diagnosis of the downstream ridging associated with extratropical transition using short term ensemble forecasts abstract the dynamical mechanisms that led to downstream ridging during the extratropical transition et of typhoons tokage and nabi are evaluated using data drawn from a cycling ensemble kalman filter coupled with the weather research and forecasting model wrf during both transitions the ensemble covariances indicate that the 350 k potential vorticity pv at the apex of the ridge which is used to define the ridge structure is proportional to the amount of precipitation along the baroclinic zone to the northeast of the tropical cyclone tc and at some times to the upper tropospheric divergence above the tropical cyclone multivariate regression calculations indicate that the frontal precipitation has the largest impact on the ridge amplitude and area during tokage s transition while the tc divergence has roughly equal impact during some times of nabi s transition the amount of precipitation along the baroclinic zone is modulated by the lower tropospheric frontogenesis and moisture flux on the

early human occupation of a maritime desert barrow island north west australia abstract archaeological deposits from boodie cave on barrow island northwest australia reveal some of the oldest evidence for aboriginal occupation of australia as well as illustrating the early use of marine resources by modern peoples outside of africa barrow island is a large 202 km 2 limestone continental island located on the north west shelf of australia optimally located to sample past use of both the pleistocene coastline and extensive arid coastal plains an interdisciplinary team forming the barrow island archaeology project biap has addressed questions focusing on the antiquity of occupation of coastal deserts by hunter gatherers the use and distribution of marine resources from the coast to the interior and the productivity of the marine zone with changing sea levels boodie cave is the largest of 20 stratified deposits identified on barrow island with 20 m 3 of cultural deposits excavated between 2013 and 2015 in this first major synthesis we focus on the dating and sedimentology of boodie cave to establish the framework for ongoing analysis of cultural materials we present new data on these cultural assemblages including charcoal faunal remains and lithics integrated with micromorphology sedimentary history and dating by four independent laboratories first occupation occurs between 51 1 and 46 2 ka overlapping with the earliest dates for occupation of australia marine resources are incorporated into dietary assemblages by 42 5 ka and continue to be transported to the cave through all periods of occupation despite fluctuating sea levels and dramatic extensions of the coastal plain the changing quantities of marine fauna through time reflect the varying distance of the cave from the contemporaneous shoreline the dietary breadth of both arid zone terrestrial fauna and marine species increases after the last glacial maximum and significantly so by the mid holocene the cave is abandoned by 6 8 ka when the island becomes increasingly distant from the mainland coast

chronology of deformation within the turbidite dominated lachlan orogen implications for the tectonic evolution of eastern australia and gondwana ar ar data from fabric forming white mica in slates syntectonic quartz veins and granitic mylonites constrain the timing of metamorphism deformation and exhumation in the lachlan orogen australia these data also help define the tectonic evolution of the tasmanides during paleozoic time the lachlan orogen formed by the progressive accretion of a thick turbidite fan sequence and volcanic terrains to gondwana during the closing of a small marginal ocean or back arc basin this tectonic setting was similar to the present western and southwestern pacific region accretion of the lachlan orogen to gondwana occurred by closing of the basin system by subduction accretion processes and some translation the process is typified in the western lachlan orogen by a major eastward migrating deformation involving chevron folding and faulting over an eastward propagating decollement melange zone and is recorded by ar ar mica ages ranging from 455 ma in the western part to 390 ma in the eastern part in the central lachlan orogen deformation migrated southwestward from 440 430 to 405 ma away from the high temperature wagga omeo metamorphic complex where deformation metamorphism occurred between 440 and 400 ma in the north 400 ma mica ages record deformation and inversion of structures in the cobar basin in the eastern lachlan orogen ar ar mica dates range from 450 to 340 ma ages of 455 445 ma are yielded by the narooma accretionary complex 405 390 ma ages are found along the major thrust faults bounding high grade metamorphic complexes and 360 340 ma cooling ages are found in the inverted extensional basins e g hill end and related structural zones the ar ar results also document periods of reactivation on early formed structures during later deformation elsewhere in the orogen

large magnitude extensional deformation in the south mountains metamorphic core complex arizona paleomagnetic data are used to test controversial aspects of cordilleran metamorphic core complexes including the original dip of extensional structures origin of the mylonitic front and applicability of rolling hinge models we obtained paleomagnetic data 115 sites 82 accepted for analysis from the weakly deformed interior of a synkinematic footwall intrusive suite and proterozoic footwall rocks of the south mountains metamorphic core complex central arizona these rocks yield dual polarity high unblocking temperature and high to moderate coercivity magnetizations positive baked contact tests indicate that footwall rocks possess primary thermoremanent magnetizations trms or high temperature thermochemical remanent magnetizations tcrms acquired early in their cooling history and during ductile and brittle extensional deformation of structurally higher rocks this is consistent with thermochronologic data indicating rapid synkinematic cooling from crystallization through the range of laboratory unblocking temperatures for the magnetic mineralogy of these rocks between about 22 and 17 5 ma paleomagnetic data are considered as two populations based on the structural asymmetry of the south mountains metamorphic core complex 1 a front side characterized by northeast dipping 10 mylonitic fabrics and brittle extensional structures and 2 a back dipping side characterized by rollover of the mylonitic zone to form a southwest or back dipping 15 mylonitic front comparison of paleomagnetic data from these two sides suggests that the back dipping mylonitic front was synkinematically tilted about 10 down to the southwest the data support a folded shear zone hypothesis for origin of the mylonitic front and the interpretation that footwall rocks possess primary miocene age trms or tcrms a second regional fold test involved data from sites on both flanks of the topographically prominent northeast trending mountain range scale antiform the negative result from this fold test demonstrates that this structure formed early in the extensional history and prior to magnetization acquisition by the plutons we obtained a well grouped footwall grand mean from 62 front side and 20 back dipping site means n 82 d 1 0 i 51 7 k 41 8 95 2 5 we calculated this grand mean with the assumption that front side sites have remained structurally untilted whereas back dipping side sites require removal of 10 of southwest dip this grand mean is statistically indistinguishable 95 confidence level from time averaged miocene expected directions we thus conclude that the current gentle dip of front side mylonites and detachment faults is original therefore both ductile and brittle extensional deformations of the south mountains metamorphic core complex were accommodated along low angle structures dip of 15 our interpretation refutes the widespread applicability of models that predict metamorphic core complexes to represent tilted crustal blocks originally bounded by moderate angle normal faults and does not support rolling hinge models of metamorphic core complex evolution that require a moderate angle ramp

evolving geographic patterns of cenozoic magmatism in the north american cordillera the temporal and spatial association of magmatism and metamorphic core complexes four maps are presented here that show the location and extent of magmatic fields between eastern alaska and northern mexico during the successive time intervals of 55 40 40 25 25 10 and 10 0 ma and four others show the distribution of metamorphic core complexes during the same cenozoic time intervals the maps are based on u s geological survey and canadian cordilleran data bases contining about 6000 isotopic dates and extensive literature review for nearly 60 ma the development of metamorphic core complexes has coincided with the locus of a really extensive and voluminous intermediate composition magmatic fields the association is suggestive of a close link between magmatism and core complex formation namely that magma directly and indirectly lowers the strength of the crust magmatism thus controls the location and timing of core complex formation the stresses responsible may be inherited from mesozoic crustal thickening locally created by uplift and magmatic thickening of the crust and imposed by the global pattern of plate motions and driving forces since the miocene rates of magmatism extension and core complex formation have declined the modern basin and range province is not a suitable model for the situation that existed during major magmatic culminations the singular event of early miocene time the merging of two large magmatic fields extinguishing the laramide magmatic gap explains several disconnected observations the hyperextension episode of the colorado river corridor rapid reorientation of stress patterns across much of western north america and subsequent rapid tectonic movements in california magma triggered breakup of western north america lithosphere coincided with development of the san andreas transform system thermal destruction of the laramide magmatic gap created a california microplate about 22 ma ago that moved rapidly away from north america thus two plate tectonic processes thermal destruction of the lithosphere bridge and northward growth of a transform system interacted to produce miocene and later tectonic patterns and events

late quaternary mega lakes fed by the northern and southern river systems of central australia varying moisture sources and increased continental aridity optically stimulated and thermoluminescence ages from relict shorelines along with accelerator mass spectrometer 14c ages from freshwater molluscs reveal a record of variable moisture sources supplied by northern and southern river systems to lake mega frome in southern central australia during the late quaternary additional lacustrine palynological and terrestrial proxies are used to reconstruct a record that extends back to 105 ka confirming that lakes mega frome and mega eyre were joined to create the largest system of palaeolakes on the australian continent as recently as 50 47 ka the palaeohydrological record indicates a progressive shift to more arid conditions with marked drying after 45 ka subsequently lake mega frome has filled independently at 33 31 ka and at the termination of the last glacial maximum to volumes some 40 times those of today further sequentially declining filling episodes to volumes 25 10 those of today occurred immediately prior to the younger dryas stadial in the mid holocene and during the medieval climatic anomaly southern hemisphere summer insolation maxima are a poor predictor of palaeolake filling episodes an examination of multiple active moisture sources suggests that palaeolake phases were driven independently of insolation and at times by some combination of enhanced southern ocean circulation and strengthened tropical moisture sources

wave packets and life cycles of troughs in the upper troposphere examples from the southern hemisphere summer season of 1984 85 abstract in this paper reanalysis data for the southern hemisphere summer season of 1984 85 produced by the european centre for medium range weather forecasts have been analyzed to examine wave packets and life cycles of baroclinic waves a semiobjective algorithm has been devised to track wave packets it is found that the perturbations in the upper troposphere are dominated by wave packets some of these wave packets can be tracked for several weeks during which they can make up to two trips around the latitude circle the energy life cycles of waves that make up several of these wave packets were analyzed and apart from the incipient waves that started the wave packets most of the subsequent wave development was found to be dominated by convergence and divergence of energy fluxes rather than due to baroclinic or barotropic conversions demonstrating that these wave packets are indeed coherent entities that propagate due to downstream development or dispersion the energy life cycle of the most

a stalagmite record of holocene indonesian australian summer monsoon variability from the australian tropics oxygen isotopic data from a suite of calcite and aragonite stalagmites from cave kni 51 located in the eastern kimberley region of tropical western australia represent the first absolute dated high resolution speleothem record of the holocene indonesianeaustralian summer monsoon iasm from the australian tropics stalagmite oxygen isotopic values track monsoon intensity via amount effects in precipitation and reveal a dynamic holocene iasm which strengthened in the early holocene decreased in strength by 4 ka with a further decrease from w2 to 1 ka before strengthening again at 1 ka to years to levels similar to those between 4 and 2 ka the relationships between the kni 51 iasm reconstruction and those from published speleothem time series from flores and borneo in combination with other data sets appear largely inconsistent with changes in the position and or organization of the intertropical convergence zone itcz instead we argue that the el nino southern oscillation enso may have played a dominant role in driving iasm variability since at least the middle holocene given the muted modern monsoon rainfall responses to most el nino events in the kimberley an impact of enso on regional monsoon precipitation over northwestern australia would suggest non stationarity in the long term relationship between enso forcing and iasm rainfall possibly due to changes in the mean state of the tropical pacific over the holocene

paleomagnetism of middle miocene volcanic rocks in the mojave sonora desert region of western arizona and southeastern california paleomagnetic directions have been obtained from 190 early to middle miocene 12 20 ma mafic volcanic flows in 16 mountain ranges in the mojave sonora desert region of western arizona and southeastern california these flows generally postdate early miocene tectonic deformation accommodated by low angle normal faults but predate high angle normal faulting in the region after detailed demagnetization experiments 179 flows yielded characteristic directions interpreted as original thermal remanent magnetizations trm because of the episodic nature of basaltic volcanism in this region the 179 flows yielded only 65 time distinct virtual geomagnetic poles vgps the angular dispersion of the 65 vgps is consistent with the angular dispersion expected for a data set that has adequately averaged geomagnetic secular variation the paleomagnetic pole calculated from the 65 cooling unit vgps is located at 85 5 n 108 9 within a 4 4 circle of 95 confidence this pole is statistically indistinguishable at 95 confidence from reference poles calculated from rocks of similar age in stable north america and from a paleomagnetic pole calculated from rocks of similar age in baja california the coincidence of paleomagnetic poles from the mojave sonora desert region with reference poles from the stable continental interior indicates that 1 significant vertical axis net tectonic rotations have not accompanied post middle miocene high angle normal faulting in this region 2 there has been no detectable post middle miocene latitudinal transport of the region and 3 long term nondipole components of the middle miocene geomagnetic field probably were no larger than those of the recent 0 5 ma geomagnetic field in contrast paleomagnetic data indicate vertical axis rotations of similar age rocks in the transverse ranges the eastern transverse ranges and the mojave block we speculate that a major structural discontinuity in the vicinity of the southeastward projection of the death valley fault zone separates western areas affected by vertical axis rotations from eastern areas that have not experienced such rotations

to the islands born the research potential of submerged landscapes and human habitation sites from the islands of nw australia this paper focuses on the continental shelf of nw australia and on models for change in littoral and offshore environments of relevance to human occupation over the last 50 kyr major island groups occur on the shelf including the montebello and barrow islands and those of the dampier archipelago at lowest sea level around 22 ka these would have been uplands that then became progressively isolated by subsequent sea level rise by integrating archaeological and zooarchaeological records from excavations on these islands with the geology and geomorphology we interpret palaeoeconomic resource potential in relation to changing sea level and coastline morphology the preservation potential for submerged archaeological sites and features is also assessed current archaeological evidence from these offshore islands indicates that the submerged coastal landscape is likely to have been a potentially rich environment for resources and human occupation even at times of lowest sea level and regional aridity should any exploration of submerged archaeology be carried out in this region it is likely to be rewarding offering unique insights into late pleistocene coastal occupation

the impact of extratropical transition on the downstream flow an idealized modelling study with a straight jet the interaction of a tropical cyclone undergoing extratropical transition et with the midlatitude synoptic scale flow is investigated using full physics numerical experiments with idealized initial conditions the emphasis is on the impact on the midlatitude flow downstream of the et event the midlatitude flow is represented by a balanced straight jet stream as the tropical cyclone approaches the jet a ridge trough couplet and a distinct jet streak form in the upper level flow a midlatitude cyclone develops rapidly downstream of the et system and the further evolution is characterized by downstream baroclinic development based on hovmoller diagrams the upper level development is interpreted as the excitation and subsequent dispersion of a rossby wave train on the potential vorticity gradient associated with the jet the characteristics of this wave train are sensitive to the structure of the jet and to moist processes in the midlatitudes the tropical cyclone undergoing et acts as a sustained forcing for the wave train and the structure of the et system impacts the development most significantly one to two wavelengths downstream of et piecewise inversion of potential vorticity complemented by the partitioning of the flow into its rotational and divergent parts is applied to assess the impact of the et system quantitatively both the cyclonic circulation and the outflow of the tropical cyclone are important contributors to the formation and amplification of the ridge trough couplet the outflow anomaly reduces the eastward motion of the ridge trough couplet significantly and thus promotes phase locking between the tropical cyclone and the upper level pattern copyright 2008 royal meteorological society

southern hemisphere summertime rossby waves and weather in the australian region motivated by recent studies on the significant summertime weather patterns in the australian region the life cycle of summertime transient rossby wave packets in the southern hemisphere is investigated the strength of the interaction between the wave packets and the jet i is defined by the advection of potential vorticity by the divergent part of the wind on the 350 k isentropic surface the magnitude of i is used as the basis for time lagged composites in distinct regions sw chile sw africa over the indian ocean sw australia and over the w pacific the interaction is strongest on the stratospheric side of the jet core although in each case cyclogenesis from a pre existing disturbance in the upper troposphere precedes the generation of the rossby wave packets there are two types of interaction with the jet in the sw chile sw africa and indian ocean cases extratropical cyclogenesis and the associated convection lies on the poleward side of the jet and hence i is positive in the sw australia and w pacific cases extratropical cyclogenesis occurs 3 days earlier than the others and i is negative as it describes the interaction of a downstream propagating rossby wave packet with the subtropical jet in all cases as the cyclones develop the wave activity propagates from low levels to the upper levels of the troposphere and then downstream and equatorwards towards higher values of refractive index the equatorward refraction of the sw australia and w pacific wave packets is accompanied by enhanced tropical convection in the warm conveyor belt of the advancing front

tectonic evolution of the cenozoic olympic subduction complex washington state as deduced from fission track ages for detrital zircons

characteristics of wave packets in the upper troposphere part i northern hemisphere winter abstract gridded data produced by the ecmwf reanalysis project have been analyzed to document the properties of wave packets in the northern hemisphere winter midlatitude upper troposphere based on results from earlier investigations 300 hpa meridional wind variations were chosen for analysis wave packet envelopes were also defined by performing complex demodulation on the wind data the properties of the wave packets are mainly illustrated using time lagged one point correlation maps performed both on and wave packet envelopes the results show that over most regions in the northern hemisphere winter with the exception of the deep tropics and near the aleutian low medium scale waves dominant wavenumber 5 8 exhibit the characteristics of downstream development and occur within wave trains that propagate with eastward group velocities much faster than the phase speeds of individual phases of the waves their group velocity is highly correlated with the local time mean 200 400 hpa wind while the

extratropical transition of tropical cyclones over the western north pacific part i evolution of structural characteristics during the transition process abstract the development of extratropical cyclone structural characteristics that resulted from the extratropical transition of typhoon ty david 1997 and ty opal 1997 over the western north pacific is examined david moved poleward ahead of a midlatitude trough that was moving eastward as the dominant midlatitude circulation feature over the western north pacific during the transition david coupled with the midlatitude trough which led to the evolution of an intense cyclone that became the primary circulation over the north pacific although opal also moved poleward ahead of a midlatitude trough the principal midlatitude feature over the western north pacific was a preexisting stationary cyclone over the kamchatka peninsula during transition opal weakened and became a secondary cyclone to the preexisting primary north pacific cyclone the structural characteristics of the evolving extratropical cyclone with respect to each case are examined in the context of the interaction between a vortex an

magmatism as an essential driving force for formation of active metamorphic core complexes in eastern papua new guinea the d entrecasteaux islands in eastern papua new guinea are composed of a number of active metamorphic core complexes which have been intruded by granodiorite plutons during their formation the plutons do not appear to have been intruded by diapiric processes as previously suggested late relatively undeformed plutons form flat lying bodies which crosscut structural boundaries and are strongly discordant to core complex shear zones granodiorite magmatism and the development of the metamorphic core complexes have occurred in a linear zone which coincides with a zone of thick crust and rugged topography it is proposed that plutonism facilitated deformation in ductile extensional shear zones which resulted in tectonic exhumation of deep crustal rocks and formation of the metamorphic core complexes the source of the plutons is thought to be related to a linear zone of mantle upwelling beneath the islands related to the propagation of the woodlark seafloor spreading center into continental crust it is suggested that a localized heat source of this type which can provide heat and magmatic material to the crust is essential for the development of metamorphic core complexes

exploring sea country through high resolution 3d seismic imaging of australia s nw shelf resolving early coastal landscapes and preservation of underwater cultural heritage abstract almost 2 million square km of australia s continental shelf was flooded following the termination of the last glacial maximum and with it the cultural heritage of the first arrival and coastal occupation of australia beginning some 65 000 years ago in order to prospect for this missing cultural record we must first identify submerged coastal landscapes and landforms that likely provided favourable environments for occupation and resource use however this task is challenged by the sheer size of the australian continental margin to help address this we use industry 3d seismic datasets that cover vast areas of australia s continental shelf to map seafloor bathymetry at high resolution 10 25 m our study focuses an area of 6500 square km on the mid outer shelf regions proximal to barrow island the 3d seismic bathymetry revealed a highly complex and geomorphically mature coastal landscape preserved at depths of 70 75 m below sea level including coastal barrier dunes lagoonal systems tidal flats and estuarine channels based on the depth of the submerged shorelines and reconstructed sea level curves the age range of these coastal landforms is constrained to marine isotope stage 3 57 29 ka which overlaps with the known onset of occupation at barrow island and the wider carnarvon bioregion and the adjacent pilbara such feature preservation has significant geoheritage value but also allows for human behavioural ecology modelling and provides targets for future dating and site survey

volcanism in aboriginal australian oral traditions ethnographic evidence from the newer volcanics province abstract this article collects and presents nineteenth century ethnographic evidence from the newer volcanics province of australia and explores how volcanism was recorded and understood in aboriginal oral traditions it investigates whether aboriginal australian oral traditions can be understood as persistent eyewitness accounts of volcanic eruptions in the newer volcanics province how and what kind of geological and volcanological knowledge was embedded within aboriginal australian oral traditions and considers what value the ethnographic evidence has for understanding both the socio cultural and geological histories of the newer volcanics province

on the dynamics of a storm track abstract an idealized primitive equation model is used to determine the factors controlling the dynamics and maintenance of eddy activity in a storm track the results show that localized regions of enhanced baroclinicity do not necessarily lead to localization of eddy activity by studying the energetics of the storm track it is shown that while baroclinic conversion does indeed correlate with the region of maximum baroclinicity it is the downstream radiation of energy through the ageostrophic geopotential fluxes which acts as a trigger for the development and maintenance of eddy activity over less baroclinic regions extending the region of eddy activity much further downstream from the region of high baroclinicity examples of eddy life cycles are given that show that convergence and divergence of ageostrophic fluxes can dominate baroclinic and barotropic conversion especially in regions with weak baroclinicity factors that may limit the zonal extent of a storm track are discussed evidence of down

superposed local and regional paleostresses fault slip analysis of neogene extensional faulting near coeval caldera complexes yucca flat nevada numerous reduced stress tensors are computed by multiple inversions of 906 temporally and spatially partitioned fault slip data from the yucca flat region in the southwest nevada volcanic field to constrain the neogene paleostress and faulting history and to investigate how the regional tectonic stress field was affected by local caldera magmatism perturbed shallow 400 m pre 11 ma paleostress configurations determined west and northwest of present post 11 ma yucca flat basin existed during mild extensional faulting and are attributed to superposition of transient caldera magmatic stresses on the regional stress field northwest of yucca flat a progressive shift in least principal stress 3 directions near known calderas located 5 15 km to the west occurred under a normal slip stress state during caldera development between about 15 and 13 ma a brief 0 5 m y change to a strike slip stress state occurred at about 13 ma and was accompanied by small offset quasi conjugate strike slip faulting this stress state was most distinct relative to a normal slip state near calderas where stress solutions and fault relations indicate closer affinities to a reverse slip state inferred 11 6 11 45 ma paleostress tensors indicate radial tension associated with either initial caldera collapse or local post collapse topographic modification of the stress field post 11 ma normal slip stress tensors are associated with normal and oblique slip faults that accommodated subsidence and eastward extension of yucca flat basin away from the caldera complexes these tensors do not indicate stress modifications due to residual caldera related effects and thus were used to infer post 11 ma regional stress changes the stress field has rotated as much as 65 clockwise since 11 ma during extensional development of yucca flat basin with most of the rotation and extension occurring before about 8 5 ma results suggest that shallow magmatism and caldera development can strongly alter extensional tectonic stress fields fault patterns and slip directions in the uppermost crust out to distances of roughly two magma chamber radii away from a magma body

radiocarbon evidence for mid late holocene changes in southwest pacific ocean circulation variability in the southwest sw pacific ocean circulation is influenced by the changes in the south pacific subtropical gyre and its western boundary current the east australian current eac the eac plays a significant role in transporting warm well ventilated nutrient poor waters to more temperate higher latitudes recent climate changes associated with eac intensification have led to anomalous warming in the south tasman with implications for marine ecosystems and environment a clear understanding of the significance of these changes requires knowledge of past natural variability here we have reconstructed a 4500 year record of regional sea surface radiocarbon reservoir ages r and local reservoir effects r our results reveal the centennial scale variability over the last 4500 years with r ranges as large as 390 14c yr older r 410 14c yr between 1610 to 1860 a d in our record corresponding to the little ice age suggests a weaker influence of the eac in the south tasman between 4000 and 1900 cal years b p r and r were significantly younger than the modern with values of 170 and 130 14c yr respectively indicating increased eac transport of tropical waters into the south tasman we propose that the large r variability was influenced by strong and abrupt el nino events which punctuated the muted el nino southern oscillation enso period in the mid late holocene and enabled increased westward flow of gyre waters into the sw pacific the strengthening of the eac extension appears to have been a response to the precession modulated enso southern annular mode interactions

interactions of north pacific tropical midlatitude and polar disturbances resulting in linked extreme weather events over north america in october 2007 abstractthis study uses observations and model reanalyses to examine the multiscale processes associated with four high impact extreme weather events ewes over north america during late october 2007 the ewes consisted of wind driven wildfires in california prolonged anomalous cold conditions in mexico linked to two cold surges heavy rainfall in the eastern united states and severe flood producing heavy rainfall in southern mexico the ewes involved a pronounced large scale flow reconfiguration across the north pacific and north america in conjunction with the formation of a high amplitude rossby wave train the flow reconfiguration involved perturbations to the north pacific jet stream linked to polar midlatitude and tropical disturbances including three tropopause level polar disturbances originating over northeastern asia transient extratropical cyclones a diabatic rossby vortex and western north pacific tropical cyclone kajiki eulerian and lagrangian diagnostics indicate that ridge amplifi

the 40ar 39ar thermochronology of the eastern mojave desert california and adjacent western arizona with implications for the evolution of metamorphic core complexes mesozoic thickening and cenozoic extension resulted in the juxtaposition of upper and middle crustal rocks in the eastern mojave desert southeastern california and western arizona the application of 40ar 39ar thermochronology to rocks in this region provides information about the timing and nature of thrusting plutonism metamorphism denudation and detachment faulting the 40ar 39ar ages of 175 to 125 ma from the clipper piute turtle mohave bill williams and hualapai mountains are interpreted to be the result of a middle mesozoic thermal event s caused by crustal thickening the 40ar 39ar data from the clipper and piute mountains suggest that this thermal event was followed by a period of cooling at rates of 1 5 c m y orogenesis culminated during the late cretaceous when rocks exposed in the old woman piute chemehuevi and sacramento mountains attained temperatures 500 c which reset the k ar systems of minerals from proterozoic rocks high grade metamorphism in the old woman mountains area was caused by the intrusion of the old woman piute batholith at 73 1 ma cooling rates following batholith emplacement in the old woman mountains were 100 c m y between 73 and 70 ma and 5 10 c m y from 70 to 30 ma between 65 and 25 ma the entire eastern mojave desert underwent a period of cooling at a rate of 2 10 c m y by 30 ma rocks exposed in the old woman piute marble ship clipper and turtle mountains were below 100 c the 40ar 39ar ages from the sacramento mountains suggest that mylonitization caused by the onset of regional extension occurred at 23 1 ma when extension started in the chemehuevi mountains rocks exposed in the southwestern and northeastern portions of footwall to the chemehuevi detachment fault were at 180 c and 350 c respectively this suggests that the exposed part of the chemehuevi detachment fault initiated at a dip of 5 30 or as a series of higher angle faults that cut to a depth of 10 12 km and were later rotated to their present dip unroofing of the footwalls to detachment faults in the sacramento and chemehuevi mountains resulted in average cooling rates of 10 50 c m y between 22 and 15 ma

the potential for discovery of new submerged archaeological sites near the dampier archipelago western australia abstract the islands of the dampier archipelago preserve a probable 30 000 year archaeological record that reflects the change from a continental to an island environment following post glacial sea level rise the geomorphological history of the dampier archipelago region in combination with preliminary hydrodynamic modelling of past tidal regimes provides the basis for a new model of how the shelf landscape may have developed between the last glacial maximum c 20 ka bp through the holocene marine transgression and up to the present day using first order geomorphological principles an assessment is made of the key late pleistocene and holocene sediment bodies that may preserve archaeological deposits we show that archaeology is most likely to be present in deposits associated with the early phases of inundation of the dampier archipelago dating from around 9 7 ka bp at this time relative sea levels were around 30 m to 15 m which was when coastal configuration was complex and the variety and scale of intertidal and shallow sub tidal environments wide in contrast we anticipate that coastal archaeology older than 12 ka bp when the post glacial sea levels were below 50 m will have been exposed to a phase of faster tidal currents on the continental shelf and hence eroded or poorly preserved our study aims to improve prospection for and later management of the as yet unknown submerged elements of west australia s rich archaeological heritage

tilt and rotation of the footwall of a major normal fault system paleomagnetism of the black mountains death valley extended terrane california paleomagnetic data have been obtained from miocene intrusions including crosscutting mafic and felsic dikes and proterozoic crystalline rocks to evaluate deformation during miocene and younger extension and unroofing of the black mountains death valley california synrift intrusions contain a well defined and at the site level well grouped magnetization interpreted to be of dual polarity the in situ direction of which is discordant in declination and inclination with an expected late cenozoic reference direction the oldest of these intrusions 11 6 0 2 ma gives a magnetite dominated remanent magnetization of high coercivity and high laboratory unblocking temperatures about 550 to 580 c that is interpreted to predate unroofing from midcrustal depths in situ site mean directions of this magnetization are directed toward the west and west northwest with moderate to shallow positive down and negative up inclinations the variation in direction of magnetization particularly inclination with site locality around the turtleback structures along the western flank of the black mountains is interpreted to result from folding of the intrusion after remanence acquisition younger intrusions 8 7 ma generally give magnetizations with inclinations similar to expected miocene values two populations of in situ site means are identified one with southwest declination and negative inclination the other with northward declination and positive inclination a preferred interpretation for footwall deformation involves from oldest to youngest 1 southwest side down tilting of the entire range block of some 20 to 40 to possibly 70 and at least locally folding of the crystalline rocks on a trend parallel to the death valley turtlebacks between 11 6 and 8 7 ma 2 progressive east to west footwall unroofing between 8 7 and ca 6 5 ma and 3 clockwise rotation 50 to 80 of much of the black mountains after the core detached from stable terrane to the west we interpret late rotation of the black mountains as oroflexure related to right lateral shear along the death valley fault zone

vortex vortex interaction between hurricane nadine 2012 and an atlantic cut off dropping the predictability over the mediterranean operational ensemble forecasts for the western mediterranean exhibited high uncertainty while hurricane nadine was moving slowly over the eastern north atlantic in september 2012 the forecasts showed a bifurcation in the track of nadine a significant fraction predicting its landfall over the iberian peninsula and a high spread in the synoptic conditions downstream the forecast uncertainty was a major issue for planning observations during the first special observation period sop1 of the hydrological cycle in the mediterranean experiment hymex clustering the ensemble forecast of the european centre for medium range weather forecasts reveals two scenarios for interaction between nadine and an atlantic cut off which controls both the track of nadine and the synoptic conditions downstream the observed scenario of weak interaction is characterized by nadine moving westward and the cut off moving eastward the cut off then triggers precipitation over the cevennes in southeastern france the contrasting scenario of strong interaction is characterized by nadine and the cut off rotating around each other over the atlantic nadine then either merges with the cut off or makes landfall over the iberian peninsula the interaction between nadine and the cut off mimics the vortex vortex interaction previously observed between two tropical cyclones or two upper level vortices it differs from the usual interaction between a tropical cyclone and a larger trough during extratropical transition a critical distance of about 1000 km between nadine and the cut off distinguishes between the cases of weak and strong interaction in the ensemble forecast shifting the initial position of nadine in meso nh numerical experiments confirms the critical distance and suggests a bifurcation point in the relative position of nadine and the cut off the high forecast sensitivity to the vortex vortex interaction resulted in the lowest predictability over the mediterranean during the whole hymex sop1

episodic caldera volcanism in the miocene southwestern nevada volcanic field revised stratigraphic framework 40ar 39ar geochronology and implications for magmatism and extension the middle miocene southwestern nevada volcanic field swnvf is a classic example of a silicic multicaldera volcanic field in the great basin more than six major calderas formed between 15 and 7 5 ma the central swnvf caldera cluster consists of the overlapping silent canyon caldera complex the claim canyon caldera and the timber mountain caldera complex active from 14 to 11 5 ma and centered on topographic timber mountain locations of calderas older than the claim canyon caldera source of the tiva canyon tuff are uncertain except where verified by drilling younger peralkaline calderas black mountain and stonewall mountain formed northwest of the central swnvf caldera cluster we summarize major revisions of the swnvf stratigraphy that provide for correlation of lava flows and small volume tuffs with the widespread outflow sheets of the swnvf new laser fusion 40 ar 39 ar isotopic ages are used to refine and revise the timing of eruptive activity in the swnvf the use of high sensitivity mass spectrometry allowed analysis of submilligram sized samples with analytical uncertainties of 0 3 1 permitting resolution of age differences as small as 0 07 ma these results confirm the revised stratigraphic succession and document a pattern of episodic volcanism in the swnvf major caldera episodes belted range crater flat paintbrush timber mountain and thirsty canyon groups erupted widespread ash flow sheets within 100 300 k y time spans and pre and post caldera lavas erupted within 100 300 k y of the associated ash flows peak volcanism in the swnvf occurred during eruption of the paintbrush and timber mountain groups when over 4500 km 3 of metaluminous magma was erupted in two episodes within 1 35 m y separated by a 750 k y magmatic gap peralkaline and metaluminous magmatism in the swnvf overlapped in time and space the peralkaline tub spring and grouse canyon tuffs erupted early and the peralkaline thirsty canyon group tuffs and stonewall flat tuff erupted late in the history of the swnvf flanking the central volumetrically dominant peak of metaluminous volcanism magma chemistry transitional between peralkaline and metaluminous magmas is indicated by petrographic and chemical data particularly in the overlapping grouse canyon and area 20 calderas of the silent canyon caldera complex volcanism in the swnvf coincided with the miocene peak of extensional deformation in adjoining parts of the great basin although regional extension was concurrent with volcanism it was at a minimum in the central area of the swnvf where synvolcanic faulting was dominated by intra caldera deformation significant stratal tilting and paleomagnetically determined dextral shear affected the southwestern margin of the swnvf between the paint brush and timber mountain caldera episodes larger magnitude detachment faulting in the bullfrog hills southwest of the central swnvf caldera cluster followed the climactic timber mountain caldera episode postvolcanic normal faulting was substantial to the north east and south of the central swnvf caldera cluster but the central area of peak volcanic activity remained relatively unextended in postvolcanic time volcanism and extension in the swnvf area were broadly concurrent but swnvf area were broadly concurrent but in detail they were episodic in time and not coincident in space

45 610 52 160 years of site and landscape occupation at nawarla gabarnmang arnhem land plateau northern australia we present bayesian modelling on a long sequence of radiocarbon ages from the archaeological site of nawarla gabarnmang central arnhem land plateau northern australia a horizon of wind borne sediments containing flaked stone artefacts and charcoal commencing 45 610 cal bp the young end of the modelled boundary age range which extends beyond the limit of the calibration curve with a median modelled age of 48 500 cal bp signals the onset of aeolian mobilisation of fine sands and silts across the landscape and re deposition within the site at a time synchronous with the first evidence of people this earliest cultural horizon stratigraphic unit 4 contains 509 stone artefacts and is marked by a contemporaneous sedimentary break from underlying culturally sterile sediments consisting of disintegrating roof fall and in situ sandstone and quartzite to overlying culturally rich wind blown sand the new radiocarbon ages and wind blown sediments together provide evidence for the commencement of noticeable landscape burning on the arnhem land plateau c 48 500 cal bp suggesting an intensification of landscape management practices at the summit of the arnhem land plateau some 10 000 e15 000 years after the lowest dense band of artefacts phase 2 at madjedbebe on the floodplains 90 km to the north these results have ramifications for the structure and timing of the spread of people across australia and the extinction of megafauna in sahul

northern hemisphere rossby wave initiation events on the extratropical jet a climatological analysis abstracta climatology of rossby wave initiation rwi events on the northern hemisphere mid latitude jet is compiled by applying an objective rwi identification algorithm to the era interim re analysis dataset in winter rwi events occur most frequently over the northwestern pacific and less often over the north atlantic in summer the total number of rwi events is lower than in winter and the north pacific rwi region shifts towards the tibetan plateau composite analysis of the large scale flow prior to during and after winter north pacific rwi events shows an upstream wave train propagating across asia on the arctic waveguide prior to rwi the composite wave forms on a relatively weak zonal jet streak exhibits a baroclinic structure and is strongly amplified by latent heat release in the warm conveyor belt of a deepening surface cyclone moreover the wave forms in a region of large scale upper level deformation upstream of a pre existing ridge further active tropical convection affects the longit

the steens mountain oregon geomagnetic polarity transition 3 its regional significance study of the variations of direction and intensity of the geomagnetic field as recorded by the miocene lava flows on steens mountain southeastern oregon has resulted in a detailed description of total field behavior during a reversal in polarity in addition to information about the polarity reversal itself the detailed paleomagnetic record includes several thousand years of geomagnetic history preceding and following the polarity transition at 15 5 ma in order to test the feasibility of using this record as a means of correlation in this part of the western united states comparisons are made of reconnaissance and previously published paleomagnetic records obtained from what has been thought to be the steens basalt or rocks of equivalent age despite the fact that many of these earlier studies were not done in detail and were not intended for correlation purposes convincing similarities among some of the records are evident the steens basalt paleomagnetic record does indeed have potential as a correlation tool during this time of widespread basaltic volcanism additionally paleomagnetic data from flows that were sampled in detail yield a middle miocene paleomagnetic pole at 88 3 n 209 0 95 6 3 for the high lava plains of oregon this pole position is statistically indistinguishable from the earth s rotational axis and implies that no tectonic rotation of this region has occurred since these lava flows were erupted data from selected sites within the coeval part of the columbia river basalt group yield a paleomagnetic pole at 88 7 n 171 6 e 95 4 0 the columbia river basalt group pole is statistically indistinguishable from either the rotational axis or from the high lava plains pole these findings indicate no post 20 ma differential rotation between south eastern washington and south central oregon in contrast to previous interpretations

constraints on extension related plutonism from modeling of the colorado river gravity high the colorado river gravity high is a positive gravity anomaly coincident in location with the colorado river extensional corridor a zone of extreme middle tertiary crustal extension in the southern basin and range the high extends for 150 km along the west side of the colorado river and has a magnitude of 10 20 mgal above the regional level the source of this gravity high has previously been interpreted as either mafic intrusion or dense material added to the middle crust via lateral flow during extension detailed modeling of the gravity high is now possible due to acquisition of new gravity data that thoroughly define the shape of the anomaly at and around its highest point the peak of the high is 20 mgal higher than the ambient level of the anomaly and is in the southern sacramento mountains california a small 50 km 2 middle tertiary pluton composed of mixed and mingled diorite and granite crops out in the southern sacramento mountains at the location of the peak of the gravity high surface density measurements indicate that the miocene diorite has the highest density in this area a maximum density of 2 91 g cm 3 and a mean density including measurements of mingled diorite and granite of 2 75 g cm 3 this pluton is interpreted to be the minor surface expression of a larger deeper source for the colorado river gravity high forward modeling of the bouguer gravity data is based on surface structure and density contrasts documented by recent geologic mapping and on interpretations of the deeper levels of the crust from the seismic experiments of pace calcrust and cocorp interpretation of a regional profile crossing the peak of the gravity high yielded several possibilities from which one preferred model was chosen on the basis of geologic data the preferred model is that of intrusion of mantle derived melt which acquired an upward decreasing density distribution due to mixing and mingling with magma derived from the continental crust the magma conduit is linked through the entire crust and shows no sign of offset or decapitation by a detachment fault system in three dimensions the colorado river gravity high can be interpreted as the geophysical signature of an 150 km long 10 to 20 km wide zone of intrusion into the area of maximum crustal extension the magmatic contribution to extension in this region was primarily in the form of large subvertical dike like intrusions rather than sill like or horizontally distributed underplated material the inflated lower middle crust interpreted from seismic data may be due to either 1 lateral material flow into the zone of maximum extension which mixed and mingled with intrusions from the mantle or 2 ponding of some intruded material between the lower and middle crust in either case the ultimate cause of the gravity high is intrusion of mantle derived melt incorporated with melt derived from continental crust which is now exposed as mixed and mingled granite and diorite in the southern sacramento mountains

a phase locking perspective on rossby wave amplification and atmospheric blocking downstream of recurving western north pacific tropical cyclones abstractthe extratropical transition et of tropical cyclones tcs can significantly influence the evolution of the midlatitude flow however the interaction between recurving tcs and upstream u

rossby wave packets on the midlatitude waveguide a review abstractrossby wave packets rwps are rossby waves for which the amplitude has a local maximum and decays to smaller values at larger distances this review focuses on upper tropospheric transient rwps along the midlatitude jet stream their central characteristic is the propagation in the zonal direction as well as the transfer of wave energy from one individual trough or ridge to its downstream neighbor a process called downstream development these rwps sometimes act as long range precursors to extreme weather and presumably have an influence on the predictability of midlatitude weather systems the paper reviews research progress in this area with an emphasis on developments during the last 15 years the current state of knowledge is summarized including a discussion of the rwp life cycle as well as rossby waveguides recent progress in the dynamical understanding of rwps has been based in part on the development of diagnostic methods these methods include algorithms to identify and track rwps

disentangling the impacts of climate and human colonization on the flora and fauna of the australian arid zone over the past 100 ka using stable isotopes in avian eggshell abstract throughout the quaternary the flora and fauna of australia evolved and adapted to the high amplitude low and high frequency climate changes that characterized the ice age cycles however during the last glacial cycle between 120 and 15 ka unprecedented irreversible changes in flora and fauna occurred and in that same interval modern humans established their first firm presence in the landscape disentangling the impacts of the first order trend toward a colder drier planet through the late quaternary from the impacts of human colonization has been challenging from both the chronological and paleoenvironmental perspectives we utilize the stable isotopes of carbon and oxygen preserved in near continuous time series of dromaius emu eggshell from five regions across australia to provide independent reconstructions of ecosystem status and climate over the past 100 ka carbon isotopes are determined by the diet consumed by the female bird whereas oxygen isotopes record the status of local moisture balance in the months prior to breeding together 13 c and 18 o provide ecosystem status and climate from the same dated sample reducing correlation uncertainties between proxies combined with recent improvements in the chronologies of late quaternary shorelines fringing inland lake basins and deflation during arid times these data collectively reaffirm that australia generally became increasingly albeit irregularly drier from the last interglaciation through to the last glacial maximum dromaius eggshell 18 o documents peak aridity between 30 and 15 ka but shows no evidence of exceptional climate change between 60 and 40 ka in contrast dromaius 13 c diet documents an irreversible loss of the majority of palatable summer rainfall related c4 grasses across the australian arid zone between 50 and 45 ka about the same time that the giant megafaunal bird genyornis became extinct and coincident with human dispersal across the continent our data indicate that changes unique to australia occurred between 50 and 45 ka that led to a new climate vegetation relationship and an overall reduction in effective moisture across much of the continent the large summer rainfall dominated lakes of interior australia failed to re fill subsequently despite a wide range of global climate states a full explanation for the mechanisms behind these changes remains elusive but they are almost certainly related to human agency plausible explanations include a change in fire regime resulting from human lit fires a change in fire regime following extinction of megafaunal browsers and or a threshold response to increasing aridity of these the climate change explanation is least likely given the lack of evidence for unprecedented aridity between 60 and 40 ka and the successful adaptation of australian ecosystems to 2 5 ma of similar changes

the extratropical transition of hurricane irene 1999 a potential vorticity perspective extratropical transition et of tropical cyclones is common in all ocean basins where tropical cyclones recurve polewards after the tropical cyclone experiences et a rapid deepening can take place resulting in the development of a very large and deep extratropical cyclone the et of hurricane irene 1999 was an example of such an explosive et irene formed in the caribbean and experienced et as it moved poleward resulting in a low pressure system which deepened 39 hpa in 24 hours according to the met office analyses the extent to which the hurricane was responsible for the explosive extratropical development has been determined by performing met office unified model forecasts from initial states with and without the hurricane the circulation and temperature anomalies associated with the hurricane were removed from the initial state using potential vorticity inversion the moisture anomaly co located with the hurricane core was also removed the results show that an extratropical cyclogenesis event takes place regardless of the presence of the hurricane in the initial conditions however the hurricane makes a significant difference to the track and central mean sea level pressure evolution of the resulting extratropical cyclone when irene was present the track of the extratropical cyclone was more zonal and the cyclone deepening rate was twice as fast as when irene was not present these effects appear to be particularly associated with a negative potential vorticity anomaly and enhanced divergent flow in the region of the upper level outflow of the transforming hurricane rather than with the hurricane vortex results also show that the presence of the hurricane resulted in a significant downstream surface low development in the eastern atlantic copyright 2004 royal meteorological society

reappraisal of sea level lowstand during the last glacial maximum observed in the bonaparte gulf sediments northwestern australia abstract during the last glacial maximum lgm ice volume reached a relative maximum and global temperature was lower than today understanding continental ice volume change requires accurate reconstruction of relative sea level but tectonic uplift and isostatic adjustment effects complicate many records using marine sediment cores from the bonaparte gulf in northwestern australia a so called far field tectonically stable site yokoyama et al 2000 reported that the lgm terminated abruptly at 19 ka with a rapid sea level rise 19 ka event their sea level reconstruction determined the age of the lgm termination but the timing of its inception remained less well constrained partly because the number of radiocarbon analyses was insufficient to clarify lgm duration here we return to the bonaparte gulf and present a new relative sea level that better constrains lgm duration with high resolution radiocarbon dating of a recently recovered marine sediment core water depth 120 m length 583 cm radiocarbon dating of 23 molluscs and 26 bulk organic matter samples together with total organic carbon total nitrogen and stable carbon isotopes provide a record of paleoenvironmental variability in response to sea level change our results indicate that the lgm sea level minimum occurred at 20 8 cal ka bp and the lgm duration was shorter than previously reported

continuous 150 k y monsoon record from lake eyre australia insolation forcing implications and unexpected holocene failure our reconstructed history of lake eyre provides the first continuous continental proxy record of australian monsoon intensity over the past 150 k y this continental record s broad correspondence to the marine isotope record demonstrates that this very large catchment with its hydrology dependent on a planetary scale climate element responds to milankovitch scale climate forcing abrupt transitions from dry phases to wet phases ca 125 and 12 ka coincide with northern hemisphere winter insolation minima rather than southern hemisphere summer insolation maxima indicating that northern hemi sphere insolation exerts a dominant control over the intensity of the australian monsoon stratigraphic and dating uncertainties of other wet phases preclude conclusive correlation to specific insolation signals but within the uncertainties are consistent with northern hemisphere forcing regardless of the hemispheric forcing the low intensity of the early holocene australian monsoon by comparison with the last interglacial and particularly the last high level lacustrine event at 65 60 ka when all forcing elements were modest is an enigma that can be explained by a change in boundary conditions within australia

vertical structure of midlatitude analysis and forecast errors abstract the dominant vertical structures for analysis and forecast errors are estimated in midlatitudes using a small ensemble of operational analyses errors for fixed locations in the central north pacific and eastern north america are selected for comparing errors in regions with relatively low and high observation density respectively results for these fixed locations are compared with results for zonal wavenumber 9 which provides a representative sample of baroclinic waves this study focuses on deviations from the ensemble mean for meridional wind and temperature at 40 n these quantities are chosen for simplicity and because they capture dynamical and thermodynamical aspects of midlatitude baroclinic waves results for the meridional wind show that analysis and forecast errors share the same dominant vertical structure as the analyses this structure peaks near the tropopause and decays smoothly toward small values in the middle and lower troposphere the dominant vertical structure for analysi

a reinterpretation of the timing position and significance of part of the sacramento mountains detachment fault southeastern california a contact previously considered to be part of the sacramento mountains detachment fault sdf exposed in the sacramento mountains metamorphic core complex is reinterpreted as an unconformity between tertiary rhyolite of eagle peak and cataclastically deformed crystalline lower plate rocks this reinterpretation is based on outcrop scale topographic relief and the absence of deformation along the base of the rhyolite even where underlying rocks are severely deformed and altered the rhyolite is dated at about 14 3 ma lower plate rocks of the sdf comprise gneiss intruded by granodiorite tonalite and leucogranite mylonitic fabrics are variably developed in lower plate rocks and are cut by brittle shear zones that contain ultracataclasite and by high and low angle faults upper plate rocks include gneiss nonmylonitic granodiorite tonalite and granite and middle miocene sedimentary and volcanic rocks on the south side of eagle peak a thick ultracataclasite zone dips about 30 west contains subhorizontal hematite stained slickenlines and is interpreted to be part of the sdf system this ultracataclasite zone is unconformably overlain by more gently dipping undeformed 14 3 ma rhyolite of eagle peak the unconformity records unroofing of a domed sdf after a period of 8 to 9 m y of progressive unloading of the lower plate in an evolving extensional shear zone extension on part of the sdf was accommodated by a system of high angle oblique slip faults

the downstream impact of tropical cyclones on a developing baroclinic wave in idealized scenarios of extratropical transition the interaction of a tropical cyclone with a developing baroclinic wave is investigated in an idealized scenario of extratropical transition et the impact of et is examined by comparing and analyzing two numerical baroclinic wave experiments a traditional experiment in which baroclinic development is excited by a localized upper level perturbation on a realistic jet profile and an experiment in which additionally a model tropical cyclone is inserted south of the jet at the initial time et occurs in a wavy upper level flow while baroclinic surface systems are still weak the characteristic direct impact of et on the midlatitude flow is the formation of a distinct jet streak and the amplification of a ridge trough couplet in the adjacent downstream region the subsequent rapid cyclogenesis downstream is a direct consequence of these upper level flow modifications this faster and stronger development constitutes the amplification of the leading edge of downstream development both the upper level wave pattern and the surface development are subsequently amplified in the region further downstream the formation of the ridge adjacent to the intensified downstream cyclone is analyzed in detail to elucidate the next stage in the downstream dispersion of the et impact ridge building in the et scenario exhibits characteristics distinct from those in the life cycle experiment wave breaking feedback from the modified low level frontal structure and diabatic processes all contribute to the high amplitude wave pattern downstream of et the downstream impact of et is highly sensitive to the initial storm location and intensity the considerable amplification of the leading edge found in the reference experiment is the most widespread and rapidly propagating impact we thus speculate that this leading edge represents an optimal location of the midlatitude circulation where et can lead to the most significant impact on the downstream flow copyright 2010 royal meteorological society

downstream development associated with the extratropical transition of tropical cyclones over the western north pacific abstract the movement of a tropical cyclone into the midlatitudes involves interactions among many complex physical processes over a variety of space and time scales furthermore the extratropical transition et of a tropical cyclone may also result in a high amplitude rossby wave response that can extend to near hemispheric scales after an et event occurs over the western portion of a northern hemisphere ocean basin the high amplitude downstream response often forces anomalous midlatitude circulations for periods of days to a week these circulations may then be related to high impact weather events far downstream of the forcing by the et event in this study downstream development following et events over the western north pacific ocean is examined local eddy kinetic energy analyses are conducted on four cases of north pacific tropical cyclones of varying characteristics during et into varying midlatitude flow characteristics during 15 july 30 september 2005 the goal is to examine the impact of e

palaeoenvironmental dynamics and palaeolithic occupation at katoati thar desert india late pleistocene palaeoenvironments in the thar desert india located at the eastern extent of the saharo arabian desert belt have fluctuated considerably as a result of the varying range and intensity of the indian summer monsoon phases of widespread pleistocene aridity are well documented in the thar desert but research focusing on humid proxies is critical to examine how the region may have facilitated population expansions across southern asia at katoati located on the northeast margin of the thar desert the combination of field recording of sediment sections with detailed analyses micromorphology stable isotope loss on ignition magnetic susceptibility and x ray fluorescence from an archaeological site identify a series of hominin occupations during phases of enhanced humidity between 96 and 60 ka a gradient of humidity on the eastern margin of the thar desert during the late pleistocene is identified with the periodic humidity evident at katoati occurring more frequently and with longer duration towards the southern margin this uneven distribution of humidity in the thar desert is likely to have strongly influenced when and where hominin populations could expand into and across the region

developing wave packets in the north pacific storm track developing wave packets in the western north pacific storm track are diagnosed observationally an abrupt upstream edge to baroclinic wave activity over the western north pacific facilitates comparisons between the observational results and previous theoretical predictions on the spatiotemporal evolution of an impulse disturbance results show that surface cyclogenesis events are preceded by a sharply peaked wave packet that originates poleward of the himalaya plateau and develops rapidly across the north pacific to north america composite wave packet structure is broadly consistent with linear theory for idealized models such as eady s the longitude height structure of the mature packet reveals deep growing waves with horizontal wavelengths of approximately 4000 km near the packet peak downstream from the peak amplitude decays exponentially and wavelength decreases approximately linearly to about 2500 3000 km at the leading edge meridional potential vorticity gradients are concentrated near the tropopause in contrast to linear theory the packets show an abrupt upstream edge and no evidence of upstream development as the packet travels through the along stream variations of the pacific jet stream the packet peak and leading edge group velocity vary these accelerations change the packet length and suggest that the pacific jet may act to focus the packets a sample of north atlantic storm track events reveals similar results and suggests that the atlantic storm track is often seeded by wave packets that originate over the western north pacific ocean in contrast atlantic packets refract equatorward and become trapped on the subtropical jet to the south of himalaya plateau suggesting perhaps less potential for seeding disturbances in the pacific storm track

comparison of wave packets associated with extratropical transition and winter cyclones abstractdifferences in the development of wave packets associated with midlatitude cyclones and the extratropical transition et of tropical cyclones in the western north pacific wnp and atlantic basins are diagnosed observationally by compositing climate forecast system reanalysis cfsr data over a 32 yr period and applying the null hypothesis of no difference in the development structure propagation or downstream extent while the development of midlatitude cyclones during the fall august october and winter november march amplifies a preexisting wave packet moving through the midlatitude storm track et is associated with the quasi stationary amplification of the midlatitude flow the et cases involving the interaction of the decaying tc with a preexisting midlatitude trough are associated with a greater downstream amplitude and longer lasting downstream response than et cases that do not involve the interaction with a trough in the wnp et wave packets have greater amplitude than those asso

the role of tropical cyclones in the formation of tropical upper tropospheric troughs abstract tropical upper tropospheric troughs tutts also known as midoceanic troughs are elongated troughs that appear in summer monthly averaged maps of the upper tropospheric flow over the oceans the transient part of these climatological features is composed of tutt cells and their origin is the subject of this study tutt cells often occur to the east of tropical cyclones a nonlinear shallow water model on the sphere was used in a simplified study of the interactions between tropical cyclones and the circumpolar vortex based on the results of these simulations and keeping in mind their limitations it is proposed that dispersion of short rossby wave energy is a possible mechanism to explain the formation of tutt cells to the east of tropical cyclones the model simulations suggest that two types of tutt cells may form to the east of tropical cyclones when embedded in cyclonic or weak anticyclonic shear the trough to the east of the tropical cyclone may broaden resulting in the formation of an

the key role of diabatic outflow in amplifying the midlatitude flow a representative case study of weather systems surrounding western north pacific extratropical transition abstractrecurving tropical cyclones tcs undergoing extratropical transition et may substantially modify the large scale midlatitude flow pattern this study highlights the role of diabatic outflow in midlatitude flow amplification within the context of a review of the physical and dynamical processes involved in et composite fields of 12 western north pacific et cases are used as initial and boundary conditions for high resolution numerical simulations of the north pacific north american sector with and without the tc present it is demonstrated that a three stage sequence of diabatic outflow associated with different weather systems is involved in triggering a highly amplified midlatitude flow pattern 1 preconditioning by a predecessor rain event pre 2 tc extratropical flow interaction and 3 downstream flow amplification by a downstream warm conveyor belt wcb an ensemble of perturbed simulations demonstrates the robustness of these stages beyond earlier studies investigating pres recurv

paleomagnetism of middle proterozoic diabase sheets from central arizona paleomagnetic results from 1090 ma diabase sheets of the southwestern u s a diabase province exposed in central arizona yield two distinct remanent magnetizations herein termed adn and adr in accordance with the findings of previous investigations magnetization adn is well defined and has an in situ mean direction of d 283 3 i 45 1 k 17 7 95 8 7 n 17 independent observations a mean pole after correction of paleomagnetic site means for a net 5 clockwise rotation of the colorado plateau and transition zone is located at 22 7 n 179 3 e k 21 9 a95 7 8 the second magnetization adr gives an in situ mean direction of d 161 1 i 87 5 k 22 2 95 19 9 n 4 independent observations with a poorly defined pole at 37 6 n 247 6 e k 6 5 a95 38 9 rock magnetic and alternating field and thermal demagnetization characteristics indicate the adn and adr magnetizations are both carried by low ti titanomagnetite both magnetizations are interpreted to be primary

large variations in the holocene marine radiocarbon reservoir effect reflect ocean circulation and climatic changes accurate radiocarbon dating of marine samples requires knowledge of the marine radiocarbon reservoir effect this effect for a particular site region is generally assumed constant through time when calibrating marine 14c ages however recent studies have shown large temporal variations of several hundred to a couple of thousand years in this effect for a number of regions during the late quaternary and holocene here we report marine radiocarbon reservoir correction r r for heron reef and moreton bay in southwestern sw pacific for the last 8 ka derived from 14c analysis of 230th dated corals most of our r r for the last 5 4 ka agree well with their modern value but large r r variability of 410 yr from trough to peak with possible decadal centennial fluctuations is evident for the period 5 4 8 ka the latter time interval also has significant variations with similar features in previously published r r values for other sites in the pacific including southern peru northern chile in southeastern se pacific the south china sea vanuatu and papua new guinea with the largest magnitude of 920 yr from se pacific the mechanisms for these large r r variations across the pacific during the mid holocene are complex processes involving 1 changes in the quantity and 14c content of upwelled waters in tropical east pacific tep frequency and intensity of ocean upwelling in the tep and contribution of subantarctic mode water to the upwelled waters which is influenced by the intensity and position of southern westerly winds and 2 variations in ocean circulation associated with climate change la nina el nino conditions intensity of easterly trade winds positions of the intertropical convergence zone and the south pacific convergence zone which control the spreading of the older upwelled surface waters in the tep to the western sites our results imply the need for employing temporal changes in r r values instead of constant modern values for age calibration of holocene marine samples not only for the sw pacific sites but also for other tropical and subtropical sites in the pacific

rossby wave initiation by recurving tropical cyclones in the western north pacific abstractthe interaction of recurving tropical cyclones tcs with midlatitude rossby waves during extratropical transition et can significantly alter the midlatitude flow configuration this study provides a climatological investigation of rossby wave initiation rwi by transitioning tcs in the specific configuration of an initially zonal midlatitude waveguide and elucidates physical processes governing ab initio flow amplification during et recurving tcs interacting with a zonally oriented waveguide in the western north pacific wnp basin from 1979 to 2013 are categorized into cases initiating rossby waves tc rwi or not tc norwi interactions with a zonally oriented waveguide occurred for 22 7 of the recurving tcs and one third of these resulted in tc rwi in the presence of a tc the probability of rwi on a zonally oriented waveguide is 3 times larger than in situations without a tc the occurrence of tc rwi exhibits a seasonality and is relatively more common during boreal summer than in aut

the early occupation of the eastern pilbara revisited new radiometric chronologies and archaeological results from newman rockshelter and newman orebody xxix abstract for over 30 years the radiometric chronologies of newman rockshelter and newman orebody xxix have been central to archaeological discussions on the pleistocene aboriginal occupation of the hamersley plateau and greater pilbara region until 2009 these two sites were heralded as having the oldest evidence of human occupation on the plateau dating to the last glacial maximum lgm 26 20 ka more recently however the excavations at several other rockshelters have shown that ancient aboriginal peoples occupied the hamersley plateau many thousands of years before the onset of the last glacial cycle when regional climatic conditions were wetter and more amenable this paper presents the results of our re excavation of both newman rockshelter and newman orebody xxix our research has resulted in the compilation and analysis of large lithic datasets for each of these sites and the construction of geo chronologies using modern radiometric techniques including ams radiocarbon dating and optically stimulated luminescence dating these new radiometric chronologies and artefact data indicate that both sites were occupied between 45 and 40 ka despite having significant early occupational evidence neither of the rockshelters present strong evidence for sustained or persistent site use during the lgm proper ca 23 19 ka however there is substantial evidence for more routine occupation of these localities during the terminal pleistocene and holocene

a cyclone phase space derived from thermal wind and thermal asymmetry abstract an objectively defined three dimensional cyclone phase space is proposed and explored cyclone phase is described using the parameters of storm motion relative thickness asymmetry symmetric nonfrontal versus asymmetric frontal and vertical derivative of horizontal height gradient cold versus warm core structure via the thermal wind relationship a cyclone s life cycle can be analyzed within this phase space providing substantial insight into the cyclone structural evolution an objective classification of cyclone phase is possible unifying the basic structural description of tropical extratropical and hybrid cyclones into a continuum stereotypical symmetric warm core tropical cyclone and asymmetric cold core extratropical cyclone life cycles are illustrated using 1 navy operational global atmospheric prediction system nogaps operational analyses and 2 5 ncep ncar reanalyses the transitions between cyclone phases are clearly illustrated within the phase space including extratro

relation of deformation and multiple intrusion in the death valley extended region california with implications for magma entrapment mechanism the crystalline core of the black mountains crustal section death valley california exposes a tremendous volume of miocene plutonic rock intruded at a depth of 10 13 km few plutons were intruded above 10 km prior to unroofing by tectonic denudation in the eastern part of the core a brittle detachment fault separates predominantly miocene hanging wall strata from the midcrustal miocene 11 6 and 8 7 ma plutonic complex and early proterozoic basement in the west mylonitic lineations and foliations locally well developed within the 11 6 ma intermediate mafic willow spring pluton are cut by dikes which emanate from an 8 7 ma silicic plutonic complex the younger silicic complex throughout the crystalline core exhibits few ductile deformational structures published thermal and barometric studies from both plutonic bodies indicate similar midcrustal 10 13 km emplacement depths at ambient temperatures just above 300 c the significant difference in densities of these magmas argues against a density control for magma entrapment also the country rock above and below the plutonic complex contains no apparent differences from field observations that would suggest a change in density the depth of entrapment corresponds well with the expected depth for the crustal strength maximum determined from laboratory experiments the similar emplacement depths but contrasting styles of deformation of the two plutonic bodies further suggests that entrapment may have been controlled by a high strength barrier represented by the brittle ductile transition late hypabyssal intrusions and associated volcanism are linked to diachronous rapid unroofing of the range block all show a northwest progression paralleling the regional extension direction thus when migration of magma through the high strength barrier did occur it was apparently related to increased strain rates which allowed magma ascent by fracture exploitation rheological stratification of the crust may have played an important if not major role in trapping magmas in the middle crust in this area

mechanisms for accommodation of miocene extension low angle normal faulting magmatism and secondary breakaway faulting in the southern sacramento mountains southeastern california the colorado river extensional corridor crec accommodated up to 100 crustal extension between 23 and 12 ma the southernmost sacramento mountains core complex lies within this region of extreme extension and exposes a footwall of proterozoic mesozoic and miocene crystalline rocks as well as miocene volcanic and sedimentary rocks in the hanging wall to the regionally developed chemehuevi sacramento detachment fault csdf system new structural u pb zircon ar ar and fission track geochronologic and paleomagnetic studies detail the episodic character of both magmatic and tectonic extension in this region extension in this part of the crec was initiated with tectonic slip along a detachment fault system at a depth between 10 and 15 km magmatic extension at these crustal levels began at 20 19 ma and directly account for 5 18 km of extension 10 20 of total extension in the southern sacramento mountains three discrete magmatic episodes record rotation of the least principal stress direction in the horizontal plane from 55 to 15 over the following 3 myr the three intrusions bear brittle and semibrittle fabrics and show no crystal plastic fabric development the final 3 4 myr of stretching were dominated by amagmatic or tectonic extension along a detachment fault system with extension directions rotating back toward 75 the data are consistent with extremely rapid cooling and uplift of miocene footwall rocks the 19 ma sacram suite was emplaced at a mean pressure of 3 0 kbars and uplifted rapidly to a level in the crust where brittle deformation was manifested by movement on the detachment fault at 16 ma by 14 ma the footwall was exposed at the surface with detritus shed off and deposited in adjacent hanging wall basins

extension in high grade terranes of the southern omineca belt british columbia evidence from paleomagnetism paleomagnetic observations are used to construct a map of structural tilts in metamorphic and plutonic rocks of the southern omineca belt in southeastern british columbia during eocene extension midcrustal rocks were exhumed in footwalls of low to moderate angle normal faults that dip east and west in the eastern and western parts of the study area respectively tilts averaging 30 to 40 are consistent over large areas and generally antithetic to the major faults in the central part of the study area however the eastern half of the coryell pluton is untilted and its western half in the hanging wall of the east dipping kettle river fault is tilted down to the east in the opposite sense to that expected north of the pluton these eastward tilted rocks are juxtaposed against westward tilted rocks to explain the anomalous tilts a major west dipping eocene normal fault arrow lake fault is inferred and a revised kinematic history for the area proposed observations of magnetic polarity 86 normal laboratory unblocking temperatures and isotopic age data suggest that magnetizations in the west were acquired during chron 23n and in the east in chron 23n and or chron 24n unless extension postdated the acquisition of magnetization tilts would not be observed thus it is argued that extension in the west occurred after 50 6 ma and in the east between 51 6 possibly 53 3 and 50 6 ma these time intervals do not correspond to any known global plate reorganization event indicating that the last phase of eocene extension in the southern omineca belt was governed by regional rather than global processes

characteristics of wave packets in the upper troposphere part ii seasonal and hemispheric variations abstract gridded 300 hpa meridional wind data produced by the ecmwf reanalysis project were analyzed to document the seasonal and hemispheric variations in the properties of upper tropospheric wave packets the properties of the wave packets are mainly illustrated using time lagged one point correlation maps performed on based on indices that show the coherence of wave propagation as well as examination of correlation maps schematic waveguides were constructed for the summer and winter seasons of both hemispheres along which waves preferentially propagate with greatest coherence in the summers the waveguides basically follow the position of the midlatitude jets in the northern hemisphere winter the primary waveguide follows the subtropical jet over southern asia into the pacific but there is a secondary branch running across russia joining the primary waveguide near the entrance to the pacific storm track over the atlantic the waveguide passes east southeastward toward north africa then bac

extratropical transition of tropical cyclones over the western north pacific part ii the impact of midlatitude circulation characteristics abstract two characteristic midlatitude circulation patterns labeled northwest and northeast are found to be associated with extratropical transition et of tropical cyclones over the western north pacific ocean although in both cases the tropical cyclone moves poleward ahead of a midlatitude trough the primary midlatitude circulation is either that trough or is a large quasi stationary cyclone to the northeast of the poleward moving tropical cyclone transition into a northwest pattern typically results in the development within 36 h of an intense extratropical cyclone that moves north northeast a tropical cyclone that moves into a northeast pattern enters into strong zonal flow between the primary midlatitude circulation and the subtropical ridge to the southeast these systems move rapidly eastward and do not intensify significantly during the 36 h following transition in part i of this study the et of typhoon ty david 1997 and the et of ty opal 1997 were investigated in terms of the form

a comparison of the downstream predictability associated with et and baroclinic cyclones abstractthe impact of the extratropical transition et of tropical cyclones and baroclinic cyclogenesis in the western north pacific wnp atlantic and southern indian ocean sio basins on the predictability of the downstream midlatitude flow is assessed using 30 years of cases from the global ensemble forecast system gefs reforecast version 2 in all three basins et is associated with statistically larger 500 hpa geopotential height forecast standard deviation sd compared to the forecast climatology the higher sd values originate from where the tc enters the midlatitudes and spread downstream at the group velocity of the associated wave packet of the three basins wnp et is associated with the largest amplitude and longest lasting sd anomalies forecasts initialized 2 4 days prior to the onset of et have larger sd anomalies compared to forecasts initialized during or after the onset of et by contrast the region of positive sd anomaly associated with winter baroclinic cyclones is confined to

late pleistocene and early holocene exploitation of estuarine communities in northwestern australia this contribution synthesizes archaeological studies of human economies from the barrow montebello islands and uses the area s archaeological record to determine the effects of late pleistocene and early holocene sea level rise on regional coastlines at the height of the last glacial maximum lgm australia s north western coast extended much further west than the present day shoreline during subsequent sea level rise the gently prograding continental shelf was inundated and with it nearly all archaeological evidence for coastal occupation the barrow and montebello islands are one of the few exceptions as they corresponded to inland hinterland ranges during the lgm with the coastline lying some 50 km to their west evidence from all late pleistocene and holocene occupation phases of the barrow montebello islands demonstrate that foragers continued to visit the coast and engage in the exploitation of both terrestrial and marine environments during the late pleistocene when the shoreline was 10 15 km away coastal exploitation is seen through the presence of transportable estuarine and rocky shore gastropods by the early holocene when sea levels were within close proximity of the sites there is a marked increase in marine fauna including reef fish estuarine and reef shellfish crustaceans and estuarine crocodile together this suggests that the nearby muddy procumbent coastlines were productive as well as an important component of coastal and hinterland economies

deposition models for chronological records abstract long term sedimentary sequences provide a wealth of useful information for research into the palaeo environment especially in relation to past climate change shorter records provide similar information in many archaeological contexts however if such records are to be used to provide precise timing of events and more critically the relative timing between different records methods are needed to provide accurate and precise age depth models for these sequences given the imprecision of individual calibrated radiocarbon determinations it is necessary to use the information we have about the deposition process to refine our chronologies and also to provide interpolation between dated levels in any sequence even with layer counted chronologies the uncertainties are sometimes hard to quantify this paper outlines a range of bayesian models for deposition which have been implemented in the computer programme oxcal these models can be used to combine information from the sediments themselves with radiocarbon or other direct dating information such models have the potential to integrate information between different records and provide a coherent chronology on which to base environmental or archaeological research