusses common modes of mesoscale convective organization using 2 km national composite reflectivity data the authors investigated linear mesoscale convective systems mcss that occurred in the central united states during may 1996 and may 1997 based upon the radar observed characteristics of 88 linear mcss the authors propose a new taxonomy comprising convective lines with trailing ts leading ls and parallel ps stratiform precipitation while the ts archetype was found to be the dominant mode of linear mcs organization the ls and ps archetypes composed nearly 40 of the studied population in this paper the authors document the characteristics of each linear mcs class and use operational surface and upper air data to describe their different environments in particular wind profiler data reveal that the stratiform precipitation arrangement associated with each class was roughly consistent with the advection of hydrometeors implied by the mean middle and upper tropospheric storm relative winds which were significantly different among the three mcs modes case study examples are presented for both the ls and ps classes which have received relatively little attention to this point as well the authors give a general overview of the synoptic scale meteorology accompanying linear mcss in this study which was generally similar to that observed by previous investigators

nanodiamond rich layer across three continents consistent with major cosmic impact at 12 800 cal bp abstracta major cosmic impact event has been proposed at the onset of the younger dryas yd cooling episode at 12 800 150 years before present forming the yd boundary ydb layer distributed over 50 million km2 on four continents in 24 dated stratigraphic sections in 10 countries of the northern hemisphere the ydb layer contains a clearly defined abundance peak in nanodiamonds nds a major cosmic impact proxy observed nd polytypes include cubic diamonds lonsdaleite like crystals and diamond like carbon nanoparticles called n diamond and i carbon the nd abundances in bulk ydb sediments ranged up to 500 ppb mean 200 ppb and that in carbon spherules up to 3700 ppb mean 750 ppb 138 of 205 sediment samples 67 contained no detectable nds isotopic evidence indicates that ydb nds were produced from terrestrial carbon as with other impact diamonds and were not derived from the impactor itself the ydb layer is also marked by abundance peaks in other impact related proxies including

angular momentum transports in tropical cyclones angular momentum budget equations are developed for eulerian and lagrangian cylindrical coordinate systems centred on a tropical cyclone all non friction terms are reduced to boundary transports and the effects of cyclone motion in the eulerian coordinate system are isolated a number of intensifying and weakening composite northwest pacific cyclones are used to illustrate the physical role and relative importance of each process in the maintenance or destruction of tropical cyclones at various intensity stages

origin and provenance of spherules and magnetic grains at the younger dryas boundary abstract one or more bolide impacts are hypothesized to have triggered the younger dryas cooling at 12 9 ka in support of this hypothesis varying peak abundances of magnetic grains with iridium and magnetic microspherules have been reported at the younger dryas boundary ydb we show that bulk sediment and or magnetic grains microspherules collected from the ydb sites in arizona michigan new mexico new jersey and ohio have 187os 188os ratios 1 0 similar to average upper continental crust 1 3 indicating a terrestrial origin of osmium os in these samples in contrast bulk sediments from ydb sites in belgium and pennsylvania exhibit 187os 188os ratios 1 0 and at face value suggest mixing with extraterrestrial os with 187os 188os of 0 13 however the os concentration in bulk sample and magnetic grains from belgium is 2 8 pg g and 15 pg g respectively much lower than that in average upper continental crust 31 pg g indicating no meteoritic contribution the ydb site in pennsylvania is remarkable in yielding 2 to 5 mm diameter spherules containing minerals such as suessite fe ni silicide that form at temperatures in excess of 2000 c gross texture mineralogy and age of the spherules appear consistent with their formation as ejecta from an impact 12 9 ka ago the 187os 188os ratios of the spherules and their leachates are often low but os in these objects is likely terrestrially derived the rare earth element patterns and sr and nd isotopes of the spherules indicate that their source lies in 1 5 ga quebecia terrain in the grenville province of northeastern north america

quantifying the distribution of nanodiamonds in pre younger dryas to recent age deposits along bull creek oklahoma panhandle usa high levels of nanodiamonds nds have been used to support the transformative hypothesis that an extraterrestrial et event comet explosion triggered younger dryas changes in temperature flora and fauna assemblages and human adaptations firestone rb et al 2007 proc natl acad sci usa 104 41 16016 16021 we evaluate this hypothesis by establishing the distribution of nds within the bull creek drainage of the beaver river basin in the oklahoma panhandle the earlier report of an abundance spike of nds in the bull creek i younger dryas boundary soil is confirmed although no pure cubic diamonds were identified the lack of hexagonal nds suggests bull creek i is not near any impact site potential hexagonal nds at bull creek were found to be more consistent with graphene graphane an additional nd spike is found in deposits of late holocene through the modern age indicating nds are not unique to the younger dryas boundary nd distributions do not correlate with depositional environment pedogenesis climate perturbations periods of surface stability or cultural activity

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 wide rainband in a developing tropical cyclone abstract on 18 january 1987 the three aircraft from the equatorial mesoscale experiment emex completed a mission designed to identify the mesoscale reflectivity kinematic and thermodynamic structure of a convectively active rainband on the leading edge of developing tropical cyclone irma the reflectivity structure determined from land based and aircraft radars reveals that the band consisted of an unusually wide 80 km region of convective clouds that did not maintain a linear organization high e air entered from both sides in the subcloud and lower cloud layer thermodynamically the rainband was benign in the sense that it did not produce cold downdrafts or large regions of low e air that would limit the energy of the low level inflow to the developing eyewall region kinematically the band was a preferred location for the enhancement of the wind component parallel to the band the low level flow was along rather than across the major axis of the band above 4 5 km flow was from the inner to

tracking a long lasting outer tropical cyclone rainband origin and convective transformation abstractthis study used radar and surface observations to track a long lasting outer tropical cyclone rainband tcr of typhoon jangmi 2008 over a considerable period of time 10 h from its for

the dynamics of boundary layer jets within the tropical cyclone core part i linear theory abstract observations of wind profiles within the tropical cyclone boundary layer have until recently been quite rare the recent massive increase in observations due to the operational implementation of the global positioning system dropwindsonde has emphasised that a low level wind speed maximum is a common feature of the tropical cyclone boundary layer here is proposed a mechanism for producing such a maximum whereby strong inward advection of angular momentum generates the supergradient flow the processes that maintain the necessary inflow against the outward acceleration resulting from gradient wind imbalance are identified as being i vertical diffusion ii vertical advection and iii horizontal advection two complementary tools are used to diagnose the properties and dynamics of the jet the first presented here is a linear analytical model of the boundary layer flow in a translating tropical cyclone it is an extension of the classical ekman boundary layer model as well as of earlier w

convectively generated potential vorticity in rainbands and formation of the secondary eyewall in hurricane rita of 2005 abstracteyewall replacements in mature tropical cyclones usually cause intensity fluctuations one reason for eyewall replacements remaining a forecasting challenge is the lack of understanding of how secondary eyewalls form this study uses high resolution full physics model forecast fields of hurricanes katrina and rita 2005 to better understand potential vorticity pv generation in the rainbands and the role that convectively generated pv played in the formation of a secondary eyewall in hurricane rita previous studies have focused on dynamic processes in the inner core and or the effects of certain specified pv distributions however the initial development of a concentric pv ring in the rainband region has not been fully addressed katrina and rita were extensively observed by three research aircraft during the hurricane rainband and intensity change experiment rainex which was designed to study the interaction of the rainbands and the inner core rita developed a secondary eyewall and went

mesoscale and convective structure of a hurricane rainband abstract the mesoscale thermodynamic kinematic and radar structure of a hurricane floyd rainband observed on 7 september 1981 is presented data are from 26 aircraft passes through the rainband from 150 to 6400 m a composite technique which presents rainband structure as a function of distance from the storm circulation center reveals inflow from the outer edge of the band and a partial barrier to this flow below 3 km in the direction parallel to rainband orientation radar reveals cellular reflectivity structure on the upwind and central portions of the rainband the frequency of cellular precipitation decreases in favor of stratiform precipitation further downwind as the band spirals gradually towards the eyewall in the radial direction a decrease of 12 k in e is observed across the rainband in the subcloud layer convective scale up and downdrafts that are associated with cellular reflectivity structure are hypothesized to be responsible for the thermodynamic modification of the cloud and subc

kinematic structure of convective scale elements in the rainbands of hurricanes katrina and rita 2005 1 airborne doppler radar data collected during the hurricane rainband and intensity change experiment rainex show the convective scale air motions embedded in the principal rainbands of hurricanes katrina and rita these embedded convective cells have overturning updrafts and low level downdrafts originating at 2 4 km that enter the rainband on its radially outward side and cross over each other within the rainband as well as a strong downdraft emanating from upper levels 6 km on the radially inward side these vertical motion structures repeat from one convective cell to another along each rainband the resulting net vertical mass transport is upward in the upwind portion of the band and greatest in the middle sector of the principal rainband where the updraft motions contribute generally to an increase of potential vorticity below the 3 4 km level because the convective cells in the middle sector are systematically located radially just inside the secondary horizontal wind maximum shwm the local increase in vorticity implied by the convective mass transport is manifest locally as an increase in the strength of the shwm at midlevels 4 km the overturning updrafts of the convective cells tilt stretch and vertically transport vorticity such that the convergence of the vertical flux of vorticity strengthens the vorticity anomaly associated with the shwm this process could strengthen the shwm by several meters per second per hour and may explain how high wave number convective scale features can influence a low wave number feature such as the principal rainband and subsequently influence the primary vortex

external influences on hurricane intensity part i outflow layer eddy angular momentum fluxes abstract outflow layer winds were objectively analyzed every 12 h for 6 days during the life cycle of hurricane elena 1985 a high correlation was found between angular momentum fluxes by azimuthal eddies at large radii and central pressure changes in the storm 27 33 h later momentum flux by eddies exceeded that by the azimuthal mean outside the 800 km radius while vortex spinup by the eddies reached instantaneous magnitudes as large as 25 m s 1 day outflow maxima and minima repeatedly appeared more than 1000 km from the hurricane center and tracked inward with time the results provide evidence of significant environmental control on the behavior of the storm after reaching hurricane strength elena experienced a major secondary intensification associated with a large inward cyclonic eddy momentum flux produced by the passage of a middle latitude trough north of the hurricane an outflow maximum appeared radially inside of the eddy momentum source consistent with balanced vortex theory and tracke

clouds in tropical cyclones abstract clouds within the inner regions of tropical cyclones are unlike those anywhere else in the atmosphere convective clouds contributing to cyclogenesis have rotational and deep intense updrafts but tend to have relatively weak downdrafts within the eyes of mature tropical cyclones stratus clouds top a boundary layer capped by subsidence an outward sloping eyewall cloud is controlled by adjustment of the vortex toward gradient wind balance which is maintained by a slantwise current transporting boundary layer air upward in a nearly conditionally symmetric neutral state this balance is intermittently upset by buoyancy arising from high moist static energy air entering the base of the eyewall because of the radial influx of low level air from the far environment supergradient wind in the eyewall zone and or small scale intense subvortices the latter contain strong erect updrafts graupel particles and large raindrops produced in the eyewall fall out relatively quickly while ice splinters left

a squall line like principal rainband in typhoon hagupit 2008 observed by airborne doppler radar this study examines the structure and dynamics of typhoon hagupit s 2008 principal rainband using airborne radar and dropsonde observations the convection in hagupit s principal rainband was organized into a well defined line with trailing stratiform precipitation on the inner side individual convective cells had intense updrafts and downdrafts and were aligned in a wavelike pattern along the line the line averaged vertical cross section possessed a slightly inward tilting convective core and two branches of low level inflow feeding the convection the result of a thermodynamic retrieval showed a pronounced cold pool behind the convective line the horizontal and vertical structures of this principal rainband show characteristics that are different than the existing conceptual model and are more similar to squall lines and outer rainbands the unique convective structure of hagupit s principal rainband was associated with veering low level vertical wind shear and large convective instability in the environment a quantitative assessment of the cold pool strength showed that it was quasi balanced with that of the low level vertical wind shear the balanced state and the structural characteristics of convection in hagupit s principal rainband were dynamically consistentwith the theory ofcold pooldynamicswidely appliedtostrong andlong livedsquall lines theanalyses suggest that cold pool dynamics played a role in determining the principal rainband structure in addition to storm scale vortex dynamics

suspect cubic diamond impact proxy and a suspect lonsdaleite identification the presence of nanometer sized diamonds in purported younger dryas yd boundary dated sediments carbon spherules and greenland ice was cited as evidence of a yd impact event 1 although cubic and hexagonal lonsdaleite diamond have been found in shocked metamorphosed meteorites and are associated with terrestrial impact structures cubic diamonds are well known to occur in terrestrial deposits that have no associations with impact processes for example submicron and smaller cubic diamond crystals have been found recently in carbonaceous spherules isolated in upper soils from various german and belgian sites 2 lacking links to impact structures these diamonds are evidently not products of impact

the 12 13 january 1988 narrow cold frontal rainband observed during mfdp fronts 87 part i kinematics and thermodynamics abstract the kinematic and thermodynamic structure of a narrow cold frontal rainband ncfr observed during the english french german mfdp fronts 87 experiment is presented radiosonde data indicated a very weak convective instability below 1500 m altitude and a low level jet of 30 m s 1 from ssw before the arrival of the front a cooling of about 1 c associated with an airflow of 13 m s 1 from wsw after its passage a composite of wind and reflectivity fields from 17 dual doppler radar analyses shows high reflectivity values large convergence and relatively intense vertical motions associated with this ncfr at the 1000 m altitude a mean vertical cross section perpendicular to the surface front derived from three successive high resolution dual doppler scans is used to examine the general characteristics of the air circulation a structure apparently similar to that of a density current is observed above the 2 km altitude however air flowing at a speed faster than the surface front appreciably mod

comprehensive analysis of nanodiamond evidence relating to the younger dryas impact hypothesis during the end of the last glacial period in the northern hemisphere near 12 9k cal a bp deglacial warming of the bolling allerod interstadial ceased abruptly and the climate returned to glacial conditions for an interval of about 1300 years known as the younger dryas stadial the younger dryas impact hypothesis proposes that the onset of the younger dryas climate reversal pleistocene megafaunal extinctions and disappearance of the clovis paleoindian lithic technology were coeval and caused by continent wide catastrophic effects of impact bolide events in north america while there are no known impact structures dated to the younger dryas onset physical evidence of the impact bolide events is argued to be present in sediments spanning several continents at stratigraphic levels inferred to date to the bolling allerod younger dryas boundary ydb reports of nanometer to submicron sized diamonds in ydb sediments in particular the rare 2h hexagonal polytype of diamond lonsdaleite have been presented as strong evidence for shock processing of crustal materials we review the available data on diamonds in sediments and provide new data we find no evidence for lonsdaleite in ydb sediments and find no evidence of a spike in nanodiamond concentration at the ydb layer to support the impact hypothesis

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

tutorial on sound propagation outdoors concerns about noise in the community date back to the dawn of recorded history then after centuries of relatively little activity scientific interest grew during the 17th century and social concerns were again voiced during the 19th century many of the wave propagation mechanisms relevant outdoors were understood at least qualitatively by the late 1800s today knowledge of sound propagation phenomena is of great economic and social importance because of environmental and other concerns reality is more complicated than geometrical spreading above flat ground some grounds are acoustically hard like concrete and others soft as snow corresponding reflection coefficients are complex and vary with angle grounds may not be flat leading to shadow zones or alternatively multiple reflections at the ground gradients of wind or temperature refract waves either upwards upwind or in a temperature lapse or downwards downwind or in a temperature inversion atmospheric turbulence causes fluctuations in the acoustical effects many of these features mutually interact measured sound pressure levels owe as much to near surface weather and to ground shape and impedance as to acoustical factors such as source and receiver heights and their separation this tutorial paper emphasizes field measurements and simple physical interpretations

hurricane spiral bands abstract the spiral bands that occur in tropical cyclones can be conveniently divided into two classes outer bands and inner bands evidence is presented here that the outer bands form as the result of nonlinear effects during the breakdown of the intertropical convergence zone itcz through barotropic instability in this process a zonal strip of high potential vorticity the itcz shear zone or monsoon trough begins to distort in a varicose fashion with the potential vorticity pv becoming pooled in local regions that are connected by filaments of high pv as the pooled regions become more axisymmetric the filaments become thinner and begin to wrap around the pv centers it is argued that inner bands form in a different manner as a tropical cyclone intensifies due to latent heat release the pv field becomes nearly circular with the highest values of pv in the cyclone center the radial gradient of pv provides a state on which pv waves the generalization of rossby waves can propagate the nonline

evidence from central mexico supporting the younger dryas extraterrestrial impact hypothesis we report the discovery in lake cuitzeo in central mexico of a black carbon rich lacustrine layer containing nanodiamonds microspherules and other unusual materials that date to the early younger dryas and are interpreted to result from an extraterrestrial impact these proxies were found in a 27 m long core as part of an interdisciplinary effort to extract a paleoclimate record back through the previous interglacial our attention focused early on an anomalous 10 cm thick carbon rich layer at a depth of 2 8 m that dates to 12 9 ka and coincides with a suite of anomalous coeval environmental and biotic changes independently recognized in other regional lake sequences collectively these changes have produced the most distinctive boundary layer in the late quaternary record this layer contains a diverse abundant assemblage of impact related markers including nanodiamonds carbon spherules and magnetic spherules with rapid melting quenching textures all reaching synchronous peaks immediately beneath a layer containing the largest peak of charcoal in the core analyses by multiple methods demonstrate the presence of three allotropes of nanodiamond n diamond i carbon and hexagonal nanodiamond lonsdaleite in order of estimated relative abundance this nanodiamond rich layer is consistent with the younger dryas boundary layer found at numerous sites across north america greenland and western europe we have examined multiple hypotheses to account for these observations and find the evidence cannot be explained by any known terrestrial mechanism it is however consistent with the younger dryas boundary impact hypothesis postulating a major extraterrestrial impact involving multiple airburst s and and or ground impact s at 12 9 ka

the organization of convection in the rainbands of tropical cyclone laurence abstract a slow moving weak tropical cyclone passed near darwin australia in december 1990 rainbands were observed by a doppler weather radar and a 50 mhz wind profiler for over 24 h the principal bands were seen to be organized on two distinct scales bands of stratiform precipitation formed at a radius of about 100 km from the center of the storm and moved outward at about 6 m s 1 these decayed after they moved past darwin over land a distinct midlevel jet extended along the bands within the bands convective lines formed at regular intervals propagated against and outward with respect to the mean flow and acted as a partial barrier to the radial inflow deep active convection was confined to these lines the vertical motion in the convection showed a distinct acceleration above the freezing level with measured updrafts of up to 10 m s 1 the convection elevated the tropopause height over the rainband it is hypothesized that an inertia gravity wave propagating from near the storm eye was resp

the effects of vertical wind shear on the distribution of convection in tropical cyclones abstract the influence of vertical wind shear on the azimuthal distribution of cloud to ground lightning in tropical cyclones was examined using flash locations from the national lightning detection network the study covers 35 atlantic basin tropical cyclones from 1985 99 while they were over land and within 400 km of the coast over water a strong correlation was found between the azimuthal distribution of flashes and the direction of the vertical wind shear in the environment when the magnitude of the vertical shear exceeded 5 m s 1 more than 90 of flashes occurred downshear in both the storm core defined as the inner 100 km and the outer band region r 100 300 km a slight preference for downshear left occurred in the storm core and a strong preference for downshear right in the outer rainbands the results were valid both over land and water and for depression storm and hurricane stages it is argued that in convectively active tropical cyclones deep divergent circulations oppose the ver

vertical structure of tropical cyclone rainbands as seen by the trmm precipitation radar abstractten years of data from the tropical rainfall measurement mission satellite s precipitation radar trmm pr show the vertical structure of tropical cyclone rainbands radar echo statistics show that rainbands have a two layered structure with distinct modes separated by the melting layer the ice layer is a combination of particles imported from the eyewall and ice left aloft as convective cells collapse this layering is most pronounced in the inner region of the storm and the layering is enhanced by storm strength the inner region rainbands are vertically confined by outflow from the eyewall but nevertheless are a combination of strong embedded convective cells and robust stratiform precipitation both of which become more pronounced in stronger cyclones changes in rainband coverage vertical structure and the amount of active convection indicate a change in the nature of rainbands between the regions inward and outward of a radius of approximately 200 km beyond this radius rainbands consis

secondary wind maxima in hurricanes airflow and relationship to rainbands abstract aircraft flight level data from 787 radial legs in 20 hurricanes are analyzed to identify the composite kinematic structure in the hurricane eyewall and especially with secondary horizontal wind maxima shwm that occur outside the eyewall similar to previous studies analysis of the flight level wind data in the eyewall reveals radial convergence near the radius of maximum wind rmw and the highest frequency of updraft and the largest upward mass transport radially inward of the rmw more than 20 of the flight legs contain substantial secondary horizontal wind maxima of specified strength and length the kinematic structure associated with shwm is similar to that of the hurricane eyewall with radial convergence near the radius of maximum wind and a preferred location for maximum upward motions and upward mass transport just inside the rmw statistical analysis confirms the similarity in characteristics between radial and vertical velocities of the eyewall and near the shwm in addition for

the dynamic response of the hurricane wind field to spiral rainband heating abstract the response of the hurricane wind field to spiral rainband heating is examined by using a three dimensional nonhydrostatic linear model of the vortex anelastic equations diabatic heat sources which are designed in accordance with previous observations of spiral rainbands are made to rotate with the flow around the hurricane like wind field of a balanced axisymmetric vortex common kinematic features are recovered such as the overturning secondary circulation descending midlevel radial inflow and cyclonically accelerated tangential flow on the radially outward side of spiral rainbands comparison of the responses to the purely convective and stratiform rainbands indicates that the overturning secondary circulation is mostly due to the convective part of the rainband and is stronger in the upwind region while midlevel radial inflow descending to the surface is due to the stratiform characteristics of the rainband and is stronger in the downwind region the secondary horizontal wind maxim

shock synthesized hexagonal diamonds in younger dryas boundary sediments the long standing controversy regarding the late pleistocene megafaunal extinctions in north america has been invigorated by a hypothesis implicating a cosmic impact at the llerod younger dryas boundary or ydb 12 900 100 cal bp or 10 900 100 14c years abrupt ecosystem disruption caused by this event may have triggered the megafaunal extinctions along with reductions in other animal populations including humans the hypothesis remains controversial due to absence of shocked minerals tektites and impact craters here we report the presence of shock synthesized hexagonal nanodiamonds lonsdaleite in ydb sediments dating to 12 950 50 cal bp at arlington canyon santa rosa island california lonsdaleite is known on earth only in meteorites and impact craters and its presence strongly supports a cosmic impact event further strengthened by its co occurrence with other nanometer sized diamond polymorphs n diamonds and cubics these shock synthesized diamonds are also associated with proxies indicating major biomass burning charcoal carbon spherules and soot this biomass burning at the younger dryas yd onset is regional in extent based on evidence from adjacent santa barbara basin and coeval with broader continent wide biomass burning biomass burning also coincides with abrupt sediment mass wasting and ecological disruption and the last known occurrence of pygmy mammoths mammuthus exilis on the channel islands correlating with broader animal extinctions throughout north america the only previously known co occurrence of nanodiamonds soot and extinction is the cretaceous tertiary k t impact layer these data are consistent with abrupt ecosystem change and megafaunal extinction possibly triggered by a cosmic impact over north america at 12 900 100 cal bp

time reversal for localization of sources of infrasound signals in a windy stratified atmosphere time reversal is used for localizing sources of recorded infrasound signals propagating in a windy stratified atmosphere due to the convective effect of the background flow the back azimuths of the recorded signals can be substantially different from the source back azimuth posing a significant difficulty in source localization the back propagated signals are characterized by negative group velocities from which the source back azimuth and source to receiver str distance can be estimated using the apparent back azimuths and trace velocities of the signals the method is applied to several distinct infrasound arrivals recorded by two arrays in the netherlands the infrasound signals were generated by the buncefield oil depot explosion in the u k in december 2005 analyses show that the method can be used to substantially enhance estimates of the source back azimuth and the str distance in one of the arrays for instance the deviations between the measured back azimuths of the signals and the know

vertical velocity in oceanic convection off tropical australia abstract time series of 1 hz vertical velocity data collected during aircraft penetrations of oceanic cumulonimbus clouds over the western pacific warm pool as part of the equatorial mesoscale experiment emex are analyzed for updraft and downdraft events called cores an updraft core is defined as occurring whenever the vertical velocity exceeds 1 m s 1 for at least 500 m a downdraft core is defined analogously over 19 000 km of straight and level flight legs are used in the analysis five hundred eleven updraft cores and 253 downdraft cores are included in the dataset core properties are summarized as distributions of average and maximum vertical velocity diameter and mass flux in four altitude intervals between 0 2 and 5 8 km distributions are approximately lognormal at all levels examination of the variation of the statistics with height suggests a maximum in vertical velocity between 2 and 3 km slightly lower or equal vertical velocity is indicated at 5 km near the freezing level virtual t

an axisymmetric view of concentric eyewall evolution in hurricane rita 2005 abstractmultiplatform observations of hurricane rita 2005 were collected as part of the hurricane rainband and intensity change experiment rainex field campaign during a concentric eyewall stage of the storm s life cycle that occurred during 21 22 september satellite aircraft dropwindsonde and doppler radar data are used here to examine the symmetric evolution of the hurricane as it underwent eyewall replacement during the approximately 1 day observation period developing convection associated with the secondary eyewall became more symmetric and contracted inward latent heating in the emergent secondary eyewall led to the development of a distinct toroidal overturning circulation with inertially constrained radial inflow above the boundary layer and compensating subsidence in the moat region properties that are consistent broadly with the balanced vortex response to an imposed ring of diabatic heating outside the primary eyewall the primary eyewall s convection became more asymmetric during

locating far field impulsive sound sources in air by triangulation the firing of a gun generates an acoustic impulse that propagates radially outwards from the source acoustic gun ranging systems estimate the source position by measuring the relative time of arrival of the impulse at a number of spatially distributed acoustic sensors the sound ranging problem is revisited here using improved time delay estimation methods to refine the source position estimates the time difference for the acoustic wavefront to arrive at two spatially separated sensors is estimated by cross correlating the digitized outputs of the sensors the time delay estimate is used to calculate the source bearing and the source position is cross fixed by triangulation using the bearings from two widely separated receiving nodes the variability in the bearing and position estimates is quantified by processing acoustic sensor data recorded during field experiments for a variety of impulsive sound sources artillery guns mortars and grenades imperfect knowledge of the effective speed of sound travel results in bias errors in the source bearing estimates which are found to depend on the orientation of the sensor pair axis with respect to the source direction combining the time delay estimates from two orthogonal pairs of sensors reduces these bias errors

structure and formation of an annular hurricane simulated in a fully compressible nonhydrostatic model tcm4 abstract the structure and formation of an annular hurricane simulated in a fully compressible nonhydrostatic tropical cyclone model tcm4 are analyzed the model is initialized with an axisymmetric vortex on an f plane in a quiescent environment and thus the transition from the nonannular hurricane to the annular hurricane is attributed to the internal dynamics the simulated annular hurricane has all characteristics of those recently documented by knaff et al from satellite observations quasi axisymmetric structure large eye and wide eyewall high intensity and suppressed major spiral rainbands a striking feature of the simulated annular hurricane is its large outward tilt of the wide eyewall which is critical to the quasi steady high intensity and is responsible for the maintenance of the large size of the eye and eyewall of the storm although the annular hurricane has a quasi axisymmetric structure marked low wavenumber asymmetries exist in the eyewall region the formation of the simulated a

reply to blaauw et al boslough daulton gill et al and hardiman et al younger dryas impact proxies in lake cuitzeo mexico blaauw et al 1 take issue with our age depth model for the cuitzeo core they state that no offset for our accelerator mass spectrometry ams 14c dates was quantified that our identification of the cieneguillas tephra is doubtful that we used an outdated calibration model and they object to our rejection of six ams dates in the anomalous zone

distribution and mechanisms of orographic precipitation associated with typhoon morakot 2009 abstractusing a combination of doppler radar observations and rain gauge data this study documents detailed aspects of the orographic precipitation associated with typhoon morakot 2009 rainfall distribution over underlying topographical features and possible physical mechanisms responsible for the observed orographic enhancement are explored the study region constitutes an approximately two dimensional south north oriented orographic barrier with higher wider lower narrower terrain features in its northern southern portions i e the northern and southern barriers upstream conditions were characterized by abundant typhoon background precipitation embedded within strong nearly saturated westerly to west southwesterly oncoming flow the observations show that a wide area of topographically enhanced precipitation and the rainfall maxima were confined to the windward slopes of the northern barrier whereas the strongest rainfall tended to occur near and or slightly downstream of the mountain c

tropical cyclone kinematic structure retrieved from single doppler radar observations part ii the gbvtd simplex center finding algorithm abstract this paper is the second of a series and focuses on developing an algorithm to objectively identify tropical cyclone tc vorticity centers using single doppler radar data the first paper dealt with the formulation of a single doppler radar tc wind retrieval technique the ground based velocity track display gbvtd and the results are verified using analytical tcs it has been acknowledged that the quality of the gbvtd retrieved tc circulation strongly depends on accurately knowing its center position however existing single doppler radar center finding algorithms are limited to estimate centers for axisymmetric tcs the proposed algorithm uses a simplex method to objectively estimate the tc vorticity center by maximizing gbvtd retrieved mean tangential wind when tested with a number of axisymmetric and asymmetric analytical tcs the accuracy of the tc centers estimated by the gbvtd simplex algorithm is 340 m from the true center when adding 5 m s 1 random noise to the doppler velocities

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