kinematic evolution of the junction of the san andreas garlock and big pine faults california if the san andreas fault with about 300 km of right slip the carlock fault with about 60 km of left slip and the big pine fault with about 15 km of left slip are considered to have been contemporaneously active a space problem at their high angle junctions becomes apparent large crustal masses converge in the area of the junctions as a result of the simultaneous large displacements on the faults we present here a model in which an early straight north northwest trending san andreas deforms to its present bent configuration in response to a westward displacement of crust north of the garlock fault during this deformation the crust north of the garlock in the vicinity of the junction undergoes north south shortening while the fault junction migrates along the trace of the san andreas fault to the southeast relative to its original position as a result of this migration the mojave area is displaced to the east relative to the original junction position we suggest a similar history in mirror image for the big pine fault and the areas of crust adjacent to it

thickness and extent of the subglacial till layer beneath an antarctic paleo ice stream fast flowing ice streams and outlet glaciers currently account for as much as 90 of the discharge from the antarctic and greenland ice sheets although the deformation of subglacial material has been proposed as the mechanism for this rapid motion such sediment is usually hidden under several kilometers of ice marine geophysical records have allowed reconstruction of the three dimensional thickness of the sedimentary bed beneath a large antarctic paleo ice stream for the first time fast flow is indicated by streamlined seafloor lineations that form the surface of a layer of low shear strength unsorted sediment averaging 4 6 m thick rapid motion of the paleo ice stream was a result of subglacial deformation within this layer

precipitation over eastern south america and the south atlantic sea surface temperature during neutral enso periods the dominant mode of coupled variability over the south atlantic ocean is known as south atlantic dipole sad and is characterized by a dipole in sea surface temperature sst anomalies with centers over the tropical and the extratropical south atlantic previous studies have shown that variations in sst related to sad modulate large scale patterns of precipitation over the atlantic ocean here we show that variations in the south atlantic sst are associated with changes in daily precipitation over eastern south america rain gauge precipitation satellite derived sea surface temperature and reanalysis data are used to investigate the variability of the subtropical and tropical south atlantic and impacts on precipitation sad phases are assessed by performing singular value decomposition analysis of sea level pressure and sst anomalies we show that during neutral el nino southern oscillation events sad plays an important role in modulating cyclogenesis and the characteristics of the south atlantic convergence zone positive sst anomalies over the extratropical south atlantic sad negative phase are related to increased cyclogenesis near southeast brazil as well as the migration of extratropical cyclones further north as a consequence these systems organize convection and increase precipitation over eastern south america

late cenozoic tectonics of the east ventura basin transverse ranges california the east ventura basin originated in the middle miocene as a rift system bounded on one side by the oak ridge simi hills structural shelf and on the other side by a granitic ridge parallel to the san gabriel fault this fault began accumulating right slip 10 12 m y ago at a rate of 4 5 9 mm yr depending on whether total slip is 45 or 60 km slowing to about 1 mm yr in the quaternary north of the santa clara river rifting ended prior to deposition of the uppermost miocene lower pliocene towsley formation south of the santa clara river the rift axis shifted southwest toward the oak ridge simi hills shelf as the towsley formation accumulated against a normal fault ancestor of the santa susana fault a change to contractile tectonics occurred in the pliocene with depos tion of the fernando formation when the newhall potrero anticline developed as a monocline above a blind reverse fault the pico anticline to the southeast and the temescal and hopper ranch modelo anticlines to the northwest may have a similar origin tectonic inversion and displacement on the southwest verging santa susana fault began about 0 5 ma based on appearance of locally derived clasts in the upper saugus formation and its equivalents and continues today along with the southwest verging san cayetano fault farther west also active are northeast verging backthrusts occurring in the east ventura basin fold belt and a segment of the san gabriel fault which now acts as a northeast dipping oblique slip reverse fault northeast trending discontinuities and structures divide the present deformation zone into four segments in the hopper canyon segment at the west end of the area in the west ventura basin the san cayetano fault places miocene modelo formation over pliocene pleistocene strata more than 5 km thick largely at maximum burial to the southeast the newhall potrero segment is characterized by north vergent backthrusts within the east ventura fold belt and by southward thrusting of the basin sequence tectonic inversion over the structural shelf on the santa susana fault farther southeast the placerita segment is marked by reverse faulting on both the santa susana fault and the san gabriel fault southeast of the basin in the san fernando valley the sylmar segment contains a thick pli cene pleistocene sequence overridden by basement rocks of the san gabriel mountains as well as the south verging mission hills granada hills and northridge hills fault zones

on the anomalous precipitation enhancement over the himalayan foothills during monsoon breaks an intriguing feature associated with breaks in the indian summer monsoon is the occurrence of intense flood producing precipitation confined to central eastern parts of the himalayan ceh foothills and north eastern parts of india past studies have documented various large scale circulation aspects associated with monsoon breaks however the dynamical mechanisms responsible for anomalous precipitation enhancement over ceh foothills remain unclear this problem is investigated using diagnostic analyses of observed and reanalysis products and high resolution model simulations the present findings show that the anomalous precipitation enhancement over the ceh foothills during monsoon breaks emerges as a consequence of interactions between southward intruding mid latitude westerly troughs and the south asian monsoon circulation in its weak phase these interactions facilitate intensification of mid tropospheric cyclonic vorticity and strong ascending motion over the ceh foothills so as to promote deep convection and concentrated rainfall activity over the region during monsoon breaks mesoscale orographic effects additionally tend to amplify the vertical motions and precipitation over the ceh foothills as evidenced from the high resolution model simulations it is further noted from the model simulations that the coupling between precipitation and circulation during monsoon breaks can produce nearly a threefold increase of total precipitation over the ceh foothills and neighborhood as opposed to active monsoon conditions

3d fold growth in transpression abstract geological folds in transpression are inherently 3d structures hence their growth and rotation behavior is studied using 3d numerical finite element simulations upright single layer buckle folds in newtonian materials are considered which grow from an initial point like perturbation due to a combination of in plane shortening and shearing i e transpression the resulting fold growth exhibits three components 1 fold amplification vertical 2 fold elongation parallel to fold axis and 3 sequential fold growth perpendicular to axial plane of new anti and synforms adjacent to the initial fold generally the fold growth rates are smaller for shearing dominated than for shortening dominated transpression in spite of the growth rate the folding behavior is very similar for the different convergence angles the two lateral directions always exhibit similar growth rates implying that the bulk fold structure occupies an increasing roughly circular area fold axes are always parallel to the major horizontal principal strain axis max i e long axis of the horizontal finite strain ellipse which is initially also parallel to the major horizontal instantaneous stretching axis isa max after initiation the fold axes rotate together with max sequential folds appearing later do not initiate parallel to isa max but parallel to max i e parallel to the already existing folds and also rotate with max therefore fold axes do not correspond to passive material lines and hinge migration takes place as a consequence the fold axis orientation parallel to max is independent of convergence angle and viscosity ratio therefore a triangular relationship between convergence angle amount of shortening and fold axis orientation exists if two of these values are known the third can be determined this relationship is applied to the zagros fold and thrust belt to estimate the degree of strain partitioning between the simply folded belt and the bordering strike slip fault system

evidence for orbitally controlled size variations of the east antarctic ice sheet during the late miocene ocean drilling program site 1165 penetrated drift sediments on the east antarctic continental rise and recovered sediments from a low energy depositional environment the sediments are characterized by prominent alternations between a green to greenish gray diatom bearing hemipelagic facies and gray to dark gray hemiturbiditic facies our investigation of an upper miocene section using high resolution color spectra multisensor core logs and x ray fluorescence scans reveals that sedimentation changes occur at milankovitch orbital frequencies of obliquity and precession we use this finding to derive an astronomical calibrated time scale and to calculate iron mass accumulation rates as a proxy for sediment accumulation rates terrigenous iron fluxes change by as much as 100 during each obliquity cycle this change and an episodic pattern of enhanced ice rafted debris deposition during times of deglaciation provide evidence for a dynamic and likely wet based late miocene east antarctic ice sheet eais that underwent large size variations at orbital time scales the dynamic behavior of the eais implies that a significant proportion of the variability seen in oxygen isotope records of the late miocene reflects antarctic ice volume changes

the overdeepening hypothesis how erosional modification of the marine scape during the early pliocene altered glacial dynamics on the antarctic peninsula s pacific margin abstract a new synthesis of diatom assemblage data from ocean drilling program odp leg 178 suggests that the pacific margin of the antarctic peninsula underwent a transition from a shallow shelf to an overdeepened shelf in the early pliocene this modification of the marine scape was due to a relatively brief interval of erosion begun at 5 2 ma the erosion was caused by high frequency advances of a super inflated antarctic peninsula ice sheet apis the frequent advances of the higher elevation ice sheet were a consequence of abundant moisture delivered to the region as the polar front migrated southward by 5 12 ma ice streams incised foredeepened glacial troughs into basement on the inner shelf sediment eroded from the inner shelf was transported through cross shelf troughs and deposited in large trough mouth fan depocenters on the upper slope overdeepened shelf conditions became widespread as troughs widened and intra trough banks beveled by 4 25 ma trough mouth fan construction ceased and subsequent advances of the apis have been infrequent we propose that the reduced frequency of grounding events signaled the transition to a modern foredeepened and overdeepened shelf we hypothesize that a new glacial dynamic emerged in the early pliocene because overdeepening led to accelerated heat exchange between the ocean and apis in two ways firstly the overdeepened shelf required that a larger area of the grounded ice sheet s marine terminus be in contact with the ocean secondly erosional deepening of the outer shelf was equivalent to lowering a shelf edge sill that permitted frequent and voluminous intrusion of warm circumpolar deep waters that upwell in the region the resultant accelerated melting at the apis marine terminus caused the super inflated apis to deflate on the mainland which further decreased the possibility that grounded ice could advance on the overdeepened shelf

the present and past bottom current flow regime around the sediment drifts on the continental rise west of the antarctic peninsula throughout the last decade large sediment drifts located on the upper continental rise west of the antarctic peninsula were the target of oceanographic measurements bathymetric mapping seismic investigations shallow sediment coring and deep sea drilling by ocean drilling program odp leg 178 these studies concluded that for most of the late neogene and quaternary a generally sw ward directed bottom current affected the deposition on the drifts in particular during glacial periods the deposition was additionally influenced by nw ward directed transport of terrigenous detritus supplied by turbidity currents from the antarctic peninsula continental slope in a recent study however the palaeomagnetic signal of the drift sediments recovered at two odp leg 178 sites 1095 and 1101 was interpreted to provide spatial and directional information on the physical record of the ne ward flowing antarctic circumpolar current acc here we investigate the link between the clockwise flowing acc and the generally sw wards flowing near bottom contour current we show that at the odp leg 178 sites on the western antarctic peninsula continental margin the acc only affects the ocean circulation above ca 1000 m water depth therefore the signal of acc flow might only be archived in the ice rafted debris ird content of the drift sediments however the ird from the leg 178 sites accounts for only a small proportion of the drift sediments and is dominantly of local origin past variability of bottom water flow around the sediment drifts was reconstructed on the basis of seismic studies and clay mineralogical and grain size analyses these reconstructions provide useful information about both downstream direction and velocity changes of the bottom current and point to its sw ward flow along the upper rise during at least the last 9 4 ma

progressive development of the buyuk menderes graben based on new data western turkey oblique and normal fault systems exposed in the buyuk menderes graben bmg region record two successive and independent complex tectonic events the first group tectonic event is defined by an e w extension related to n s contraction and transpression this group is responsible for the development of nw and ne trending conjugate pairs of oblique faults which controlled early middle miocene basin formation between the early middle miocene and plio quaternary strata exists an unconformity indicating a period of folding uplift and severe erosion associated with n s shortening the second group of events was the change in tectonic regime from e w extension to n s extension which controlled the formation of the buyuk menderes graben by three progressive pulses of deformation the first pulse of extensional deformation was initially recorded in the region by the exhumation of the deep part of the menderes massif mm with the development of the e trending buyuk menderes detachment fault bmdf the minimum age of this pulse is constrained by the older plio quaternary fluviatile deposits of the buyuk menderes graben that range in age from the plio pleistocene boundary interval to late pleistocene the second pulse which is marked by the rapid deposition of alluvial deposits initiated the formation of approximately e w trending high angle normal faults synthetic and antithetic to the buyuk menderes detachment fault on the northern margin during holocene times these faults are interpreted as secondary steeper listric faults that merge with the main buyuk menderes detachment fault at depth the third pulse was the migration of the buyuk menderes graben depocentre to the present day position by diachronous activity of secondary steeper listric faults these steeper faults are the most seismically active tectonic elements in western turkey according to the stratigraphic and structural data the n s extension in the buyuk menderes graben region produced a progressive deformation phase with different pulses during its plio quaternary evolution with migration of deformation from the master fault to the hangingwall the formation of diachronous secondary synthetic and antithetic steeper faults on the upper plate of the buyuk menderes detachment fault hence the southward migration of the deformation and of the buyuk menderes graben depocentre should be related to the evolution of detachment in the region the presence of the seismically active splays of secondary faults implies an active detachment system in the region this young plio quaternary n s extension in the buyuk menderes graben may be attributed to the combined effects of the two continuing processes in aegean region the first process is back arc spreading or probably the roll back of african slab below the south aegean arc which seems to be responsible for the change in the stress tensor from e w extension to n s extension the second and later event is the southwestward escape of the anatolian block along its boundary fault that is the north anatolian fault naf

taking apart the big pine fault redefining a major structural feature in southern california 1 new mapping along the big pine fault trend in southern california indicates that this structural alignment is actually three separate faults which exhibit different geometries slip histories and senses of offset since miocene time the easternmost fault along the north side of lockwood valley exhibits left lateral reverse quaternary displacement but was a north dipping normal fault in late oligocene to early miocene time the eastern big pine fault that bounds the southern edge of the cuyama badlands is a south dipping reverse fault that is continuous with the san guillermo fault the western segment of the big pine fault trend is a north dipping thrust fault continuous with the pine mountain fault and delineates the northern boundary of the rotated western transverse ranges terrane this redefinition of the big pine fault differs greatly from the previous interpretation and significantly alters regional tectonic models and seismic risk estimates the outcome of this study also demonstrates that basic geologic mapping is still needed to support the development of geologic models

clustering of synoptic activity by indian summer monsoon intraseasonal oscillations 1 active and break phases of the indian summer monsoon are characterized by enhancement and decrease of precipitation over the monsoon trough region using genesis data of monsoon low pressure systems lps and circulation data for the period 1954 to 1993 it is shown that the frequency of occurrence of lps is nearly 3 5 times higher in the active phase of monsoon as compared to the break phase in addition the tracks of these synoptic systems are also strongly spatially clustered along the monsoon trough during the active phase of the monsoon the enhanced decreased frequency of occurrence of lps during active break phases is due to modulation of meridional shear of zonal winds and cyclonic vorticity along the monsoon trough by the intraseasonal oscillations iso

margin architecture reveals the transition to the modern antarctic ice sheet ca 3 ma seismic reflection data collected primarily on the continental slope of the pacific margin of the antarctic peninsula after drilling ocean drilling program odp leg 178 allow us to date a regional change in the style of margin accretion to ca 3 ma late pliocene deep erosion of continental shelf and slope which likely included the emplacement of a megadebris flow deposit was followed by prominent growth of steep relatively stable continental slope prograding wedges while the deep distal margin sedimentation rate was significantly reduced a review of the available stratigraphy from deep sea drilling project odp drilling and correlation with available seismic stratigraphic information allowed us to recognize comparable changes in terms of age and trends in continental margin evolution in several places around antarctica we argue that this late pliocene architectural change of the antarctic margin reflects a change in the texture and water content of the sediment delivered by the antarctic ice sheet following the transition from wet to dry based ice regimes this circum antarctic change coincides with the late pliocene ca 3 ma global cooling and is proposed as the marker event of the transition to the modern cold polar dry based antarctic ice sheet

forecasting of scatterometer derived wind fields in the north indian ocean with a data adaptive approach 1 a combination of genetic algorithm ga and empirical orthogonal function eof analysis has been employed to forecast satellite scatterometer observed surface winds in the north indian ocean the eofs are used to compress the major part of the spatial variability into a few eigenmodes the temporal variability is contained in the corresponding principal components pc which have been subjected to singular spectrum analysis for filtering out the random part forecast of the deterministic part has been carried out using ga with lead times varying from 1 to 4 days the entire analysis has been done separately for the zonal and meridional winds finally predicted wind fields have been generated as linear combinations of the spatial eigenmodes weighted by the predicted pcs forecast quality has been evaluated by comparing with an independent validation data set as well as with buoy data the performance of the algorithm has been found to be quite encouraging

mid late pleistocene glacimarine sedimentary processes of a high latitude deep sea sediment drift antarctic peninsula pacific margin the effects of glaciation on sediment drifts is recognised from marked sedimentary facies variation in deep sea cores taken from the continental rise of the antarctic peninsula pacific margin nineteen sediment cores were visually described logged for magnetic susceptibility and x radiographed about 1000 analyses were performed for grain size clay minerals and biostratigraphy foraminifera nannofossils and diatoms four sediment types associated with distinct sedimentary processes are recognised based on textural compositional analysis 1 hemipelagic mud forms the bulk of the interglacial sediment and accumulated from the pelagic settling of bioclasts and ice rafted wind transported detritus 2 terrigenous mud forms the bulk of the glacial sediment and accumulated from a combination of sedimentary processes including turbidity currents turbid plumes and bottom current reworking of nepheloid layers 3 silty deposits occurring as laminated layers and lenses represent the lateral spillout of low density turbidity currents 4 lastly glacial interglacial gravelly mud layers derive from settling of ice rafted detritus five depositional settings are interpreted within sediment drift 7 each characterised by the dominance interaction of one or several depositional processes the repetitive succession of typical sedimentary facies is inferred to reflect a sequence of four climatic stages glaciation glacial deglaciation and interglacial each one characterised by a distinctive clay mineral assemblage and bioclastic content variations in clay mineral assemblage within interglacial stage 5 core sed 06 suggest minor colder climatic fluctuations possibly correlatable with substages 5a to 5e

environmental magnetism of antarctic late pleistocene sediments and interhemispheric correlation of climatic events abstract recent developments in paleomagnetism and environmental magnetism provide new tools for the detailed correlation of climatically induced magnetic mineralogy changes in sedimentary sequences studies of these changes contribute to the reconstruction of climate history for the glacial interglacial cycles of the late pleistocene and to the delineation of the range of natural variability for global climate during the past hundred thousands years here we show that sharp coercivity minima observed in fine grained sediments from the continental rise of the western antarctic peninsula correlate to the major rapid cooling events of the northern atlantic heinrich layers we interpret such an environmental magnetic signal in terms of variations in deep sea diagenetic processes of sulfide formation which reflect changes in the input of detrital organic matter controlled by sea ice extent with the inherent uncertainties in age controls the sedimentary paleoclimatic markers of the two hemispheres are almost contemporaneous but interhemispheric time lags or leads of the order of 1 2 kyr such as those recently reported from the greenland and antarctic ice cores are also compatible with the data

seismic stratigraphy of the antarctic peninsula pacific margin a record of pliocene pleistocene ice volume and paleoclimate multichannel seismic profiles across the pacific margin of the antarctic peninsula show a series of oblique progradational sequences these sequences exhibit a variety of unusual characteristics that suggest they were produced by the action of ice sheets grounded out to the shelf edge at times of glacial maximum reflection events from deeper stratigraphic levels followed down the continental slope and onto the rise overlie ocean crust of known age showing that at least eight such glacial sequences have been deposited within the past 6 m y similar groundings have probably occurred on most antarctic margins but the depositional record is particularly well preserved at this margin because of pliocene pleistocene thermal subsidence neogene global sea level fluctuations have been attributed to changes in volume of continental ice sheets the depositional sequences on the pacific margin of the antarctic peninsula are thought to record west antarctic ice sheet fluctuations directly further investigation of these sequences would assess the relation between fluctuations in ice volume and the low latitude record of global sea level change

correlation of late miocene to early pliocene sequences between the mediterranean and north atlantic ocean drilling program odp site 982 in the north atlantic contains a complete latest miocene to early pliocene section that was tuned to the astronomical timescale by correlating the record of gamma ray attenuation gra bulk density to summer insolation at 65 n and the benthic 18o signal to orbital obliquity for the interval from 4 6 to 7 5 ma the astronomical tuning of the site 982 record permits a direct bed to bed correlation to the cyclostratigraphy of messinian sections in the mediterranean krijgsman et al 1999a 2001 the benthic 18o signal at site 982 records a latest miocene glacial period that lasted from 6 26 to 5 50 ma and consisted of 18 glacial to interglacial oscillations that were controlled by the 41 kyr cycle of obliquity although the intensification of glaciation at 6 26 ma may have contributed to the restriction of the mediterranean it preceded the depositional onset of the lower evaporite unit at 5 96 ma by some 300 kyr the transition from stage tg12 to tg11 at 5 5 ma marks the end of the latest miocene glacial period and precedes the miocene pliocene boundary by 170 kyr although benthic 18o values are relatively low and 18o of bulk carbonate reaches a minimum at the miocene pliocene boundary at 5 33 ma there is no single event that would indicate deglaciation and sea level rise as the cause of the reflooding of the mediterranean we conclude that glacioeustatic changes alone were not responsible for either the start or end of evaporite deposition during the messinian suggesting that tectonic or local climate changes in the mediterranean region were the dominant cause s

repeated advance and retreat of the east antarctic ice sheet on the continental shelf during the early pliocene warm period abstract diatom analysis of a sediment core recovered at iodp site u1358 on the continental shelf off the adelie coast indicated that the lower section of the core contained an assemblage dating back to the thalassiosira innura zone of the lower pliocene that ranges from 4 2 to 5 12 ma based on lithological descriptions at both a macro and micro scale of this early pliocene part of the core four facies were interpreted from the diamictons representing the progressive advance and retreat of the grounding line over the site facies 1a and 1b contain a distinct directional signal from the orientation of the a axis of clasts with several phases of fabric development along with both brittle and ductile deformation features that are common in sediments that have been subglacially deformed facies 1c and 1d are finely laminated and were deposited in open marine conditions the four facies within the depositional model provide for the first time direct evidence for ice advancing across the shelf adjacent to the wilkes subglacial basin on at least four occasions separated by three periods of open marine conditions indicating retreat of grounded ice inland of the site during a warmer than present early pliocene the times of open marine conditions are correlated with previous findings from the neighbouring rise sites that also indicated an oscillating ice margin this has significant implications because firstly it suggests a dynamic east antarctic ice sheet eais that is probably far more sensitive to climatic and oceanic forcing even during relatively short time periods than had previously been thought secondly it suggests that proxies used to interpret the advance and retreat of the grounding line from the rise can be linked with direct evidence of grounding line migration from the shelf it also has important implications for the future behaviour and sensitivity of the eais under present continuing warming conditions together with results from the rise this paper provides a crucial ice extent target for a new ice sheet model of this region during the pliocene

role of orography diurnal cycle and intraseasonal oscillation in summer monsoon rainfall over the western ghats and myanmar coast abstractrainfall over the coastal regions of western india western ghats wg and myanmar arakan yoma ay two regions experiencing the heaviest rainfall during the asian summer monsoon is examined using a tropical rainfall measuring mission trmm precipitation radar pr dataset spanning 16 years rainfall maxima are identified on the upslope of the wg and the coastline of ay in contrast to the offshore locations observed in previous studies continuous rain with slight nocturnal and afternoon evening maxima occurs over the upslope of the wg while an afternoon peak over the upslope and a morning peak just off the coast are found in ay resulting in different locations of the rainfall maxima for the wg upslope and ay coastline large rainfall amounts with small diurnal amplitudes are observed over the wg and ay under strong environmental flow perpendicular to the coastal mountains and vice versa composite analysis of the boreal summer intraseasonal oscillation bsiso shows that the rain an

predicting wind field in the bay of bengal from scatterometer observations using genetic algorithm 1 a technique based on genetic algorithm ga is applied for predicting wind field in the bay of bengal bob using satellite scatterometer observations empirical orthogonal function eof analysis is used for compressing the spatial variability into a set of eigenmodes the time series of each principal component pc is subjected to singular spectrum analysis ssa and ga is applied to the resulting filtered time series the forecast pcs are weighted by the spatial eigenmodes for computing forecast wind fields predictions made up to 5 days in advance are found to be superior to forecast by persistence method

assessing the precision in loading estimates by geodetic techniques in southern europe summary this paper investigates the precision of the estimation of geophysical fluid load deformation computed from grace space gravity gps vertical displacement and geophysical fluids models global circulation models gcms for ocean atmosphere and hydrology using the three cornered hat method this method allows the estimation of the variance of the errors of each technique when the same quantity is monitored by three instruments with independent errors appliedonanetworkofstations severalpointsofviewcanbeconsidered thetechnique level inordertodeterminetheerrorofeachtechnique grace gpsandgcms thesolution level allowingtocomparetheprecisionofthesametechniquewhendifferentstrategies models are used and the station level in order to emphasize local anomalies and geographical patterns in particular our results show a precision of the loading vertical displacement at the level of 1 mm when using grace or the fluid models and of 2 mm using gps we do not find significant differences between the precision of different solutions of the same techniques even when there are strong differences in the data processing

three stage evolution of the los angeles basin southern california we propose that an episode of transtension dominated development of the los angeles basin area from 12 to 6 ma following middle miocene transrotation and prior to the modern transpressional regime transtension resulted from the releasing bend of the san gabriel chino hills cristianitos fault which acted as the primary transform boundary in southern california during this episode such an interpretation implies that significant transform motion did not occur on the southern san andreas fault prior to 6 ma and that the gulf of california has opened primarily since 6 ma we propose a three stage model for evolution of the los angeles basin and vicinity within the evolving transform fault system transrotation 18 12 ma transtension 12 6 ma and transpression 6 0 ma timing of these stages correlates with microplate capture events which occurred during conversion from a convergent margin to a transform margin

predicting wave heights in the north indian ocean using genetic algorithm 1 the present work reports the development of a nonlinear technique based on genetic algorithm ga for the prediction of wave heights in the north indian ocean time series observations of surface wind speed and significant wave height at three locations in the arabian sea as and the bay of bengal bob have been used for developing and testing the technique the predictions have been compared with persistence forecasts and it has been found that the prediction by ga is always superior to persistence forecast and thus represents a net information gain the predicted wave heights have been found to be consistent with the results obtained with autocorrelation analysis applied on the respective time series of wave heights

holocene to pliocene tectonic evolution of the region offshore of the los angeles urban corridor southern california 1 quaternary tectonism in the coastal belt of the los angeles urban corridor is diverse in this paper we report the results of studies of multibeam bathymetry and a network of seismic reflection profiles that have been aimed at deciphering the diverse tectonism and at evaluating the relevance of published explanations of the region s tectonic history rapid uplift subsidence in basins folds and thrusts extensional faulting and strike slip faulting have all been active at one place or another throughout the quaternary period the tectonic strain is reflected in the modern physiography at all scales los angeles la basin has filled from a deep submarine basin to its present condition with sediment impounded behind a large sill formed behind uplifts near the present shoreline newport trough to the south southeast of la basin also accumulated a large volume of sediment but remained at midbathyal depths throughout the period there is little or no evidence of quaternary extensional tectonism in either basin although as much as 6 km of subsidence which mainly occurred by sagging has been recorded in places since the middle miocene the uplifts include folded and thrust faulted terranes in the palos verdes hills and the shelves of santa monica and san pedro bays the uplifted areas have been shortened in a southwest northeast direction by 10 or slightly more and some folds are reflected in the bathymetry two large adjacent midbathyal basins santa monica and san pedro show strong evidence of subsidence and slight west northwest extension 10 during the same time folding was taking place in the uplifts the tectonic boundaries between uplifts and basins are folded normal faulted reverse faulted and strike slip faulted depending on location the rapid quaternary uplift and subsidence along with the filling of la basin have produced a reversal in the regional physiography in the early pliocene la basin was a submarine deep palos verdes and the shelves comprised a northeast basin slope and the present offshore basins and catalina island formed an emergent or shallowly submerged shelf since extensional compressional and lateral strains are all locally in evidence simple notions that this part of southern california underwent a change from miocene transtension to quaternary transpression fail to explain our observations

relationship between continental rise development and palaeo ice sheet dynamics northern antarctic peninsula pacific margin abstract acquisition of swath bathymetry data west of the north antarctic peninsula nap between 63 s and 66 s and its integration with the predicted seafloor topography of smith and sandwell global seafloor topography from satellite altimetry and ship depth soundings science 277 1956 1962 reveal the links between the continental rise depositional systems and the nap palaeo ice sheet dynamics the nap pacific margin consists of a wide continental shelf dissected by several troughs tens of kilometres wide and long the biscoe trough which has been almost entirely surveyed with multibeam sonar shows spectacular fan shaped streamlining sea floor morphologies revealing the presence of ice streams during the last glacial maximum in the study area the continental rise comprises the six northernmost sediment mounds of the nap pacific margin and the canyon channel systems between them these giant sediment mounds have developed since the early neogene by southwest flowing bottom currents which have redistributed along the margin the fine grained component of the turbiditic currents flowing down canyon channel systems the widespread evidence of shallow slope instability within the sediment mounds has been identified from both swath bathymetry and topographic parametric sonar seismic reflection profiles bathymetric data show that the heads of all the rise canyon channel systems coincide geographically with the mouths of the major glacial troughs on the continental shelf edge this suggests a close genetic link between these morphological features and allows considering a glacio sedimentary model for the western nap outer margin seascape development this model considers the availability of depositional space on the continental rise as the limiting factor for mound development the depositional space in turn is controlled by the spacing between glacial maxima shelf edge reaching ice streams this model takes into account both glacial and interglacial scenarios and gives new insights on evaluating the palaeoenvironmental record of the continental rise sediment mounds

predicting extreme phases of the indian summer monsoon abstract extreme active and break phases of the indian summer monsoon ism often bring about devastating floods and severe draughts here it is shown that these extreme phases exhibit distinctive precursory circulation conditions in both the tropics and extratropics over a range of antecedent periods the extremely active monsoon over northern india is preceded by a strengthening of the upper tropospheric central asian high and enhancement of the tropical convection over the equatorial indian ocean and the south china sea the concurrent buildup of the anomalous high over central asia and the arrival of tropical convection over northern india increase the likelihood of occurrence of a heavy rainy period there similarly the concurrent anomalous low over central asia and the arrival of suppressed convection originating from the equatorial indian ocean and the south china sea precede extremely strong monsoon breaks over northern india two predictors can be used to predict the extreme active break phases

nature of the antarctic peninsula ice sheet during the pliocene geological evidence and modelling results compared abstract in this paper we examine the nature of the pliocene antarctic peninsula ice sheet by comparing the terrestrial and marine geological records of the antarctic peninsula and surrounding sea floor with estimated net snow accumulation in the region derived from numerical palaeoclimate model experiments pliocene geological data and our new modelling results are consistent and mutually supportive in suggesting that an ice sheet was present even during the warmest episodes of the pliocene the combined results suggest that the ice sheet in the antarctic peninsula is more robust to globally warmer conditions than is generally assumed at least up to the climatic limits examined in our study

insights from low temperature thermochronometry into transpressional deformation and crustal exhumation along the san andreas fault in the western transverse ranges california 1 the san emigdio mountains are an example of an archetypical transpressional structural system bounded to the south by the san andreas strike slip fault and to the north by the active wheeler ridge thrust apatite u th he and apatite and zircon fission track ages were obtained along transects across the range and from wells in and to the north of the range apatite u th he ages are 4 6 ma adjacent to the san andreas fault and both u th he and fission track ages grow older with distance to the north from the san andreas the young ages north of the san andreas fault contrast with early miocene u th he ages from mount pinos on the south side of the fault restoration of sample paleodepths in the san emigdio mountains using a regional unconformity at the base of the eocene tejon formation indicates that the san emigdio mountains represent a crustal fragment that has been exhumed more than 5 km along the san andreas fault since late miocene time marked differences in the timing and rate of exhumation between the northern and southern sides of the san andreas fault are difficult to reconcile with existing structural models of the western transverse ranges as a thin skinned thrust system instead these results suggest that rheologic heterogeneities may play a role in localizing deformation along the big bend of the san andreas fault as the san emigdio mountains are compressed between the crystalline basement of mount pinos and oceanic crust that underlies the southern san joaquin valley

geographical distribution of variance of intraseasonal variations in western indochina as revealed from radar reflectivity data abstract this study reveals remarkable differences in the geographical distribution of variance between two types of intraseasonal variations in daily mean radar reflectivity data in the western part of the indochina peninsula in this region the downa range lies parallel to the coast and separates the inland region from the coastal region the 30 60 day variation of reflectivity factor dominates most of the coastal region while its variance in the inland region is less than that of background red noise with the same frequency band horizontal gradients in the variance are largest over the range implying that the mountain range plays a significant role in the geographical contrast correlation analysis with reanalysis data shows that the variation only in the coastal region is associated with a synoptic scale zonal wind anomaly with the same time scale suggesting the importance of an orographic rainfall process that brings a large amount of precipitation only to the windward side of the downa range i

middle tertiary extension recorded by lacustrine fan delta deposits plush ranch basin western transverse ranges california abstract the plush ranch formation upper oligocene and lower miocene consists of more than 1800 m of nonmarine sedimentary and volcanic rocks that record the history of an extensional basin referred to here as the plush ranch basin distinctive depositional facies provenance and sediment transport directions along each basin margin suggest an asymmetric basin shape that is consistent with a half graben origin the northern basin margin consists of sandstone dominated alluvial plain deposits 0 1 1 5 m thick normally graded lenticular sandstone beds small deltaic sequences 1 2 m thick were formed where these alluvial systems flowed southward into a lake lenses of massive boulder rich granitic breccia that represent rockslide deposits derived from a nearby northern granitic provenance nterfinger with the alluvial plain facies in contrast to the northern margin the southern basin margin is represented by coarse grained fan delta deposits matrix and clast supported lenticular conglomerate beds 0 2 5 m thick with interbedded trough cross bedded pebbly sandstone represent braided stream and flood flow and or noncohesive debris flow deposits of alluvial fans that drained a highland area to the south the alluvial fan deposits interfinger to the north with several types of subaqueous sediment gravity flow facies including turbidite sandstone beds and matrix supported debris flow conglomerate each of the basin margin depositional systems grades basinward and to the east into lacustrine deposits that include organic rich dark shale evaporite and limestone the lacustrine deposits represent the central and eastern parts of the plush ranch basin which received little coarse siliciclastic sediment basalt deposits that are at least 50 m thick in the west and thicken eastward are interbedded mainly with the lacustrine facies the southern margin of the plush ranch basin formed along a north dipping normal slip fault along which dip separation increased toward the southwest the northern margin developed on the tilted hanging wall block of this fault this fault was later reactivated in post middle miocene time as the present left lateral strike slip big pine fault the plush ranch is one of several extensional and transtensional basins that formed in southern california and western arizona about 25 20 ma as a response to the change from a convergent to a strikeslip tectonic regime along western north america

influence of the madden julian oscillation on wintertime surface air temperature and cold surges in east asia 1 the variations of wintertime surface air temperature sat and the occurrences of cold surges over east asia in association with the madden and julian oscillation mjo are examined the mjo is defined as a combination of the two leading empirical orthogonal function modes of 850 and 200 hpa zonal winds and outgoing longwave radiation in the tropics the spatial pattern and magnitude of sat anomalies over east asia significantly change with respect to mjo phases composite analysis reveals that the mjo sat relationship is mainly affected by strong temperature advection in the lower troposphere in addition occurrences of cold surges are identified using objectively determined synoptic criteria and their relation to the mjo is analyzed most extreme cold surges occur when the mjo convection center is located over the indian ocean and it is suggested that mjo induced circulation anomalies may reinforce the amplification of normal cold surges to extreme cold surges

monsoons itczs and the concept of the global monsoon earth s tropical and subtropical rainbands such as intertropical convergence zones itczs and monsoons are complex systems governed by both large scale constraints on the atmospheric general circulation and regional interactions with continents and orography and coupled to the ocean monsoons have historically been considered as regional large scale sea breeze circulations driven by land sea contrast more recently a perspective has emerged of a global monsoon a global scale solstitial mode that dominates the annual variation of tropical and subtropical precipitation this results from the seasonal variation of the global tropical atmospheric overturning and migration of the associated convergence zone regional subsystems are embedded in this global monsoon localized by surface boundary conditions parallel with this much theoretical progress has been made on the fundamental dynamics of the seasonal hadley cells and convergence zones via the use of hierarchical modeling approaches including aquaplanets here we review the theoretical progress made and explore the extent to which these advances can help synthesize theory with observations to better understand differing characteristics of regional monsoons and their responses to certain forcings after summarizing the dynamical and energetic balances that distinguish an itcz from a monsoon we show that this theoretical framework provides strong support for the migrating convergence zone picture and allows constraints on the circulation to be identified via the momentum and energy budgets limitations of current theories are discussed including the need for a better understanding of the influence of zonal asymmetries and transients on the large scale tropical circulation

modulation of station rainfall over the western pacific by the madden julian oscillation 1 rainfall data from 140 stations in the pacrain network in the tropical western pacific are analysed to assess the signal due to the madden julian oscillation mjo during northern winter the station rainfall difference between the wet and dry phases of the mjo is up to 6 mm day 1 compared to the climatological mean value of 12 mm day 1 the anomalies have a strong spatial coherence with over 80 of the individual point station anomalies having the same sign as the large scale rainfall anomaly as determined by the mainly satellite derived cmap rainfall product

flow dynamics and till genesis associated with a marine based antarctic palaeo ice stream geophysical and geological data indicate that during the last glacial cycle a palaeo ice stream drained the antarctic peninsula ice sheet apis through marguerite bay to the edge of the continental shelf via a bathymetric trough marguerite trough mega scale glacial lineations msgl in outer marguerite trough are formed in an acoustically transparent sediment unit consisting of a soft deformation till the association of msgl with deformation till indicates that bed deformation occurred beneath the ice stream and the thickness of the subglacial deforming layer was on the order of several metres msgl within outer marguerite trough are related to a pre existing thick sequence of soft sediments on the outer shelf and are inferred to have formed by a combination of subglacial sediment deformation by attenuation from a point source and groove ploughing morphologically the msgl differ in several respects from those documented elsewhere and this variation suggests a polygenetic origin for this subglacial landform an initial advance of the apis across the marguerite bay continental shelf at the lgm deposited a stiff subglacial till following this advance the ice margin within marguerite trough retreated 70 100 km before stabilising and depositing a grounding zone wedge an ice stream then developed in the trough and extended to the shelf edge forming a soft deformation till development of the ice stream may have been a glacio dynamic response to regional deglaciation subsequent retreat of the marguerite trough ice stream was underway by 13 490 uncorrected 14c years before present based on the geophysical and core data ice stream retreat appears to have been rapid and it contrasts with reconstructions of palaeo ice streams from other locations in antarctica this implies marked regional variations in antarctic ice stream dynamics during late quaternary deglaciation

a phenomenological paradigm for midtropospheric cyclogenesis in the indian summer monsoon abstractmidtropospheric cyclones mtcs are a distinct class of synoptic disturbances characterized by quasi stationary cyclonic circulation in midtropospheric levels which often produce heavy ra

intraseasonal periodicities in indian rainfall abstract spectral analysis of a 70 year 1901 70 record of daily precipitation from 3700 stations in the country of india is carried out to search for periodicities on subseasonal time scales during the summer monsoon two statistically significant spectral peaks are found a 40 50 day spectral peak corresponding to the madden julian oscillation is found over most of the portion of india south of 23 n the phase of the oscillation is such that the precipitation maximum appears first over the relatively dry southeastern portion of the peninsula ten to 12 days later the precipitation peaks simultaneously all along the coast west of the western ghats and along a line running across india between 20 and 25 n the precipitation maximum then spreads slowly northward and loses significance cross spectral analysis shows strong coherence between the precipitation patterns and wind oscillations the zonal wind oscillations at 850 and 200 mb am about 180 degrees out of phase equatorward of about 20 n but in pha

first observations of intraseasonal oscillations in the equatorial mesosphere and lower thermosphere we present the first evidence of strong intraseasonal 10 100 day variability of the equatorial mesosphere and lower thermosphere drawn from spectral analysis of three years of radar wind measurements of the region at christmas island 2 n 157 w oscillations in the zonal wind as large as 20 m s 1 are observed with periods 60 days at 85 95 km amplitudes attenuate near 80 km then reintensify near 75 km where they are usually of longer period and are out of phase with the upper level oscillations oscillations with periods 35 40 days are also observed at 85 95 km these oscillations are transient and usually appear when the background flow is westward similar signals are not observed in the meridional winds these facts suggest that they could be kelvin waves similar to intraseasonal variability in the equatorial lower atmosphere associated with the madden julian oscillation somewhat different time height activity at 20 days could be related to the 1 3 rossby normal mode or the 20 25 day tropospheric oscillation as it is unlikely that any of these oscillations could propagate to these heights from the lower atmosphere we postulate that they arise due to variations in gravity wave activity and transmissivity induced by intraseasonal oscillations lower down which is transferred into the mean flow when these gravity waves dissipate in the mesosphere this may mean that this intraseasonal activity is a time varying mean wind rather than a forced planetary wave

ocean drilling program leg 178 antarctic peninsula sedimentology of glacially influenced continental margin topsets and foresets abstract ocean drilling program leg 178 february april 1998 drilled two sites sites 1097 and 1103 on the outer antarctic peninsula pacific continental shelf recovered strata are no older than late miocene or early pliocene site 1097 lies on the outer shelf within marguerite trough which is a major outlet for ice expanding seaward from the antarctic peninsula and reached a maximum depth drilled of 436 6 m below the sea floor mbsf seismic stratigraphic data show flat lying upper strata resting on strata that dip gently seaward uppermost strata to a depth of 150 mbsf were poorly recovered but data suggest they consist of diamictites containing reworked and abraded marine microfauna this interval is interpreted as having been deposited largely as till produced by subglacial cannibalization of marine sediments deformation till recording ice sheet expansion across the shelf underlying gently dipping strata show massive stratified and graded diamictite facies with common bioturbation and slump stuctures that are interbedded with laminated and massive mudstones with dropstones the succession contains a well preserved in situ marine microfauna typical of open marine and proglacial marine environments the lower gently dipping succession at site 1097 is interpreted as a complex of sediment gravity flows formed of poorly sorted glacial debris site 1103 was drilled in that part of the continental margin that shows uppermost flat lying continental shelf topsets overlying steeper dipping slope foresets seaward of a structural mid shelf high drilling reached a depth of 363 mbsf with good recovery in steeply dipping continental slope foreset strata foreset strata are dominated by massive and chaotically stratified diamictites interbedded with massive and graded sandstones and mudstones the sedimentary record and seismic stratigraphy is consistent with deposition on a continental slope from debris flows and turbidity currents released from a glacial source data from sites 1097 and 1103 suggest the importance of aggradation of the antarctic peninsula continental shelf by till deposition and progradation of the slope by mass flow this may provide a model for the interpretation of palaeozoic and proterozoic glacial successions that accumulated on glacially influenced continental margins

the role of intraseasonal variability in the nature of asian monsoon precipitation abstract the structure of the mean precipitation of the south asian monsoon is spatially complex embedded in a broad precipitation maximum extending eastward from 70 e to the northwest tropical pacific ocean are strong local maxima to the west of the western ghats mountain range of india in cambodia extending into the eastern china sea and over the eastern tropical indian ocean and the bay of bengal bob where the strongest large scale global maximum in precipitation is located in general the maximum precipitation occurs over the oceans and not over the land regions distinct temporal variability also exists with time scales ranging from days to decades neither the spatial nor temporal variability of the monsoon can be explained simply as the response to the cross equatorial pressure gradient force between the continental regions of asia and the oceans of the southern hemisphere as suggested in classical descriptions of the monsoon monthly 1979 2005 and daily 1997 present rainfall estimates

intraseasonal oscillations of the monsoon circulation over south asia the space time structure of the three dimensional circulation over the south asian monsoon region has been studied using the era 40 reanalysis of the european centre for medium range weather forecasts applying multi channel singular spectrum analysis on combined daily values of horizontal winds and pressure vertical velocity at ten vertical levels for the period 1958 2001 two leading intraseasonal nonlinear oscillations were extracted the first oscillation has an average period of 50 days and propagates northeastward from the indian ocean to the indian subcontinent the second oscillation has a period of 30 days and propagates northwestward from the west pacific to the indian region both the oscillations exhibit the oscillatory and propagation features at all vertical levels from 1 000 to 100 hpa the two oscillations correspond well with similar oscillations found in outgoing longwave radiation and precipitation in earlier studies the wind oscillations also account for the active and break phases of the indian monsoon the vertical structures and propagation of specific humidity and temperature are found to be consistent with those of the winds in each oscillation the structure and movement of regional hadley and walker circulations have also been described the analyses provide further strong evidence for the existence of two distinct monsoon intraseasonal oscillations

pliocene glacial cyclicity in a deep sea sediment drift antarctic peninsula pacific margin abstract giant deep sea sediment drifts are widespread features along the continental rise of the west antarctic peninsula representing the most proximal continuous sedimentary recorders for west antarctic ice events and glacial interglacial cyclicity sediment physical geochemical records and x ray images derived from odp leg 178 site 1095 sediment drift 7 show characteristics in glacial interglacial cyclicity and associated sedimentary processes during early pliocene two boundary types dividing half cycles have been recognized 1 interglacial to glacial transitions that are distinct and characterized by a sharp boundary and abrupt change in lithology 2 glacial to interglacial transitions that are diffuse and characterized by a gradual decline of sediment physical and geochemical values with a marked reduction in sedimentation rates the boundaries defined in conjunction with magneto and biostratigraphic tie points form the framework for the calculation of relative sedimentation and accumulation rates used for reconstructing early pliocene paleoproductivity and terrigenous flux to the drift warm early pliocene climate conditions for west antarctic peninsula region are indicated by open ocean conditions in glacials short residence times of the grounded ice sheet at the shelf edge with sporadic fluctuations as well as periodic collapses of the ice sheet front we propose a 5 phase drift sedimentation model for the early pliocene and postulate a highly dynamic ice sheet likely reduced in thickness resulting in oscillations which lie closer to the shelf edge than was the case during the late quaternary

a model for neogene crustal rotations transtension and transpression in southern california two episodes of crustal rotation have occurred in the regions of southern california and the mojave desert since the beginning of miocene time an early miocene episode of clockwise crustal rotation is associated with widespread north south to north northeast south southwest crustal extension throughout southeast california and western arizona this episode is apparently related to changing subduction parameters of the farallon plate a middle miocene and later episode of clockwise rotation in the transverse ranges and bordering areas is related to shear between the pacific and north american plates in both episodes clockwise crustal rotations first occur in a deforming zone which has a component of extension across its trend and shear along its trend the effects of extension are most pronounced in the earlier episode but clear in the later one also the pacific north american deforming zone began contracting in width during pliocene time but clockwise rotations continued and are probably in progress today

late quaternary alluviation and offset along the eastern big pine fault southern california abstract determining late quaternary offset rates on specific faults within active mountain belts is not only a key component of seismic hazard analysis but sheds light on regional tectonic development over geologic timescales here we report an estimate of dip slip rate on the eastern big pine oblique reverse fault in the upper cuyama valley within the western transverse ranges of southern california and its relation to local landscape development optically stimulated luminescence osl dating of sandy beds within coarse grained alluvial deposits indicates that deposition of alluvium shed from the pine mountain massif occurred near the southern margin of the cuyama structural basin at the elevation of the cuyama river between 25 and 14 ka this alluvial deposit has been offset 10 m vertically by the eastern big pine fault providing a latest quaternary dip slip rate estimate of 0 9 m ky based on a 50 fault dip incision of the adjacent cuyama river has exposed a section of older cuyama river sediments beneath the pine mountain alluvium that accumulated between 45 and 30 ka on the down thrown footwall block of the eastern big pine fault corroborative evidence for holocene reverse slip on the eastern big pine fault is 1 m of incised bedrock that is characteristically exposed beneath 2 3 5 ka fill terraces in tributaries south of the fault the eastern big pine fault in the cuyama valley area has no confirmed record of historic rupture however based on our results we suggest the likelihood of multiple reverse slip rupture events since 14 ka

seasonal persistence and propagation of intraseasonal patterns over the indian monsoon region the space time evolution of convection over the monsoon region containing the indian subcontinent the indian ocean and the west pacific has been studied a multi channel singular spectrum analysis of the daily outgoing longwave radiation has yielded two intraseasonal oscillatory patterns and two large scale standing patterns as the most dominant modes of intraseasonal variability the oscillatory modes vary on time scales of about 45 and 28 days and their average cycles of variability are shown to correspond to the life cycles of active and break periods of monsoon rainfall over india during an active break cycle a convection dry anomaly zone first appears in the equatorial indian ocean subsequently expands to cover the indian subcontinent and finally contracts to disappear in the northern part of india some eastward and northward movements are found to be associated with both oscillatory modes while westward movement may also be associated with the 28 day mode the oscillatory modes are shown to have a large spatial scale extending to the west pacific one of the standing modes has anomalies of uniform sign covering the entire region and is related to el nino and southern oscillation enso pattern the other standing mode has a dipole structure in the equatorial indian ocean associated with large scale anomalies over india with the same sign as those over the western part of the dipole these two standing modes persist throughout the monsoon season each maintaining its respective pattern the seasonal mean monsoon is mainly determined by the two standing patterns without much contribution from the oscillatory modes the relative role of the standing patterns enso mode and dipole mode seems to be important in determining the seasonal mean during certain years

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

pliocene transpressional modification of depositional basins by convergent thrusting adjacent to the big bend of the san andreas fault an example from lockwood valley southern california 1 the big bend of the san andreas fault in the western transverse ranges of southern california is a left stepping flexure in the dextral fault system and has long been recognized as a zone of relatively high transpression compared to adjacent regions the lockwood valley region just south of the big bend underwent a profound change in early pliocene time 5 ma from basin deposition to contraction accompanied by widespread folding and thrusting this change followed the recently determined initiation of opening of the northern gulf of california and movement along the southern san andreas fault at about 6 1 ma with the concomitant formation of the big bend lockwood valley occupies a 6 km wide fault bounded structural basin in which converging blocks of paleoproterozoic and cretaceous crystalline basement and upper oligocene and lower miocene sedimentary rocks plush ranch formation were thrust over miocene and pliocene basin fill sedimentary rocks in ascending order caliente formation lockwood clay and quatal formation all the pre quatal sedimentary rocks and most of the pliocene quatal formation were deposited during a mid tertiary period of regional transtension in a crustal block that underwent little clockwise vertical axis rotation as compared to crustal blocks to the south ensuing pliocene and quaternary transpression in the big bend region began during deposition of the poorly dated quatal formation and was marked by four converging thrust systems which decreased the areal extent of the sedimentary basin and formed the present lockwood valley structural basin none of the thrusts appears presently active estimated shortening across the center of the basin was about 30 percent the formerly defined eastern big pine fault now interpreted to be two separate oppositely directed contractional reverse or thrust faults marks the northwestern structural boundary of lockwood valley the complex geometry of the lockwood valley basin is similar to other tertiary structural basins in southern california such those that underlie cuyama valley the ridge basin and the east ventura basin

ice sheet extent of the antarctic peninsula region during the last glacial maximum lgm insights from glacial geomorphology we present marine geological and geophysical data for the antarctic peninsula that call for a larger ice sheet reconstruction during the last glacial maximum lgm than suggested by previous studies such glacial reconstructions are important for quantifying post lgm sea level rise and providing boundary conditions for general circulation models megascale glacial lineations on the continental shelf surrounding antarctica provide documentation for grounded ice that was streaming swath bathymetry data nbp02 01 reveal lineations in each of the major glacial troughs except for smith trough which features grooves and bedrock drumlins 0 5 3 km spacing 1 20 elongation ratios on crystalline bedrock we place the maximum extent of ice at the seaward limit of the lineations at or near megascale glacial lineations imaged in this study and other areas surrounding antarctica including the ross sea pine island bay have a consistent morphology with elongation ratios of 80 1 and spacings of 200 600 m mode of 300 m in contrast lineations bundles canals et al 2000 in the gerlache boyd trough exhibit larger spacing 1 5 km and the upstream portions 7 km are carved directly into bedrock rather than till as suggested by previously unpublished air gun 120 hz seismic data these features have yet to be dated however they are believed to have been active during the lgm radiocarbon dates in glaciomarine sediments foraminifera and organic matter from seven glacial troughs indicate that megascale glacial lineations were formed during the lgm other geomorphic features such as the grounding zone wedge in the northwestern weddell sea formed when the ice sheet was retreating the initial retreat of the grounded ice from the outer shelf occurred by 18 500 cal yr b p the inner shelf was mostly ice free by 13 000 cal yr b p this is significantly earlier than numerical models which suggest antarctic deglaciation began at 12 000 cal yr b p this also suggests the peninsula area contributed to global sea level rise associated with meltwater pulse mwp 1a

variation of tropical cyclone activity in the south indian ocean el nino southern oscillation and madden julian oscillation effects 1 the present study examines variation of tropical cyclone tc activity in the south indian ocean sio during tc seasons december march for the period 1979 2004 the impact of the el nino southern oscillation and the madden julian oscillation mjo on the variation is revealed through a composite analysis during el nino periods tc genesis was shifted westward enhancing the formation west of 75 e and reducing it east of 75 e these changes in the genesis correspond to a westward shift of convection it may be explained by a remote effect on the sio that is the increase in sea surface temperature in the central eastern pacific alters the walker circulation and forms an anomalous anticyclonic circulation in the east sio during el nino the spatial difference in tc passages between el nino and la nina shows a significant decrease to the southeast of madagascar but a moderate increase in the central midlatitude sio indicating that tcs move farther east during el nino this change is possibly due to the anomalous southwesterlies east of madagascar variation of tc activity also depends on various mjo phases frequent tc passages for phases 2 4 strong convective activity straddles along the equatorial indian ocean versus infrequent tc passages for other phases tc tracks tend to be more south oriented in phase 3 compared with those in phases 2 and 4 this is possibly caused by the increased steering northerlies which are a part of the anticyclonic rossby wave of gill type in response to the suppressed mjo related convection in the maritime continent

principal oscillation pattern analysis of the 30 to 60 day oscillation in the tropical troposphere the principal oscillation pattern technique is used to derive an index of the 30 to 60 day oscillation in the tropical troposphere in the 200 mb equatorial velocity potential field one dominant pair of pops is found its properties compare very well with the properties of the oscillation identified in previous studies in particular a good correlation between the time evolution of the pop coefficients and area averaged outgoing long wave radiation orl is found the pops are derived from a 2 year subinterval of the whole 5 year data set this leaves independent data for subsequent verification the patterns and their characteristic numbers are almost unchanged if the whole data set is analysed also the analysis is insensitive to changes of the analysis area if the analysis is limited to 90 longitude equatorial sectors the signal is also identified and its patterns are consistent with the patterns derived from the full data set interestingly the signal is best defined in the eastern hemisphere the pops may be used to derive associated correlation patterns of other quantities in winter and summer separately the path of the oscillation has a marked annual cycle in northern winter it migrates from the indian ocean across northern australia into the region of the south pacific convergence zone spcz and in northern summer it moves from the indian ocean across south asia along the intertropical convergence zone itcz to south america the pop coefficient may be seen as a bivariate index of the state phase and strength of the 30 to 60 day oscillation since the pop technique incorporates a prediction equation for the phase of the pop coefficients the pop model allows for the prediction of the complex amplitude of the oscillation in a sequence of forecast experiments of which about two thirds used independent data the pop forecasts were found to be useful in about half of all cases for lead times of several days the correlation and rms skills were calculated for the pop forecast and for persistence the pop forecast appears to be considerably better with respect to both measures the correlation skill scores 60 after 7 days the pop forecast is most skillful in northern winter and if strong signals are present with minima of velocity potential in the eastern hemisphere

contourite drift types and their distribution in the north and south atlantic ocean basins abstract patterns of sediment accumulation under the control of deep bottom currents depend on interacting factors intensity of the regional deep circulation morphology of the sea floor coriolis effects abundance of terrigenous and biogenic supplies subsequent turbidity of deep nepheloid layers and depth of the ccd based on many examples of bottom current deposits from the atlantic and from other oceans we recognise three major types of contourite accumulation 1 giant elongate drifts 2 contourite sheets and 3 channel related drifts they generally occur in distinct topographic settings and show different geometries facies and rates of deposition in the north atlantic strong bottom circulation an open basin system and high sediment supply have led to the construction of large elongate contourite drifts which have striking relief 200 1000 m above the surrounding sea floor and are composed of muddy contourites rich in calcareous pelagic material in the south atlantic strong bottom currents are often trapped in gyre like circulation patterns around topographically closed basins or are accelerated through deep narrow connecting passages the resulting deposits are mainly extensive contourite sheets covered by fields of large sediment waves and channel related drifts including contourite fans constructed at the downstream exit of deep passages

direct constraints on antarctic peninsula ice sheet grounding events between 5 12 and 7 94 ma 1 how has the antarctic ice sheet responded to or influenced global climate change this simple question has been difficult to address because the long term records of the ice sheet s fluctuations are poorly constrained with geologic data from antarctica thus studies to date have not convincingly established how specific antarctic ice sheet events correlate with climatic eustatic or other phenomena known from low latitude and deep sea records this study focused on documenting the direct record of ice sheet advance and retreat to the antarctic peninsula s shelf edge on the peninsula s outer shelf seismic reflectors interpreted to be subglacial unconformities were correlated with published results from ocean drilling program leg 178 lithologic and chronologic control at two drill sites provided ground truth for the seismic interpretation and the timing of the antarctic peninsula ice sheet grounding events this synthesis showed that grounded ice advanced to the shelf edge on at least 12 occasions between 5 12 and 7 94 ma

ocean surface wind prediction in the north indian ocean from in situ and satellite observations using genetic algorithm 1 possibility of predicting surface wind speed in the north indian ocean from in situ observations and surface wind components from satellite scatterometer observations using an approach based on genetic algorithm ga has been demonstrated in this work the approach unlike other prediction methods provides explicit analytical forecast equation predictions made up to 3 days in advance have been found to be significantly superior to those made by persistence and autoregressive techniques

timing and extent of neogene tectonic rotation in the western transverse ranges california paleomagnetic data collected from lower miocene rocks throughout the western transverse ranges province have consistently clockwise deflected magnetic declinations which suggests that the entire province has experienced clockwise tectonic rotation during neogene time paleomagnetic declinations in lower miocene rocks increase westward from 33 5 c 11 in the san gabriel block to 91 7 7 in the western santa ynez range suggesting a westward increase in the net amount of clockwise tectonic rotation paleomagnetic data that constrain the tuning of rotation suggest that the entire western transverse ranges rotated uniformly 50 60 clockwise during the middle miocene this implies a minimum of 200 km of distributed dextral shear along the california coast and offshore during middle miocene time little tectonic rotation appears to have occurred in the western transverse ranges during late miocene time since miocene time continued clockwise rotation in the western santa ynez range 31 3 combined with counterclockwise rotation in the san gabriel block 16 has oroclinally bent the transverse ranges to the west of the san andreas fault the pliocene pleistocene clockwise rotation implies an additional 30 60 km of distributed dextral shear across the southern california coast ranges during post miocene time

exploring biological constraints on the glacial history of antarctica the evolutionary and biogeographic history of the contemporary antarctic terrestrial and marine biotas reveals many components of ancient origin for large elements of the terrestrial biota long term isolation over timescales from hundreds of thousands to tens of millions of years and thus persistence through multiple glacial cycles now appears to be the norm rather than the exception for the marine biota there are some parallels with benthic communities also including ancient components together with an incidence of species level endemism indicating long term isolation on the antarctic continental shelf although it has long been known that a few ice free terrestrial locations have existed in antarctica for up to 10 12 million years particularly in the dry valleys of victoria land along with certain nunataks and higher regions of large mountain ranges these do not provide potential refugia for the majority of terrestrial biota which occur mainly in coastal and or low lying locations and exhibit considerable biogeographic regionalisation within the continent current glacial models and reconstructions do not have the spatial resolution to detect unequivocally either the number or geographical distribution of these glacial refugia or areas of the continental shelf that have remained periodically free from ice scouring but do provide limits for their maximum spatial extent recent work on the evolution of the terrestrial biota indicates that refugia were much more widespread than has been recognised and it is now clear that terrestrial biology provides novel constraints for reconstructing the past glacial history of antarctica and new marine biological investigations of the antarctic shelf are starting to do likewise

latitudinal variation in glacial erosion rates from patagonia and the antarctic peninsula 46 s 65 s we use extensive sedimentary and marine geophysical data to derive sediment volume based millennial time scale glacial erosion rates from glacially influenced fjords and bays across a broad latitudinal transect from central patagonia 46 s to the antarctic peninsula 65 s and to determine how glacial erosion rates change with increasing latitude and decreasing atmospheric temperatures we also calculate million year time scale erosion rates for the western antarctic peninsula cordillera and inner continental shelf from seismic stratigraphic analysis of the continental margin these results are complemented by erosion rates derived from existing thermochronology data sets apatite fission track and apatite u th he for both patagonia and the antarctic peninsula regions despite considerable regional variability our results show a clear trend of decreasing with increasing latitude millennial values span two orders of magnitude from 0 02 mm yr for illiad glacier on anvers island antarctica 64 5 s to 0 83 mm yr for san rafael glacier in northern patagonia 46 5 s regional averages are three times higher for the patagonian areas than the antarctic peninsula areas this trend is interpreted to result from a general decrease in temperature and water availability at the ice bedrock interface for the antarctic peninsula study sites erosion rates are highly clustered around 0 1 mm yr with the exception of maxwell bay for which the value is 0 36 mm yr in patagonia erosion rates are more variable than in the antarctic peninsula with ranging between 0 14 mm yr europa glacier area and 0 83 mm yr san rafael glacier area this regional variability in is interpreted as due to differences in hypsometry and bedrock resistance to erosion million year time scale values derived from thermochronology ages also decrease with latitude with maximum values decreasing from 0 9 1 1 mm yr north of 46 s to 0 1 0 2 mm yr south of 48 s in patagonia and reaching 0 2 0 3 mm yr in the antarctic peninsula the sediment based million year time scale estimates for the western antarctic peninsula cordillera indicate that glacial erosion rates increased by 25 30 after 5 3 ma from 0 09 mm yr 5 3 9 5 ma to 0 11 0 12 mm yr 5 3 ma for patagonia the decrease in long term erosion rates south of 46 s is interpreted to result from relatively long periods of slow glacial erosion associated with the ice masses having been colder subpolar on the southern patagonian cordillera and having eroded at rates comparable to those we obtained for the antarctic peninsula these long term erosion rates are 1 2 orders of magnitude lower than estimates based on recent sediment yields highlighting the transient nature of high sediment flux events however our sediment volume derived millennial time scale closely approximates the maximum values of tectonic time scale values derived from thermochronology ages our combined millennial and million year time scale glacial erosion data quantify the significant decrease in rates of glacially driven denudation at geological tectonic and millennial time scales with increasing latitude from patagonia to the antarctic peninsula highlighting the influence of climate on mountain denudation

deep sea floor evidence of past ice streams off the antarctic peninsula the past existence of a giant ice stream off the northern end of the antarctic peninsula is suggested by a convex upward elongated sediment body now at a mean water depth of 1000 m because of its morphological characteristics i e a set of parallel to subparallel ridges and grooves to 100 km long with an overall width of 25 km we call this depositional body a bundle structure we hypothesize that bundle structures form by accumulation of basal deformation till under their parent ice streams from its location size and overall characteristics the bundle structure described here constitutes the best preserved largest deepest and relatively low latitude evidence of giant ice streams that flowed offshore antarctica during glacial maxima bundle structures reveal the very dynamic behavior of ice caps in the northern antarctic peninsula during the last glacial maximum with catchment areas draining rapidly under marine based critical subglacial conditions bundle structures represent a new megascale streamlined glacial landform

geomorphic indicators of active fold growth south mountain oak ridge anticline ventura basin southern california south mountain oak ridge near ventura california is an asymmetric anticlinal uplift forming at the present time above the active buried oak ridge reverse fault shortening along the oak ridge fault accumulated largely in quaternary time and is responsible for the growth and present topography of the westernmost 15 km of the ridge during the past 0 5 m y tectonic geomorphic analysis using several indices of active tectonics provides information concerning fold growth stream gradient indices are relatively high in the northern eroded fold scarp of the ridge a pattern consistent with the existence of active rapid slip on the oak ridge fault mountain front sinuosity along the northern slope of the anticlinal ridge roughly decreases from 2 to 1 toward the westernmost 10 km of observed surface folding valley floor width to valley height ratios along the northern flank of the ridge generally decrease westward from 1 5 to 0 5 values of the hypsometric integral along the northern flank increase significantly from 0 35 to 0 4 maximum 0 55 from east to west drainage density varies from 4 to 6 km km2 along both flanks of the south mountain oak ridge anticline entrenchment of streams into the southern backlimb of the fold along the westernmost 9 km of the structure decreases from 20 m to 1 m from east to west apparent backlimb rotation as measured by dip of strata along the westernmost 7 km of the fold decreases from east to west from 35 to 20 fold growth of the south mountain oak ridge anticline occurred during the past 0 5 ma following deposition of the saugus formation lateral and vertical fold growth were likely produced by westward decrease in fault slip along the buried oak ridge fault

the boreal summer intraseasonal oscillation relationship between northward and eastward movement of convection the summertime intraseasonal oscillation iso is an important component of the south asian monsoon lagged regressions of intraseasonally filtered 25 80 days outgoing longwave radiation olr reveal that centers of convection move both northward and eastward from the central equatorial indian ocean subsequent to the initiation of an iso eastward movement of convection is also seen at indian subcontinent latitudes 10 8 208n based on the regression results the summertime iso convection signal appears as a band tilting northwestward with latitude and stretching from the equator to about 208n viewed along any meridian convection appears to propagate northward while equatorial convection propagates to the east to examine the robustness of the connection between eastward and northward movement individual isos are categorized and composited relative to the strength of the large scale eastward component of convection in the central equatorial indian ocean it is found that the majority of isos that exhibit northward movement onto the indian subcontinent 42 out of 54 isos or 78 also exhibit eastward movement into the western pacific ocean it is also found that when convection in the central indian ocean is not followed within 10 20 days by convection in the western pacific ocean 12 out of 54 isos or 22 the independent northward movement of convection in the indian ocean region is somewhat stunted the link between the eastward and northward movement of convection is consistent with an interpretation of the summertime iso in terms of propagating equatorial modes the northward moving portion of convection is forced by surface frictional convergence into the low pressure center of the rossby cell that is excited by equatorial iso convection a similar convergence pattern is seen for the northern winter iso but it does not generate poleward movement due to relatively cool ssts underlying the surface convergence

large scale quaternary detachments in ventura basin southern california the ventura basin is an east north east trending trough in the california transverse ranges which records major quaternary detachment faulting at three levels the earliest thrusting occurred along weak siltstone interbeds in a sequence dominated by competent basin plain turbidite sandstone because sedimentation continued during thrusting the age rate and direction of thrusting can be worked out faulting began 1 3 m y ago and ceased 0 65 m y ago with a maximum slip rate of 2 8 mm yr to the southeast the fault set moved up a 45 ramp and ended as a blind thrust the ramp had topographic expression on the seafloor diverting turbidites around the ramp and preserving ash beds along with other hemipelagic sediments on its crest following the end of deposition 0 2 m y ago the competent basin plain turbidites underwent flexural slip folding over an incompetent miocene sequence dominated by shale underlying competent paleogene strata were not folded the south flank of the ventura avenue anticline tilted at 3 4 rad yr the anticlinal crest rose at a rate of 15 16 mm yr decelerating to 4 3 5 2 mm yr and the anticline and an adjacent syncline shortened at a rate of 20 mm yr the high rate of folding in the ventura avenue oil field resulted in overpressured sandstone reservoirs and oil water interfaces which have not had time to reach gravity equilibrium the red mountain san cayetano and santa susana faults mark the surface expression of a seismically active midcrustal detachment which produced convergence across the ventura basin at rates as high as 23 mm yr total convergence across the eastern san cayetano fault near fillmore is 11 600 2000 m in the last million years

are antarctic peninsula ice sheet grounding events manifest in sedimentary cycles on the adjacent continental rise the direct record of late miocene early pliocene antarctic peninsula ice sheet expansions from a previously published seismostratigraphic study of the outer shelf at ocean drilling program site 1097 is compared to the glacial history we deduced from published proxy evidence within coeval sections on the adjacent continental rise the proxies are sedimentary structures laminated vs massive bioturbated facies and clay minerals predominantly smectite and chlorite contents from ocean drilling program site 1095 located on the distal part of a large drift the comparison shows that more sedimentary cycles are evident on the continental rise for three of the four diatom biozones we considered this indicates that the continental rise sedimentology may indeed be related to local or regional paleoenvironmental variability including antarctic peninsula ice sheet grounding events on the adjacent outer continental shelf if correct this would be a promising result because unlike the outer continental shelf sequences drilled thus far the continental rise record is relatively continuous and can be dated using paleomagnetic and biostratigraphic data however our study also shows that no objective criteria provide direct linkages between the glacial history we deduced from the two continental rise proxies and that previously derived from the continental shelf seismic stratigraphy furthermore the two sedimentologic proxies on the continental rise do not always provide a consistent picture of glacial history when compared against each other

implications of distributed crustal deformation for exhumation in a portion of a transpressional plate boundary western transverse ranges southern california abstract spatial and temporal patterns of exhumation are inextricably linked to patterns of crustal deformation because crustal deformation drives rock uplift a new interpretation of a segment of the pacific north america transpressional plate boundary in southern california is analyzed in the context of crustal shortening rock uplift and exhumation deformation is partitioned between two structural anticlinoria formed above thrust faults that root into a mid crustal decollement the southern anticlinorium began growing after 5 ma and is characterized by almost no topographic expression rock uplift of 3 km and exhumation of

forecasting the sst space time variability of the alboran sea with genetic algorithms we propose a nonlinear ocean forecasting technique based on a combination of genetic algorithms and empirical orthogonal function eof analysis the method is used to forecast the space time variability of the sea surface temperature sst in the alboran sea the genetic algorithm finds the equations that best describe the behaviour of the different temporal amplitude functions in the eof decomposition and therefore enables global forecasting of the future time variability

quaternary flake tectonics of the california transverse ranges p residual studies suggest that the pacific american plate boundary in the upper mantle lies in the central mojave desert northeast of its crustal position at the san andreas fault focal mechanisms of some relatively deep microearthquakes suggest a flattening with depth of north dipping thrust faults resulting in a mid crustal detachment in which the central transverse ranges move south relative to the mantle this makes sense geologically if the central transverse ranges and western mojave desert are considered as tectonic flakes of brittle crystalline rocks underlain by ductile pelona schist or catalina schist which makes up the zone of decollement such ductile schists would occur today at depths comparable to those at which they were metamorphosed the detachment breaks through to the surface at the point dume malibu coast fault zone and the red mountain san cayetano santa susana sierra madre cucamonga fault zone the latter coinciding with the southern edge of the palmdale bulge the transverse ranges flake now moves west northwest relative to the western mojave flake south southwest relative to the pacific plate and northwest relative to the great valley sierra nevada the mantle boundary may rejoin the san andreas fault north of a southwest trending zone of high seismicity in the tehachapi mountains which may be produced by convergence the age of the present tectonic system may be the same as the age of the break through thrust faults these are probably no older than 2 m y and may be even younger

coarse grained terrigenous sediment deposition on continental rise drifts a record of plio pleistocene glaciation on the antarctic peninsula sediment drifts on the continental rise are located proximal to the western side of the antarctic peninsula and recorded changes in glacial volume and thermal regime over the last ca 15 m y at ocean drilling program odp site 1101 leg 178 which recovered sediments back to 3 1 ma glacial interglacial cyclicity was identified based on the biogenic component and sedimentary structures observed in x radiographs magnetic susceptibility and lithofacies descriptions glacial intervals are dominated by fine grained laminated mud and interglacial units consist of bioturbated muds enriched in biogenic components from 2 2 to 0 76 ma planktonic foraminifera and calcareous nannofossils dominate in the interglacials suggesting a shift of the antarctic polar front apf to the south near the drifts prior to 2 2 ma cyclicity cannot be identified and diatoms dominate the biogenic component and high percent opal suggests warmer conditions south of the apf and reduced sea ice over the drifts analyses of the coarse grained terrigenous fraction pebbles and coarse sand from sites 1096 and 1101 record glaciers at sea level releasing iceberg rafted debris ird throughout the last 3 1 m y analyses of quartz sand grains in ird with the scanning electron microscope sem show an abrupt change in the frequency of occurrence of microtextures at similar to 1 35 ma during the late pliocene to early pleistocene the population of quartz grains included completely weathered grains and a low frequency of crushing and abrasion suggesting that glaciers were small and did not inundate the topography debris shed from mountain peaks was transported supraglacially or englacially allowing weathered grains to pass through the glacier unmodified during glacial periods from 1 35 0 76 ma glaciers expanded in size the hid flux was very high and dropstones have diverse lithologies conditions resembling those at the last glacial maximum lgm have been episodically present on the antarctic peninsula since similar to 0 76 ma quartz sand grains show high relief fracture and abrasion common under thick ice and the ird flux is low with a more restricted range of dropstone lithologies

mechanism of the northward propagating intraseasonal oscillation insights from a zonally symmetric model abstract the propagation and initiation mechanisms of the boreal summer intraseasonal oscillation bsiso in the south asian summer monsoon are examined with a zonally symmetric atmospheric model in the axially symmetric model the effects of zonally propagating atmospheric waves are intentionally excluded the model specifies mean flows and depicts the lowest baroclinic mode and a barotropic mode in the free troposphere the two vertical modes are coupled by the time mean vertical wind shear the model atmosphere produces a 15 20 day oscillation which is characterized by northward propagation of convection from south of the equator to the indian monsoon trough region and a reinitiation of convection in the region between 10 s and the equator the northward propagation in the model is produced by the free troposphere barotropic divergence which leads convection by about a quarter of a cycle the vertical advection of summer mean easterly vertical wind shear by perturbation vertical motion inside the con

intraseasonal teleconnection between the summer eurasian wave train and the indian monsoon this study investigated the most recurrent coupled pattern of intraseasonal variability between midlatitude circulation and the indian summer monsoon ism the leading singular vector decomposition svd pattern reveals a significant coupled intraseasonal variation between a rossby wave train across the eurasian continent and the summer monsoon convection in northwestern india and pakistan hereafter referred to as nism the wave train associated with an active phase of nism rainfall displays two high pressure anomalies one located over central asia and the other over northeastern asia they are accompanied by increased rainfall over the western siberia plain and northern china and decreased rainfall over the eastern mediterranean sea and southern japan the circulation of the wave train shows a barotropic structure everywhere except the anomalous central asian high located to the northwest of india where a heat induced baroclinic circulation structure dominates the time lagged svd analysis shows that the midlatitude wave train originates from the northeastern atlantic and traverses europe to central asia the wave train enhances the upper level high pressure and reinforces the convection over the nism region meanwhile it propagates farther toward east asia along the waveguide provided by the westerly jet after an outbreak of nism convection the anomalous central asian high retreats westward composite analysis suggests a coupling between the central asian high and the convective fluctuation in the nism the significance of the midlatitude ism interaction is also revealed by the close resemblance between the individual empirical orthogonal functions and the coupled svd modes of the midlatitude circulation and the ism it is hypothesized that the eastward and southward propagation of the wave train originating from the northeastern atlantic contributes to the intraseasonal variability in the nism by changing the intensity of the monsoonal easterly vertical shear and its associated moist dynamic instability on the other hand the rainfall variations over the nism reinforce the variations of the central asian high through the monsoon desert mechanism thus reenergizing the downstream propagation of the wave train the coupling between the eurasian wave train and nism may be instrumental for understanding their interaction and can provide a way to predict the intraseasonal variations of the indian summer monsoon and east asian summer monsoon

role of north indian ocean air sea interaction in summer monsoon intraseasonal oscillation abstractair sea coupling processes over the north indian ocean associated with the indian summer monsoon intraseasonal oscillation miso are investigated observations show that miso convection an