tropospheric waveguide teleconnections and their seasonality abstractone point correlation maps of the subseasonal variability of 200 hpa meridional wind in nature and an atmospheric general circulation model are systematically analyzed to quantify the impact of the climatological mean jets on tropospheric covariability as a result of the jets acting as waveguides for the propagation of rossby waves as anticipated by linear theory signatures of jet influence are detected in terms of i the geographical position of the strongest teleconnections ii the zonal orientation and extent of prominent patterns of variability and iii the scale of the features that make up those patterns further evidence of jet waveguide influence comes from examining the seasonality of these teleconnection attributes during winter covariability can be essentially circumglobal while during summer it tends to be confined within two separate sectors of the globe where the jets are especially strong experiments with a multilevel linear planetary wave model confirm that the analyzed

patterns and processes of shell fragmentation in modern and ancient marine environments shell fragments are important components of many recent and fossil marine benthic ecosystems and can provide crucial information on past and present environmental conditions interpreting such fragments requires integrated knowledge in various fields and the information potential is therefore rarely optimally utilized this paper uses the definition of a fragment as being a piece of shell having less than 90 of its original form it then outlines the potential characteristics pathways and fates that shells and their fragments can have fragmentation is a key factor shaping the shelly part of death assemblages but it is difficult to interpret because it can be broadly caused by ecological biostratinomic or diagenetic processes and also depends on shell strength strength in turn reflects multifunctionality during ontogeny and depends on a complex set of skeletal and taphonomic factors therefore no particular shell parameter clearly determines strength but thickness microstructure type and degree of organic matrix have the strongest influence on pre and post mortality strength size measurements are usually less important for shell strength than thickness although ecologically complex size refuges from predation do exist similarly shell shape sculptural features and specific aperture types in gastropods provide various defence strategies rather than increasing strength per se key ecological factors of fragmentation include predation due to crushing peeling along with mistaken predation selfinflicted damage during predation and burrowing and more physical aspects such as impacts by stones modern studies must consider damage by benthic commercial fisheries or dredging by scientific vessels key biostratinomic factors include transportinduced abrasion littoral zone of surf washed beaches bioerosion and dissolution mainly sublittoral environments diagenetically fragmentation during compaction mainly occurs when shells are in direct contact with one another or with coarser grains taphonomic features e g drillholes have only minor influence a key step in interpreting fragments is to categorize breakage into repaired versus unrepaired diagnostic versus nondiagnostic and severe versus localized damage quantifying the above categories can then provide useful information on breakage patterns and underlying processes understanding the many characteristics of shells and their fragments is a significant interpretive tool in maximizing the information gain in palaeoecological and taphofacies analyses d 2003 elsevier science b v all rights reserved

the normality of el nino the amplitude of the el nino southern oscillation enso would be normally distributed if the coupled pacific ocean atmosphere were a linear system forced by gaussian weather noise moment estimates of skewness and kurtosis demonstrate that this is not the case for monthly mean anomalies in pacific sea surface temperatures during 1950 97 the noted predominance of el nino events compared to la nina events is related to the high skewness in the eastern pacific skewness and kurtosis both exhibit an intriguing geographical variation from positive in the eastern to negative in the western pacific we have also examined nino 3 indices generated by three climate models having widely different complexity these exhibit a wide range of skewness and kurtosis values rather different from those found for the observations skewness and kurtosis can be used to diagnose non linear processes and provide powerful tools for validating models and for testing observed sea surface temperatures for the presence of possible climate change

unstable relationship between the pacific decadal oscillation and eastern china summer precipitation insights from the medieval climate anomaly and little ice age the eastern china summer precipitation is related to the pacific decadal oscillation pdo on interdecadal time scales in modern times but it remains unclear whether such a relationship holds prio

a north pacific short wave train during the extreme phases of enso abstract sea surface temperatures ssts exhibit an interannual seesaw between the eastern and western tropical pacific in concert with the el nino southern oscillation enso cycle evidence accumulated from previous studies suggests that a teleconnection link may exist between enhanced rainfall convection in the western pacific and precipitation severe weather over north america the aforementioned link could possibly be established by a teleconnection wave pattern induced by the anomalously warm cold sst anomalies in the western tropical pacific to demonstrate this possibility a fourier scale separation was introduced to divide the enso anomalous circulation into two wave regimes long wave waves 1 3 and short wave waves 4 15 the classic pacific north american teleconnection pattern is formed by the long wave regime in contrast emerging in the short wave regime is a well organized wave train that propagates from the western subtropical pacific along the north pacific rim into north america in

a pathway connecting the monsoonal heating to the rapid arctic ice melt abstractthis study provides a monsoonal link to the rapid arctic ice melt each year the planetary scale african asian monsoonal outflow near the tropopause carries a large anticyclonic gyre that has a longitudinal spread that occupies nearly half of the entire tropics in recent years the south asian summer monsoon has experienced increased rainfall over northwestern india and pakistan and it has also contributed to more intense local anticyclonic outflows from this region the western lobes of these intense upper high pressure areas carry outflows with large heat fluxes from the monsoon belt toward central asia and eventually to the region of the rapid ice melt of the canadian arctic in this study this spectacular pathway has been defined from airflow trajectories heat content and heat flux anomalies most of these show slow increasing trends in the last 20 years the monsoonal connection to the rapid arctic ice melt is a new contribution of this study this is shown from the passage of a vertical c

modelling the influence of north atlantic multidecadal warmth on the indian summer rainfall 1 ensemble experiments with an atmospheric general circulation model reveal that a positive warm ocean phase of the atlantic multidecadal oscillation amo increases indian summer rainfall the intensification is driven by extratropical north atlantic warmth with some cancellation associated with monsoon weakening in response to tropical north atlantic warmth mechanistically warm extratropical north atlantic ssts increase local rainfall inducing an arching extratropical wavetrain response the latter leads to intensified northern subsidence of monsoon mean meridional streamflow as well as widespread low surface pressure over north africa the middle east and the western indian ocean contributing to a strengthened indian monsoon trough and increased monsoon rainfall warm tropical north atlantic ssts primarily increase local tropical atlantic rainfall that induces a tropically confined response consisting of low level easterly wind anomalies over the indian ocean and dynamically induced subsident drying over india

southern hemisphere circulation features associated with el nino southern oscillation events abstract composite seasonal mean and anomaly fields prepared from operational numerical analyses have been used to describe the southern hemisphere sh circulation features associated with el nino southern oscillation enso events the period of analyses available 1972 83 has limited the composites to include only three enso events the reliability and stability of the composites has been tested using multiple permutation methods and by comparison with the results obtained using a longer period 1950 79 of sh rawinsonde station data in the sh winter a weak equivalent barotropic wavetrain pattern of anomalies extends over australia and the south pacific ocean to south america this wavetrain pattern is quite variable in amplitude and location between enso events although it is more stable over the subtropical pacific in the sh summer the circulation anomalies are more zonally symmetric with increased height at low and high latitudes and decreased height in middle latitudes the circulation anoma

cross seasonal influence of the december february southern hemisphere annular mode on march may meridional circulation and precipitation abstractnew evidence suggests that interannual variability in zonal mean meridional circulation and precipitation can be partially attributed to the southern hemisphere annular mode sam the dominant mode of climate variability in the southern hemisphere sh extratropics a cross seasonal correlation exists between the december february djf sam and march may mam zonal mean meridional circulation and precipitation this correlation is not confined to the sh it also extends to the northern hemisphere nh subtropics when the preceding djf sam is positive counterclockwise and clockwise meridional cells accompanied by less and more precipitation occur alternately between the sh middle latitudes and nh subtropics in mam in particular less precipitation occurs in the sh middle latitudes the sh tropics and the nh subtropics but more precipitation occurs in the sh subtropics and the nh tropics a framework is built to explain the cross seasonal impact of sam related sst anomalies evidence indic

the british baikal corridor a teleconnection pattern along the summertime polar front jet over eurasia abstractthe british baikal corridor bbc pattern a new teleconnection along the summertime upper tropospheric polar front jet pfj is investigated based on observational and reanalysis datasets

circumglobal teleconnections the jet stream waveguide and the north atlantic oscillation abstract monthly and seasonally averaged upper tropospheric northern hemisphere winter fields are examined to determine whether the waveguiding effect of the time averaged tropospheric jets on low frequency disturbances that is predicted by theory does affect the behavior of these disturbances it is found that indeed disturbances in the vicinity of the mean jets particularly the jet that stretches across south asia are fundamentally different from those that reside in regions where the mean winds have weaker meridional gradients like the mid pacific patterns of variability in the jets tend to be smaller scale and to consist of zonally oriented chains of anomalies while variability in the mid pacific is composed of patterns with distinct meridional orientation because they are meridionally trapped and zonally elongated patterns associated with the jet stream waveguide connect activity at points that are much farther apart than do patterns in other regions of the globe within the south asian waveg

role of equatorial central pacific and northwest of north atlantic 2 metre surface temperatures in modulating indian summer monsoon variability the interannual variability of indian summer monsoon rainfall ismr have been examined in association with the variability of 2 metre surface temperature 2mst and lower and upper tropospheric pressure and wind patterns over the globe using era 40 reanalysis dataset the analysis of 44 years 1958 2001 data reveals a recurrent negative phase of enso la nina pattern the increase in 2mst over tropical southwest pacific and intensification of subtropical westerly jet stream over indian ocean due to the consequence of thermal wind balance the intensification of jet forms anticyclonic anomaly which intensifies mascarene high as the atmospheric response is equivalent barotropic over there the mascarene high intensifies the cross equatorial flow and hence indian summer monsoon ism circulation while during non enso years data reveals a recurrent positive relationship of ismr with 2mst anomaly over northwest of north atlantic and intensification and shift of north atlantic westerly jet stream to higher latitudes the jet stream intensifies the meridional vorticity dipole formed due to azores high and the entrance of asian subtropical westerly jet stream over north atlantic and west mediterranean sea a wave activity flux for stationary rossby waves diverges out of the vorticity dipole toward downstream along the asian jet stream over the eurasian region the jet stream acts as a wave guide and the successive troughs and ridges of the rossby waves travel along the jet and influence upper tropospheric tibetan high and hence ism circulation

new example of devonian predatory boreholes and the influence of brachiopod spines on predator success three abundant devonian frasnian brachiopod species from the lime creek fm of iowa usa douvillina arcuata devonoproductus walcotti and pseudoatrypa devoniana contain boreholes pooled drilling frequency is 10 6 the boreholes are small usually 1 0 mm diameter cylindrical and drilled perpendicular to the shell surface the borings appear to be type a boreholes as described by ausich and gurrola 1979 j paleontol 53 335 344 based on multiple criteria including statistically significant stereotypy with respect to valve preference site on valve and size class of the prey the boreholes are inferred to be predatory or parasitic in origin for each species the predator preferred to attack the valve closest to the substrate regardless of whether that was the pedicle or brachial valve boreholes were concentrated over the muscle field on each of the three species the success percentage percent of complete holes was statistically lower 2 p 0 04 for the spinose devonoproductus walcotti 33 33 than for the non spinose but otherwise morphologically similar douvillina arcuata 54 22 in spite of the fact that d walcotti has a thinner shell this is the first quantitative evidence for an anti predatory function for brachiopod spines

impacts of the pacific japan and circumglobal teleconnection patterns on the interdecadal variability of the east asian summer monsoon abstractbased on the twentieth century reanalysis 20cr dataset the dominant modes of interdecadal variability of the east asian summer monsoon easm are investigated through a multivariate empirical orthogonal function analysis mv eof the first mode ea1 is characterized by an anomalous cyclone centered over taiwan and an anomalous anticyclone centered over the bohai sea these phenomena are part of the meridional wave like teleconnection pattern propagating poleward from the southern tropical western north pacific wnp referred to as the interdecadal pacific japan pj pattern the interdecadal pj pattern is driven by negative anomalous convective heating over the southern tropical wnp which is associated with the interdecadal pacific oscillation ipo and the interdecadal indian ocean basin mode iobm the amplitude of the ea1 and its contribution to the total variance of the easm decrease remarkably after the 1960s the second mv eof mode ea2 is characterized by cyclone anomalies extendin

patterns of drilling predation in relation to stratigraphy locality and sieve size insights from the eocene molluscan fauna of the paris basin abstract predatory drilling traces are routinely used to evaluate temporal patterns in animal behaviour however for testing such trends it is important to consider natural and methodological variability that may play a role in shaping drilling patterns the present study attempts to test this notion by evaluating the drilling patterns of the molluscan fauna in relation to stratigraphy locality sieve size 4 mm 2 mm 1 mm and taxonomic affinity at class level we studied drilling predation using molluscan specimens from three localities grignon la ferme de l orme fleury la riviere representing a variety of elementary depositional sequences eds from the middle lutetian strata of the paris basin the overall drilling frequency df averaged over the three localities is 17 bivalves show a significantly higher overall df 18 compared to gastropods 14 and scaphopods species composition and diversity has been used previously to resolve the debate on climate conditions of the eocene paris basin through a comparison to modern analogues we have used a similar approach by comparing predation patterns with recent localities of subtropical and temperate regions the available data from the eocene paris basin from the warm temperate northern adriatic sea and from the sub tropical red sea show very heterogeneous patterns depending on the drilling metric considered considering the strong patchiness of drilling predation within each of these basins and reported from many other studies we conclude that a climatic affiliation of the eocene paris basin based on drilling metrics is not yet possible

physical processes involved in the 1988 drought and 1993 floods in north america abstract an analysis of the spring summer 1988 drought and 1993 floods over north america reveals a reversal in the sign of anomalies in several fields large sea surface temperature anomalies of opposite signs existed in the tropical pacific with strong la nina conditions in 1988 and a mature el nino in 1993 the distribution of tropical convection in the convergence zones and associated latent heating of the atmosphere were correspondingly altered implying a large scale switch in the anomalous tropical heating and forcing of extratropical quasi stationary waves in the atmosphere influencing the subtropical jet stream over the north pacific and across north america in 1988 the jet stream and the closely related storm track of high frequency disturbances in the upper troposphere were displaced into canada well north of the normal location the farthest north of any year from 1979 to 1993 in 1993 a broader jet stream and the storm track were displaced well south of normal to a more springlike location a

teleconnections in the geopotential height field during the northern hemisphere winter abstract contemporaneous correlations between geopotential heights on a given pressure surface at widely separated points on earth referred to as teleconnections in this paper are studied in an attempt to identify and document recurrent spatial patterns which might be indicative of standing oscillations in the planetary waves during the northern hemisphere winter with time scales on the order of a month or longer a review of existing literature on the subject reveals the existence of at least four such patterns the north atlantic and north pacific oscillations identified by walker and bliss 1932 a zonally symmetric seesaw between sea level pressures in polar and temperature latitudes first noted by lorenz 1951 and what we will refer to as the pacific north american pattern which has been known to operational long range forecasters in this country since the 1950 s a data set consisting of nmc monthly mean sea level pressure and 500 mb height analyses for a 15 year period is used as a basis fo

basin mode of indian ocean sea surface temperature and northern hemisphere circumglobal teleconnection 1 observational analysis and model experiments show that the sea surface temperature anomaly associated with the indian ocean basin mode iobm which persists from spring to summer can generate significant circumglobal teleconnection cgt in the northern hemisphere summer midlatitude atmosphere a warm iobm can induce a new atmospheric heating source in the south asia through a positive feedback an enhanced indian summer monsoon through the increased precipitation in the south asia induces an atmospheric heating source there this new atmospheric heating source generates an anomalous high to its northwest over the western central asia which in turn generates an eastward downstream atmospheric wave train forming the cgt

classification seasonality and persistence of low frequency atmospheric circulation patterns abstract orthogonally rotated principle component analysis rpca of northern hemisphere 1 month mean 700 mb heights is used to identify and describe the seasonality and persistence of the major modes of interannual variability the analysis is detailed and comprehensive in that 1 a high resolution approximately equal area 358 point grid is used for the virtually maximum possible 35 year period of record 2 a positive bias in the nmc data base in the early 1950s in the subtropics is largely eliminated for the first time and 3 homogeneous separate analyses of each month of the year are carried out detailing the mouth to month changes in the dominant circulation patterns winter results are similar to those of other recent rpca and teleconnection studies except that some less obvious patterns are identified and further detail of the better known patterns is provided two north south dipole patterns are found over the pacific ocean west pacific oscillation and east pacific pattern and over the atla

on the dynamics of austral heat waves this work examines summer heat wave events in four different regions of australia southwest central southeast and northeast to assess similarities and differences in the circulations that precede accompany and follow the heat wave events a series of circulation composites are constructed for days from 10 days prior to 5 days following onset of each heat wave event the composites of geopotential height anomalies and wave activity flux vectors show that heat waves in southwest and southeast australia are preceded by coherent wave train structures in the indian ocean region accompanied by blocking in the australian region as an amplified node of the wave train structure and followed by coherent responses of wave train patterns in the pacific and south america regions the heat wave blocking high is maintained by convergence of wave activity in a well defined wave channel the concentration of wave activity in the block is aided by the formation of a subtropical jet branch and wave barrier on the equatorward side of the block heat waves in central and northeast australia show similar wave train life cycle responses but with a proximate ridge in the midtroposphere and a trough in the nearby waveguide region heat waves in australia can be viewed as an element of successive expression of the planetary waveguide modes in the southern hemisphere and serve as signifiers of organized active phases of these modes

validation of taxon specific sampling by novice collectors for studying drilling predation in fossil bivalves abstract although bulk sampling has been considered to provide more robust information on predation in the fossil record than taxon specific targeted sampling previous work suggested that targeted sampling even by a trained novice can yield results comparable to bulk sampling the present study further investigates potential bias introduced by collectors with different experience levels by comparing drilling predation metrics for samples made by five novice and three veteran collectors we demonstrate that trained novices produce results comparable to those of experienced collectors and that results of targeted sampling are comparable to bulk sampling targeted sampling was performed in the lower waccamaw formation lower pleistocene at register quarry near old dock nc five replicate taxon specific samples were obtained by each collector for the bivalves astarte concentrica cyclocardia granulata and lirophora latilirata shell length and thickness were measured and position and size of drillholes were determined frequency of left valves drilling frequency prey effectiveness and size selectivity were determined for each taxon replicate for each variable the results for the novice collectors were compared to those from bulk samples and all veteran collectors nearly all significant differences in the unstandardized data occurred in the size related variables length and thickness when data were size standardized as in many other drilling predation studies only 3 3 of 174 tests for statistical differences in collection methods were significant and none of the 157 tests for differences in novice and veteran sampling was significant previous results were not anomalous use of targeted sampling in studying drilling predation is again validated and collector expertise is shown to have minimal impact

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

interannual variability of the asian subtropical westerly jet in boreal summer and associated with circulation and sst anomalies the interannual variability of the asian subtropical westerly jet aswj in boreal summer is investigated through the diagnosis of 54 year 1960 2013 ncep ncar reanalysis data the main characteristics of two leading empirical orthogonal function patterns of 200 hpa zonal wind anomalies are the meridional displacement and southwest northeast tilting of aswj the first leading mode has significant periods of 4 9 years whereas the second mode has significant periods of 3 6 and 7 7 years respectively the two modes exhibit an equivalent barotropic structure and are associated with a distinctive north south and east west dipole rainfall pattern in china respectively the positive phase of the first leading mode appears during el nino developing phase whereas the positive phase of the second mode occurs during la nina decaying phase a mechanism is put forth based on observational analysis and agcm sensitivity experiments the positive phase of the first mode is primarily driven by the combined effect of a cold sst anomaly ssta in mid latitude north pacific and a warm ssta in tropical indian ocean and pacific in response to the ssta forcing a zonally oriented north south tropospheric temperature dipole is induced while the tropospheric warming in the tropics arises from el nino like heating the tropospheric cooling in the mid latitudes arises possibly from the local ssta forcing for the positive phase of the second mode the upper tropospheric anticyclonic vorticity anomaly in the east pole arises from local ssta forcing in north pacific whereas the cyclonic anomaly in the west pole results from southeastward rossby wave energy emanation from north atlantic to east asia

interdecadal variations of the silk road pattern abstractbased on several reanalysis and observational datasets this study suggests that the silk road pattern srp a major teleconnection pattern stretching across eurasia in the boreal summer shows clear interdecadal variations that explain approximately 50 of its total variance the interdecadal srp features a strong barotropic wave train along the asian subtropical jet resembling its interannual counterpart additionally it features a second weak wave train over the northern part of eurasia leading to larger meridional scale than its interannual counterpart the interdecadal srp contributes approximately 40 of the summer surface air temperature s variance with little uncertainty and 10 20 of the summer precipitation s variance with greater uncertainty over large domains of eurasia the interdecadal srp shows two regime shifts in 1972 and 1997 the latter shift explains over 40 of the observed rainfall reduction over northeastern asia and over 40 of the observed warming over eastern europe

metastability of northern hemisphere teleconnection modes abstractthis study applies a finite element bounded variation vector autoregressive method to assess midtropospheric flow regimes characterized by regime switches between metastable states the flow is assessed in reanalysis data from three different reanalysis sets assimilating surface data only surface and upper air data and ocean surface and upper air data results are generally consistent across the reanalyses and confirm the utility of surface only reanalyses for capturing midtropospheric variability the method is applied to a set of regional domains in the northern hemisphere and for the full hemispheric domain composites of the metastable states for each region yield structures that are consistent with the well documented teleconnection modes the north atlantic oscillation in the atlantic ocean the pacific north america pattern pna in the pacific ocean and scandinavian blocking over eurasia the pna mode includes a clear waveguide structure in midlatitudes the northern hemisphere doma

the formation mechanism of the bonin high in august the bonin high is a subtropical anticyclone that is predominant near japan in the summer this anticyclone is associated with an equivalent barotropic structure often extending throughout the entire troposphere although the equivalent barotropic structure of the bonin high has been known for years among synopticians because of its importance to the summer climate in east asia there are few dynamical explanations for such a structure the present paper attempts to provide a formation mechanism for the deep ridge near japan we propose a new hypothesis that this equivalent barotropic ridge near japan is formed as a result of the propagation of stationary rossby waves along the asian jet in the upper troposphere the silk road pattern first the monthly mean climatology is examined in order to demonstrate this hypothesis it is shown that the enhanced asian jet in august is favourable for the propagation of stationary rossby waves and that the regions of descent over the eastern mediterranean sea and the aral sea act as two major wave sources second a primitive equation model is used to simulate the climatology of august the model successfully simulates the bonin high with an equivalent barotropic structure the upper tropospheric ridge is found to be enhanced by a height anomaly of more than 80 m at 200 hpa when a wave packet arrives sensitivity experiments are conducted to show that the removal of the diabatic cooling over the asian jet suppresses the silk road pattern and formation of an equivalent barotropic ridge near japan while the removal of the diabatic heating in the western pacific does not copyright 2003 royal meteorological society

understanding the interdecadal variability of east asian summer monsoon precipitation joint influence of three oceanic signals abstracteast asian summer monsoon precipitation easmp features complicated interdecadal variability with multiple time periods and spatial patterns using century long datasets of hadisst cru precipitation and era 20c reanalysis this study examines the joint influence of three oceanic interdecadal signals i e pacific decadal oscillation pdo atlantic multidecadal oscillation amo and indian ocean basin mode iobm on the easmp which however is found not to be simply a linear combination of their individual effects when pdo and amo are out of phase the same sign sst anomalies occur in north pacific and north atlantic and a zonally orientated teleconnection wave train appears across the eurasian mid high latitudes propagating from north atlantic to northern east asia along the asian westerly jet waveguide correspondingly the interdecadal precipitation anomalies are characterized by a meridional tripole mode over eastern china when pdo and amo are in phase with opposite sign sst anomal

tropical extratropical teleconnections in boreal summer observed interannual variability abstractmaximum covariance analysis is performed on the fields of boreal summer tropical rainfall and northern hemisphere nh 200 hpa height for the 62 yr period of record of 1948 2009 the leading mode which appears preferentially in summers preceding the peak phases of the el nino southern oscillation enso cycle involves a circumglobal teleconnection cgt pattern in the nh extratropical 200 hpa height field observed in association with indian monsoon rainfall anomalies the second mode which tends to occur in summers following enso peak phases involves a western pacific north america wpna teleconnection pattern in the height field observed in association with western north pacific summer monsoon rainfall anomalies the cgt pattern is primarily a zonally oriented wave train along the westerly waveguide while the wpna pattern is a wave train emanating from the western pacific monsoon trough and following a great circle the cgt is accompanied by a pronounced tropical extratropical seesaw in t

westerlies asia and monsoonal asia spatiotemporal differences in climate change and possible mechanisms on decadal to sub orbital timescales abstract the westerlies dominated climatic regime wdcr in the present interglacial period was proposed because precipitation moisture variations between arid central asia and mid latitude monsoonal asia are out of phase or anti phased on different timescales during the holocene in this study we first review the development of the theoretical framework of the wdcr and then outline the boundary of its core area from the caspian sea in the west to the western hexi corridor in the east with the northern and southern limits coinciding with the domain of arid central asia next we present a synthesis of multiple lines of evidence for the occurrence of the wdcr on multi millennial sub orbital herein to decadal timescales during the holocene finally we examine the possible physical mechanisms responsible for the wdcr we find that external factors insolation changes induced by orbital factors generated the wdcr on a sub orbital timescale whereas a circum global teleconnection silk road pattern was the most significant factor responsible for the wdcr on centennial and decadal timescales the study provides a comprehensive summary of the development of our knowledge of the wdcr over the past several decades together with a tentative theoretical framework for understanding climatic and environmental changes within its region of influence in addition it forms a scientific basis for environmental management and ecological restoration in this arid region in the context of global warming

circumglobal teleconnection in the northern hemisphere summer analysis of the 56 yr ncep ncar reanalysis data reveals a recurrent circumglobal teleconnection cgt pattern in the summertime midlatitude circulation of the northern hemisphere this pattern represents the second leading empirical orthogonal function of interannual variability of the uppertropospheric circulation the cgt having a zonal wavenumber 5 structure is primarily positioned within a waveguide that is associated with the westerly jet stream the spatial phases of cgt tend to lock to preferred longitudes the geographically phase locked patterns bear close similarity during june august and september but the pattern in july shows shorter wavelengths in the north pacific north america sector the cgt is accompanied by significant rainfall and surface air temperature anomalies in the continental regions of western europe european russia india east asia and north america this implies that the cgt may be a source of climate variability and predictability in the above mentioned midlatitude regions the cgt has significant correlations with the indian summer monsoon ism and el nino southern oscillation enso however in normal ism years the cgt enso correlation disappears on the other hand in the absence of el nino or la nina the cgt ism correlation remains significant it is suggested that the ism acts as a conductor connecting the cgt and enso when the interaction between the ism and enso is active enso may influence northern china via the ism and the cgt additionally the variability of the cgt has no significant association with the arctic oscillation and the variability of the western north pacific summer monsoon the circulation of the wave train shows a barotropic structure everywhere except the cell located to the northwest of india where a baroclinic circulation structure dominates two possible scenarios are proposed the abnormal ism may excite an anomalous west central asian high and downstream rossby wave train extending to the north pacific and north america on the other hand a wave train that is excited in the jet exit region of the north atlantic may affect the westcentral asian high and thus the intensity of the ism it is hypothesized that the interaction between the global wave train and the ism heat source may be instrumental in maintaining the boreal summer cgt

pacific east asian teleconnection how does enso affect east asian climate observational evidence is presented to show a teleconnection between the central pacific and east asia during the extreme phases of enso cycles this pacific east asian teleconnection is confined to the lower troposphere the key system that bridges the warm cold events in the eastern pacific and the weak strong east asian winter monsoons is an anomalous lower tropospheric anticyclone cyclone located in the western north pacific the western north pacific wind anomalies develop rapidly in late fall of the year when a strong warm or cold event matures the anomalies persist until the following spring or early summer causing anomalously wet dry conditions along the east asian polar front stretching from southern china northeastward to the east of japan kuroshio extension using atmospheric general circulation and intermediate models the authors show that the anomalous philippine sea anticyclone results from a rossby wave response to suppressed convective heating which is induced by both the in situ ocean surface cooling and the subsidence forced remotely by the central pacific warming the development of the anticyclone is nearly concurrent with the enhancement of the local sea surface cooling both the anticyclone and the cooling region propagate slowly eastward the development and persistence of the teleconnection is primarily attributed to a positive thermodynamic feedback between the anticyclone and the sea surface cooling in the presence of mean northeasterly trades the rapid establishment of the philippine sea wind and sst anomalies implies the occurrence of extratropical tropical interactions through cold surge induced exchanges of surface buoyancy flux the central pacific warming plays an essential role in the development of the western pacific cooling and the wind anomalies by setting up a favorable environment for the anticyclone sst interaction and midlatitude tropical interaction in the western north pacific

a fossil record full of holes the phanerozoic history of drilling predation the evolutionary history of drilling predation despite a long and rich fossil record precambrian holocene contains a 120 m y gap late triassic early cretaceous drilled bivalve and brachiopod shells from jurassic deposits of hungary india and four localities documented in the literature indicate that drillers may have existed continuously throughout the mesozoic they may have been descendants of paleozoic predators unknown mesozoic carnivores or precursors of modern drillers a literature database suggests three major phases in the phanerozoic history of drilling predators 1 the paleozoic phase latest precambrian carboniferous dominated by rare to moderately frequent drillings in brachiopods and sessile echinoderms 2 the mesozoic phase permian early cretaceous with very rare or even facultative drillers that had little impact on marine benthic communities but nevertheless may have been present continuously and 3 the cenozoic phase late cretaceous holocene dominated by frequent gastropod drillings in mollusks

the signature of enso in global temperature and precipitation fields derived from the microwave sounding unit abstract global temperature anomalies associated with enso are investigated making use of a 13 year record of gridded temperature and precipitation data from the microwave sounding unit msu the warm phase of the enso cycle during this period was characterized by an overall warming of the tropical troposphere superimposed upon a distinctive equatorially symmetric dumbbell shaped pattern straddling the equator near 140 w accompanied by negative anomalies along the equator over the western pacific by means of singular value decomposition svd analysis it is shown that this pattern fluctuated in phase with the displacements of convective activity over the equatorial pacific as reflected in the anomalies in outgoing longwave radiation olr and msu precipitation fields fluctuations in mean tropical tropospheric temperature lagged the olr anomalies and the related temperature pattern by about 3 months the same dumbbell shaped pattern was evident with reversed polarity in the lower stratosphere tog

influences of enso induced indo western pacific sst anomalies on extratropical atmospheric variability during the boreal summer the causes for the observed occurrence of anomalous zonally symmetric upper level pressure ridges in the midlatitude belts of both hemispheres during the year after warm el nino southern oscillation enso events have been investigated sea surface temperature sst anomalies in the indo western pacific iwp sector were simulated by allowing an oceanic mixed layer model for that region to interact with local atmospheric changes forced remotely by observed enso episodes in the eastern central tropical pacific the spatiotemporal evolution of these sst conditions through a composite enso cycle was then inserted as lower boundary conditions within the iwp domain in an ensemble of atmospheric general circulation model gcm integrations this experimental setup is seen to reproduce zonally symmetric geopotential height anomalies with maximum amplitudes being attained over the extratropics in the boreal summer after the peak phase of enso the model evidence hence supports the notion that these globalscale atmospheric changes are primarily responses to sst perturbations in iwp which are in turn linked to enso variability in the equatorial pacific by the atmospheric bridge mechanism experimentation with a stationary wave model indicates that the eastern hemisphere portion of the aforementioned atmospheric signals are attributable to forcing by tropical heat sources and sinks associated with precipitation anomalies in the iwp region which are closely related to the underlying sst changes diagnosis of the output from the gcm integrations reveals that these circulation changes due to diabatic heating are accompanied by alterations of the propagation path and intensity of the high frequency eddies at locations farther downstream the geopotential tendencies associated with the latter disturbances bear some resemblance to the anomalous height pattern in the western hemisphere such local eddy mean flow feedbacks hence contribute to the zonal symmetry of the atmospheric response pattern to forcing in the iwp region analysis of zonally averaged circulation statistics indicates that the mean meridional circulation induced by divergence of anomalous transient eddy momentum fluxes in enso events could also generate zonally symmetric perturbations in midlatitudes the model simulated precipitation and surface temperature anomalies in the north american sector in response to sst changes in iwp suggest an increased frequency of droughts and heat waves in that region during the summer season after warm enso events

intraseasonal variations of the british baikal corridor pattern abstractthe british baikal corridor bbc pattern is the dominant waveguide mode trapped along the summertime polar front jet over northern eurasia it consists of four geographically fixed centers

barotropic wave propagation and instability and atmospheric teleconnection patterns abstract a global barotropic model linearized about the 300 mb climatological mean january flow is perturbed by applying a series of localized forcings distributed throughout the tropics and subtropics structures which resemble the observed pacific north american and east atlantic teleconnection patterns noted by wallace and gutzler 1981 tend to recur in the responses similar patterns are found to result from the dispersion of isolated initial perturbations placed at a variety of locations in the tropics and midlatitudes it is shown that these structures are related to the most rapidly growing mode associated with barotropic instability of the zonally varying climatological basic state in the absence of damping this mode has an e folding time of about a week and a period close to 50 days in localized regions the instantaneous growth rates can be competitive with those of baroclinic instability these episodes of rapid local barotropic growth are interspersed with intervals in which the local

global extratropical response to diabatic heating variability of the asian summer monsoon abstract global teleconnections associated with the asian summer monsoon convective activities are investigated based on monthly data of 29 northern hemisphere summers defined as june september jjas two distinct teleconnection patterns are identified that are associated respectively with variabilities of the indian summer monsoon and the western north pacific summer monsoon the indian summer monsoon convective activity is associated with a global pattern that has a far reaching connection in both hemispheres whereas the western north pacific summer monsoon convective activity is connected to a southern hemisphere wave train that influences the high latitude south pacific and south america a global primitive equation model is utilized to assess the cause of the global circulation anomalies the model responses to anomalous heatings of both monsoon systems match the general features of the observed circulation anomalies well and they are mainly controlled by linear processes the response patterns ar

dynamics of atmospheric teleconnections during the northern summer abstract in this paper the mechanisms of northern summertime teleconnections are investigated using a barotropic model in a series of numerical experiments we study the atmospheric response over the eastern pacific north america to an idealized local divergence source corresponding to the northward displacement of the itcz in the eastern pacific it is found that the response is much stronger in june than in may and is strongest when the forcing is located north of about 10 n this can be explained in terms of the refractive properties of the climatoloigical summertime subtropical jet stream over north america in another series of experiments we examine the global response as a function of the longitudinal location of the tropical forcing a wave train emanating from the subtropics of the western pacific near the philippines arching across the aleutians and the gulf of alaska and terminating with a high anomaly over the continental united states appears over a wide longitudinal range of local forcing

the midlatitude warming during 1998 2000 large scale tropospheric warming of the northern and southern hemisphere extratropics occurred during the period january 1998 january 2000 the anomalies were remarkable for their amplitude their persistence their zonal symmetry with warming occurring at all longitudes between 30 50 degrees latitude and their axial symmetry with respect to the equator the origin of the anomalies are investigated using atmospheric general circulation models forced by the global sea surface temperatures ssts of this period two ensembles based on different models reproduce the key observed features indicating that the unusual climate state was forced by the global ssts however the atmospheric states were unrelated to the strong and protracted la nina of the east equatorial pacific ocean during this time we speculate on the role of the indo pacific warm pool which itself experienced unprecedented warming in 1998 and 1999

horizontal energy propagation in a barotropic atmosphere with meridional and zonal structure abstract to investigate how the propagation of energy away from steady sources may be influenced by the horizontal structure of the time averaged flow in the troposphere solutions to a barotropic model are displayed and interpreted the model is steady and linearized about a basic state which varies in latitude and longitude emphasis is placed on cases where the longitudinal variations are gradual many of the results can be analyzed by locally applying tools developed for zonally symmetric basic states e g ray tracing and refractive indices simple background flows are constructed which have longitudinally confined critical lines reflective surfaces wave guides and regions conducive to propagation an example is given in which longitudinal derivatives of the basic state are significant the theory of ray tracing in a two dimensional wind must be employed as an interpretive tool in this case it is concluded that zonal variations tend to enhance poleward equatorward propagation in large scale tr

oceanic forcings of the interdecadal variability in east asian summer rainfall abstractin this study it was found that the pacific decadal oscillation pdo and the atlantic multidecadal oscillation amo are shown to be the two major drivers of the interdecadal variability of summer rainfall over east asia the first leading mode pc1 of this interdecadal variability associated with an in phase variation of rainfall anomalies along the yangtze river valley and huanghe huaihe river valley in china is attributed to the pdo while the second leading mode pc2 associated with seesawlike rainfall anomalies between the yangtze river valley and huanghe huaihe river valley is attributed to the amo the amo teleconnects its influence to the east asian region and beyond through a circumglobal stationary baroclinic wave train extending from the atlantic ocean through the eurasian continent and extending to north america the amo also altered the nature of the pdo through this atmospheric teleconnection resulting in the occurrence of a different pdo pattern pseudo pdo between the 1

fluctuations in northern hemisphere 700 mb height field associated with the southern oscillation abstract variations in the mid troposphere circulation associated with the southern oscillation so are investigated and documented using mean monthly 700 mb height data for the period 1951 79 the so was defined by a southern oscillation index soi consisting of the difference in normalized mean monthly sea level pressures at tahiti and darwin results for all four seasons are presented in the form of lagged as well as contemporaneous correlations and composites of height anomalies obtained separately for high and low soi values different so teleconnection patterns are observed for each season strongest so signals appear in the winter with soi leading the height field by one to two seasons the time lead may he useful in prognostic applications the correlation in the summer is negligible the winter teleconnection pattern over the north pacific north america north atlantic sector is similar to that shown by bjerknes and others patterns for other seasons are also presented the statistical signifi

physical mechanisms of summer precipitation variations in the tarim basin in northwestern china abstractthe tarim basin tb in northwestern china is one of the most arid regions in the middle latitudes where water is scarce year round this study investigates the variations of summer precipitation in the tb and their association with water vapor fluxes and atmospheric circulation the results suggest that the variations of summer precipitation in the tb are dominated by the water vapor fluxes from the south and east although the long term mean water vapor mostly comes from the west the anomalous water vapor fluxes are closely associated with the meridional teleconnection pattern around 50 80 e and the zonal teleconnection pattern along the asian westerly jet in summer the meridional teleconnection connects central asia and the tropical indian ocean the zonal teleconnection resembles the silk road pattern the two teleconnections lead to negative height anomalies in central asia and positive height anomalies in the arabian sea and india and in northern central china the anomalous pressure g

a far reaching footprint of the tropical pacific meridional mode on the summer rainfall over the yellow river loop valley abstractover thousands of years the vicissitudes of the yellow river and surrounding geographic environment form a unique river loop in northwestern china namely the yellow river loop valley results from both observations and a climate model indicate that the summer rainfall over the yellow river loop valley region can be remotely controlled by sea surface temperature fluctuations in the eastern subtropical north pacific this far reaching teleconnection is achieved by an atmospheric wave train emanating from the eastern subtropical north pacific with a long traveling journey from the western to the eastern hemisphere furthermore it is found that the sst forcing pattern resembles the tropical pacific meridional mode a mode characterized by an interhemispheric temperature gradient and shift of the intertropical convergence zone in the eastern tropical pacific

mechanisms for the advanced asian summer monsoon onset since the mid to late 1990s abstractunderstanding the variability and change of monsoon onset is of utmost importance for agriculture planning and water management in the last three decades the asian summer monsoon onset asmo has remarkably advanced but the physical mechanisms underlying the change remain elusive since the overall asmo occurs in may this paper focuses on the change of mean fields in may and considers enhanced mean precipitation and monsoon westerly winds as signs of advanced asmo the results reveal that the advanced asmo mainly represents a robust decadal shift in the mid to late 1990s which is attributed to the mean state change in the pacific basin characterized by a grand la nina like pattern the la nina like mean state change controls the asmo through the westward propagation of rossby waves and its interaction with the asymmetric background mean states in the indian ocean and western pacific which intensifies the northern hemispheric perturbations and westerly winds intriguingly the abrupt decadal

extraordinary boulder transport by storm waves west of ireland winter 2013 2014 and criteria for analysing coastal boulder deposits abstract before and after photos of supratidal coastal boulder deposits cbd in the west of ireland show that storms in the winter of 2013 2014 transported boulders at elevations up to 29 m above high water and at inland distances up to 222 m among the clasts transported are eighteen weighing more than 50 t six of which exceed 100 t the largest boulder moved during those storms weighs a fairly astonishing 620 t the boulders moved in these recent storms provide pinning points for mapping storm wave energies on coasts their topographic positions mark elevations and distances inland reached by wave energies sufficient to dislocate those specific masses taken together the cbd data reveal general relationships that shed light on storm wave hydrodynamics these include a robust correlation inverse exponential between maximum boulder mass transported and emplacement height above high water the greater the elevation the smaller the maximum boulder size with a dependency exponent of about 0 2 times the elevation in metres there is a similar relationship although with a much smaller rate of change exponent 0 02 between boulder mass and distance inland which holds from the shoreline in to about 120 m coastal steepness calculated as the ratio of elevation to inland distance seems to exert the strongest control with an inverse power law relationship between maximum boulder mass and slope ratio the more gentle the topography the larger the moved boulders quantifying cbd dynamics helps us understand the transmission of wave energies inshore during high energy storm events the transported boulders documented here are larger than many of those interpreted to have been moved by tsunami in other locations which means that boulder size alone cannot be used as a criterion for distinguishing between tsunami and storm emplacement of cbd the biggest blocks up to 620 t are new maxima for boulder mass transported by storm waves we predict however that this record will not last long the 2013 2014 storms were strong but not extreme and there are larger boulders in these deposits that didn t move on this occasion bigger storms will surely move larger clasts and clasts at greater distances from the shoreline these measurements and relationships emphasise the extreme power of storm waves impacting exposed coastlines and require us to rethink the upper limits of storm wave energy at coasts

a role of the atlantic ocean in predicting summer surface air temperature over north east asia we assess the ability of the depresys3 prediction system to predict the summer jjas surface air temperature over north east asia depresys3 is based on a high resolution ocean atmosphere coupled climate prediction system 60 km in the atmosphere and 25 km in the ocean which is full field initialized from 1960 to 2014 26 start dates we find skill in predicting surface air temperature relative to a long term trend for 1 and 2 5 year lead times over north east asia the north atlantic ocean and eastern europe depresys3 also reproduces the interdecadal evolution of surface air temperature over the north atlantic subpolar gyre and north east asia for both lead times along with the strong warming that occurred in the mid 1990s over both areas composite analysis reveals that the skill at capturing interdecadal changes in north east asia is associated with the propagation of an atmospheric rossby wave which follows the subtropical jet and modulates surface air temperature from europe to eastern asia we hypothesise that this circumglobal teleconnection pattern is excited over the atlantic ocean and is related to atlantic multi decadal variability and the associated changes in precipitation over the sahel and the subtropical atlantic ocean this mechanism is robust for the 2 5 year lead time for the 1 year lead time the pacific ocean also plays an important role in leading to skill in predicting sat over northeast asia increased temperatures and precipitation over the western pacific ocean was found to be associated with a pacific japan like pattern which can affect east asia s climate

inter annual relationship between atlantic sea surface temperature anomalies and indian summer monsoon in this study the simultaneous inter annual relationships between sst anomalies over the northwest atlantic ocean and southwest monsoon rainfall over the monsoon core region have been examined using monthly sst and atmospheric data for the period 1951 2005 statistical analyses reveal significant inter annual simultaneous relationship between the sst anomalies over north atlantic and rainfall over the monsoon core region but with significant epochal variations the relationship has become stronger after mid 1970s when the el nino indian monsoon relationship has weakened positive sst anomalies over the north atlantic ocean shift the north atlantic jet northwards and the associated circulation changes in the upper troposphere influence indian monsoon through the circumglobal teleconnection across central asia the present study thus highlights the important role of north atlantic ocean as an important source of inter annual variability of the indian summer monsoon

boreholes in the middle devonian blastoid heteroschisma and their implications for gastropod drilling abstract boreholes in over 100 specimens of the devonian blastoid heteroschisma and the presence of the gastropod platyceras orthonychia sp attached to a specimen of heteroschisma subtruncatus hall 1858 suggest that platyceratid gastropods were capable of drilling their hosts at least as early as the middle devonian and thus represent the first known gastropods to have evolved this ability the presence of similar holes in numerous other devonian and mississippian blastoids and the occurrence of several additional examples of platyceratids attached to blastoids indicate that the interaction between gastropods and blastoids was not infrequent as in the case of the gastropod crinoid interaction this relationship is interpreted as having been parasitic rather than predatory the parasitic drilling platyceratids may have been a factor in the paleozoic precursor of the mesozoic marine revolution some of the anti predatory defenses of crinoids described from the late paleozoic may have been strategies of avoiding platyceratid infestation

origins of the 1988 north american drought the 1988 summer drought in the united states was the most extensive in many years because the drought developed in different places at different times not all regional effects can be traced to the same cause along the west coast and in the northwestern united states drought conditions developed during 1987 in association with the 1986 to 1987 el nino in the tropical pacific ocean record low rainfalls from april to june 1988 led to rapid development of drought in the north central united states strong anticyclonic conditions and a northward displaced jet stream in the upper atmosphere over north america throughout this period were only part of pronounced and distinctive wavetrain of anomalies in the atmospheric circulation that appeared to emanate from the tropical pacific below average sea surface temperatures along the equator in the pacific in the northern spring of 1988 combined with warmer than normal water from 10 degrees to 20 degrees n led to a northward displaced but still active intertropical convergence zone itcz southeast of hawaii results from a steady state planetarywave atmospheric model indicate that the atmospheric heating anomalies associated with the displaced itcz can force an anomalous wavetrain across north america similar to that observed land surface processes probably contributed to the severity and persistence of the drought however the large scale atmospheric circulation perturbations associated with natural variations in the coupled atmosphere ocean system in the tropical pacific were most likely the primary cause

a subtropical cyclonic gyre associated with interactions of the mjo and the midlatitude jet abstractthis paper describes a large cyclonic gyre that lasted several days in the northwest pacific during july 1988 cyclonic winds at 850 hpa extended beyond the 2000 km radius with a radius of maximum winds of 700 800 km the gyre exhibited clear skies within and north of its center active convection extended 4000 km in longitude to its south the madden julian oscillation mjo was in its active phase in the indian ocean prior to gyre formation consistent with earlier studies diabatic heating in the mjo was associated with an anomalous upper tropospheric westerly jet over the northeast asian coast and a jet exit region over the northwest pacific repeated equatorward wave breaking events developed downwind of the jet exit region one such event left behind a region of lower tropospheric cyclonic vorticity and convection in the subtropics that played a key role in the gyre formation a second wave breaking event produced strong subsidence north of the mature gyre that contributed to its convective a

palaeocommunities diversity and sea level change from middle eocene shell beds of the paris basin the middle eocene interval at some paris basin localities was studied through high resolution stratigraphy abundance data 499 species 37 719 individuals on the distribution of molluscs collected at 12 shell beds of the middle lutetian and lower bartonian formed the basis for a palaeoecological study the middle lutetian succession is subdivided into several elementary depositional sequences eds interpreted as the product of relative sea level change species abundance distributions are better correlated with eds than with geographical locality suggesting that sea level played an important role in the distribution of palaeocommunities diversities were compared with analogous data from modern subtropical and warm temperate intertidal and subtidal communities we found that sea level variation is responsible for a major change in the upper part of the middle lutetian succession leading from high to low diversity palaeocommunities from base to top sampled palaeocommunities indicate a transition from high energy and mesotrophic eds 2 to oligotrophic low energy conditions of a sandy lower shoreface eds 4 to an upper shoreface eds 5 and lower bartonian the last with mangroves and a seagrass cover notwithstanding the lutetian cooling we found that subtropical conditions reached as far north as the paris basin our study suggests that climatic fluctuations might be obscured by facies control

mechanisms of hemispherically symmetric climate variability inspired by paleoclimate evidence that much past climate change has been symmetric about the equator the causes of hemispherically symmetric variability in the recent observational record are examined using the national centers for environmental prediction national center for atmospheric research reanalysis dataset and numerical models it was found that the dominant cause of hemispherically symmetric variability is the el nino southern oscillation during an el nino event the tropics warm at all longitudes and the subtropical jets in both hemi spheres strengthen on their equatorward flanks poleward of the tropical warming there are latitude belts of marked cooling extending from the surface to the tropopause in both hemispheres at all longitudes and in all seasons the midlatitude cooling is caused by changes in the eddy driven mean meridional circulation changes in the transient eddy momentum fluxes during an el nino event force upper tropospheric ascent in midlatitudes through a balance between the eddy fluxes and the coriolis torque the eddy driven ascent causes anomalous adiabatic cooling which is primarily balanced by anomalous diabatic heating using a quasigeostrophic spherical model forced by an imposed surface eddy disturbance of chosen wave number and frequency it is shown that the anomalous eddy momentum fluxes are caused by the impact that the changes in the tropically forced subtropical jets have on the propagation in the latitude height plane of transient eddies changes in zonal winds and associated changes in the meridional gradient of potential vorticity create an anomalous region of low meridional wavenumber in the midlatitudes that refracts waves away both poleward and equatorward tropical forcing of variability in the eddy driven mean meridional circulation is another way in addition to rossby wave teleconnections whereby the tropics can influence extratropical climate unlike teleconnections this mechanism causes climate variability that has strong zonally and hemispherically symmetric components and operates throughout the seasonal cycle

three pattern decomposition of global atmospheric circulation part i decomposition model and theorems in order to study the interactions between the atmospheric circulations at the middle high and low latitudes from the global perspective the authors proposed the mathematical definition of three pattern circulations i e horizontal meridional and zonal circulations with which the actual atmospheric circulation is expanded this novel decomposition method is proved to accurately describe the actual atmospheric circulation dynamics the authors used the ncep ncar reanalysis data to calculate the climate characteristics of those three pattern circulations and found that the decomposition model agreed with the observed results further dynamical analysis indicates that the decomposition model is more accurate to capture the major features of global three dimensional atmospheric motions compared to the traditional definitions of rossby wave hadley circulation and walker circulation the decomposition model for the first time realized the decomposition of global atmospheric circulation using three orthogonal circulations within the horizontal meridional and zonal planes offering new opportunities to study the large scale interactions between the middle high latitudes and low latitudes circulations

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 sea surface temperatures in forcing circulation anomalies driving u s great plains pluvial years abstractin the u s great plains gp diagnosing precipitation variability is key in developing an understanding of the present and future availability of water in the region building on previous

the meridional displacement of the summer asian jet silk road pattern and tropical sst anomalies abstractthe silk road pattern srp which depicts the teleconnection pattern along the asian jet has been extensively investigated and commonly described as the leading mode of upper tropospheric meridional wind anomalies in summer in this study the srp is identified as having a significant relationship with the meridional displacement of the asian jet jmd which manifests as the leading mode of upper tropospheric zonal wind anomalies this significant relationship is confirmed by the correlation coefficient between the indices for jmd and srp which is 0 39 and reaches statistical significance at the 0 01 level when the asian jet is in a northward southward displacement the phase of srp tends to be shown as anticyclonic cyclonic anomalies over western asia and east asia and cyclonic anticyclonic anomalies over europe and central asia the authors propose an internal atmospheric mechanism for this relationship in addition it is found that the jmd is significantly affected by the tropical s

equatorward increase in naticid gastropod drilling predation on infaunal bivalves from brazil with paleontological implications abstract understanding the influence of spatial variation on temporal trends is important for interpreting evolutionary patterns of predation in the fossil record geographic data on naticid gastropod drilling predation are contradictory and mostly limited to the northern hemisphere this study examines latitudinal variation in drilling on 24 000 beach collected recent bivalves from 6 s to 34 s in brazil twenty eight localities representing 16 latitudes were sampled in the brazilian and argentinean provinces further subdivided into four smaller ecoregions northeastern brazil eastern brazil southeastern brazil rio grande analyses focused on bivalves exhibiting infaunal life habits increased drilling equatorward was observed at the assemblage level across several spatial scales localities latitudes ecoregions provinces taxon level analyses for eight genera drilled across multiple ecoregions generally indicated greater drilling among lower latitudes size standardization did not affect patterns at the genus level an equatorward increase in drilling was documented also upon restricting the data to localities characterized primarily by softer substrates fine to medium grained sediments and in limiting data to samples obtained by a single collecting strategy minimizing concerns regarding the influence of local environmental variation and different methodologies on latitudinal patterns in drilling latitudinal patterns in drilling may be related to temperature and seasonality in influencing metabolic rates as well as diversity and predator prey size distributions the results of this study do not correspond to existing patterns previously described for western atlantic molluscan assemblages of the northern hemisphere however they may help explain temporal patterns in the fossil record of naticid predation