role of seasonal transitions and the westerlies in the interannual variability of the east asian summer monsoon precipitation a recent hypothesis holds that changes to the east asian summer rainfall are characterized by changes in the timing and duration of its intraseasonal stages controlled by the meridional position of the westerlies relative to the tibetan plateau this hypothesis is examined in the context of the leading mode of east asian summer july aug rainfall one phase of this tripole mode characterized by less rainfall over central eastern china and increased rainfall over northeastern and southeastern china is tied to an earlier termination of meiyu that results in a significantly shorter meiyu and longer midsummer stage this phase also exhibits an earlier northward transition of the westerlies to the north of the plateau essentially mirroring the changes to precipitation seasonality the reverse does not hold true for the opposite phase our results show direct observational evidence for the meridional position of the westerlies to control east asian summer monsoon seasonality

dipole structure of interannual variations in summertime tropical cyclone activity over east asia the present study examines variations in summertime july september tropical cyclone tc activity over east asia during the period 1951 2003 to represent tc activity a total of 853 tc best tracks for the period were converted to tc passage frequencies tpfs within 5 5 latitude longitude grids tpfs are defined as the percentage values obtained by dividing the number of tc appearances in each grid box by the total number of tcs each year empirical orthogonal function analysis of the tpf showed three leading modes two tropical modes that represent the long term trend and the relationship with enso and one midlatitude mode that oscillates between south of korea and southeast of japan with an interannual time scale the latter proved to be the most remarkable climatic fluctuation of summertime tc activity in the midlatitudes and is referred to as the east asian dipole pattern eadp in this paper anomalous atmospheric flows directly connected to the eadp are an enhanced anticyclonic cyclonic circulation centering around japan when the tpf is high south of korea southeast of japan thereby showing an equivalent barotropic structure in the entire troposphere this regional circulation anomaly varies in conjunction with the zonally oriented quasi stationary rossby wave train in the upper troposphere this wave train is meridionally trapped in the vicinity of the summer mean jet stream therefore the mean jet stream alters its internal meandering structure according to the phase of the wave train

drought in late spring of south china in recent decades late spring 21 april 20 may precipitation to the south of the yangtze river in china along the east asian front is a salient feature of the global climate the present analysis reveals that during 1958 2000 south china 26 31 n 110 122 e has undergone a significant decrease in late spring precipitation since the late 1970s the sudden reduction of the precipitation concurs with a notable cooling in the upper troposphere over the central china 30 40 n 95 125 e the upper level cooling is associated with an anomalous meridional cell with descending motions in the latitudes 26 35 n and low level northerly winds over southeastern china 22 30 n 110 125 e causing deficient rainfall over south china the late spring cooling in the upper troposphere over the central china is found to strongly link to the north atlantic oscillation nao in the preceding winter during winters with a positive nao index the upper tropospheric cooling occurs first to the north of the tibetan plateau in early middle spring then propagates southeastward to central china in late spring it is suggested that the interdecadal change of the winter nao is the root cause for the late spring drought over south china in recent decades

rock magnetism of remagnetized carbonate rocks another look authigenic formation of fine grained magnetite is responsible for widespread chemical remagnetization of many carbonate rocks authigenic magnetite grains dominantly in the super paramagnetic and stable single domain size range also give rise to distinctiverock magnetic prop erties now commonly used as a fingerprint of remagnetization we re examine the basis of this association in terms of magnetic mineralogy and particle size distribution in remagnetized carbon ates having these characteristic rock magnetic properties including wasp waisted hysteresis loops high ratios of anhysteretic remanence to saturation remanence and frequency dependent susceptibility new measurements on samples from the helderberg group allow us to quantify the proportions of superparamagnetic stable single domain and larger grains and to evaluate the mineralogical composition of the remanence carriers the dominant magnetic phase is magnetite like with sufficient impurity to completely suppress the verwey transition particle sizes are extremely fine approximately 75 of the total magnetite content is superparamagnetic at room temperature and almost all of the rest is stable single domain although it has been pro posed that the single domain magnetite in these remagnetized carbonates lacks shape anisotropy and is therefore controlled by cubic magnetocrystalline anisotropy we have found strong exper imental evidence that cubic anisotropy is not an important underlying factor in the rock magnetic signature of chemical remagnetization the usefulness of a palaeomagnetic remanence is directly related to the accuracy with which its age is known e g van der voo 1990 primary remanence acquiredduringorverysoonafterrockformation pro videsdirectinformationonpalaeofieldorientationand strengthatthattime thepossibilityofpartialorcom plete remagnetization at a later time complicates palaeomagneticinterpretation ashaslongbeenrecog nized e g graham 1949 every robust palaeomag netic study must therefore include some effort to constrain the ages of identified components of the natural remanent magnetization nrm relative dating with respect to sedimentary processes struc tural tilting or cross cutting relationships is the basis of the classical geometric palaeomagnetic tests fold test and conglomerate test graham 1949 baked contact test everitt clegg 1962 unconformity test kirschvink 1978 the special circumstances required for application of these tests are often not available however or positive test results may providerelativelylooseconstraintsallowingmagneti zation ages that significantly post date the age of the rock formation as a result other evidence although generally more indirect becomes essential in evaluating the age origin and significance of nrm components such evidence commonly includes petrographic observations isotopic andgeo chemical data and rock magnetic characterization by their very existence magnetic overprints provide evidence of some process or event of

potbellies wasp waists and superparamagnetism in magnetic hysteresis because the response of a magnetic substance to an applied field depends strongly on the physical properties of the material much can be learned by monitoring that response through what is known as a magnetic hysteresis loop the measurements are rapid and quickly becoming part of the standard set of tools supporting paleomagnetic research yet the interpretation of hysteresis loops is not simple it has become apparent that although classic single domain pseudo single domain and multidomain loops described in textbooks occur in natural samples loops are frequently distorted having constricted middles wasp waisted loops or spreading middles and slouching shoulders potbellies such complicated loops are often interpreted in oversimplified ways leading to erroneous conclusions the physics of the problem have been understood for nearly half a century yet numerical simulations appropriate to geological materials are almost unavailable in this paper we discuss results of numerical simulations using the simplest of systems the single domain superparamagnetic sd sp system examination of the synthetic hysteresis loops leads to the following observations 1 wasp waisting and potbellies can easily be generated from populations of sd and sp grains 2 wasp waisting requires an sp contribution that saturates quickly resulting in a steep initial slope and potbellies require low initial slopes the sp contribution approaching saturation at higher fields the approach to saturation is dependent on volume hence the cube of grain diameter therefore there is a very strong dependence of hysteresis loop shape on the assumed threshold size 3 we were unable to generate potbellies using an sp sd threshold size as large as 30 nm and wasp waists cannot be generated using a threshold size as small as 8 nm the occurrence of both potbellies and wasp waists in natural samples is consistent with a room temperature threshold size of some 15 nm 5 4 simulations using a threshold size of 15 20 nm with populations dominated by sp grain sizes that is with a small number of sd grains produce synthetic hysteresis loops consistent with measured hysteresis loops and transmission electron microscopic observations from submarine basaltic glass 5 simulations and measurements using two populations with distinct coercivity spectra can also generate wasp waisted loops a relatively straightforward analysis of the resulting loops can distinguish the latter case from wasp waisting resulting from sp sd behavior

calibration of magnetic granulometric trends in oceanic basalts abstract the validity of magnetic granulometric estimates relies heavily on the ability to distinguish ultrafine particles from coarser grains for example populations with dominantly superparamagnetic sp or multidomain md grains both are characterized by low remanence and coercivity and distinguishing these endmembers may provide valuable clues to the origin of magnetization in the intervening stable single domain sd size range the natural grain size variations associated with variable cooling rates in submarine lavas provide a rare opportunity for examining progressive changes in average magnetic grain size from sp sd mixtures in submarine basaltic glass to sd md mixtures in flow interiors based on microanalysis and rock magnetic measurements on pillow basalt samples dredged from the flanks of the mid atlantic ridge ages

magnetic hysteresis as a function of low temperature for deep sea basalts containing large titanomagnetite grains inference of domain state and controls on coercivity hysteresis loops to 1200 oe 95 ka m 1 are measured between 295 and 105 k for two deep sea basalts dsdp legs 34 and 37 containing large 200 m unexsolved titanomagnetite grains the curie points electron microprobe analyses and saturation magnetizations of the magnetic grains are the same as for synthetic titanomagnetite xfe2tio4 1 x fe3o4 with x 0 6 as temperature is lowered from 295 to 190 k coercive force hc slowly rises from 40 to 95 oe 3 2 to 7 6 ka m 1 approximately in proportion to the rise in the magnetostriction constant presumably hc is controlled by through internal stresses impeding domain wall motion as expected of multidomain grains the ratio of saturation remanence to saturation magnetization in 1200 oe 95 ka m 1 cycles jr js rises approximately in proportion to hc with a constant of proportionality consistent with titanomagnetite x 0 6 as temperature is lowered from 190 to 120 k hc rises rapidly to 400 oe 32 ka m 1 as a roughly linear function of the

unmixing magnetic remanence curves without a priori knowledge summary many of the natural materials studied in rock and environmental magnetism contain a mixed assemblage of mineral grains with a variety of different origins mathematical decomposition of the bulk magnetic mineral assemblage into populations with different properties can therefore be a source of useful environmental information previous investigations have shown that such unmixing into component parts can provide insights concerning source materials transport processes diagenetic alteration authigenic mineral growth and a number of other processes a new approach will be presented that performs a linear unmixing of remanence data into coercivity based end members using only a minimal number of assumptions a non negative matrix factorization nmf algorithm for unmixing remanence data into constituent end members is described with case studies to demonstrate the utility of the approach the shape of the end members and their abundances obtained by nmf is based solely on the variation in the measured data set and there is no requirement for mathematical functions or type curves to represent individual components therefore in contrast to previous approaches that aimed to unmix curves into components corresponding to individual minerals and domain states nmf produces a genetically more meaningful decomposition showing how a data set can be represented as a linear sum of invariant parts it has been found that the nmf algorithm performs well for both absolute and normalized remanence curves with the capacity to process thousands of measured data points rapidly

why the western pacific subtropical high has extended westward since the late 1970s the western pacific subtropical high wpsh is closely related to asian climate previous examination of changes in the wpsh found a westward extension since the late 1970s which has contributed to the inter decadal transition of east asian climate the reason for the westward extension is unknown however the present study suggests that this significant change of wpsh is partly due to the atmosphere s response to the observed indian ocean western pacific iwp warming coordinated by a european union s sixth framework programme understanding the dynamics of the coupled climate system dynamite five agcms were forced by identical idealized sea surface temperature patterns representative of the iwp warming and cooling the results of these numerical experiments suggest that the negative heating in the central and eastern tropical pacific and increased convective heating in the equatorial indian ocean maritime continent associated with iwp warming are in favor of the westward extension of wpsh the sst changes in iwp influences the walker circulation with a subsequent reduction of convections in the tropical central and eastern pacific which then forces an enso gill type response that modulates the wpsh the monsoon diabatic heating mechanism proposed by rodwell and hoskins plays a secondary reinforcing role in the westward extension of wpsh the low level equatorial flank of wpsh is interpreted as a kelvin response to monsoon condensational heating while the intensified poleward flow along the western flank of wpsh is in accord with sverdrup vorticity balance the iwp warming has led to an expansion of the south asian high in the upper troposphere as seen in the reanalysis

subsolidus evolution and alteration of titanomagnetite in ocean ridge basalts from deep sea drilling project ocean drilling program hole 504b9 leg 83 implications for the timing of magnetization magnetic minerals in six samples of oceanic basalts of the transition zone and upper sheeted dikes from deep sea drilling project ocean drilling program dsdp odp hole 504b leg 83 were studied by methods of rock magnetism and transmission electron microscopy tem tem observations showed that the magnetic mineral in these basalts is end member magnetite tmo of extremely fine grain size 30 100 nm primarily in the range of pseudosingle domain magnetite consistent with the rock magnetic properties including hysteresis parameters curie temperature and low temperature measurements verwey transition magnetite formed by two different processes 1 oxidation exsolution true exsolution and hydrothermal alteration and 2 oxidation exsolution a second stage of oxidation exsolution and hydrothermal alteration the primary titanomagnetite tm60 70 that crystallized from the melt thus evolved to end member magnetite coexisting with titanite sphene kassite ulvospinel tm 87 and ilmenite on a submicroscopic scale on the basis of the formation mechanisms of the magnetic carrier the primary titanomagnetite tm 60 with curie temperature of 180 c did not acquire thermoremanent magnetization trm in these basalts instead the ti bearing magnetite tm 10 20 that formed as oxidized or exsolved lamellae acquired its first thermal chemical remanent magnetization crm at 500 400 c during subsolidus cooling upon the onset of hydrothermal alteration the recrystallized end member magnetite acquired a second crm the natural remanent magnetization of the basalts from the transition zone and upper sheeted dikes is therefore characteristic of crms that were acquired when titanomagnetite altered in part to magnetite during subsolidus cooling and hydrothermal alteration close to the ridge axis

indian ocean capacitor effect on indo western pacific climate during the summer following el nino significant climate anomalies persist through the summer june august after el nino dissipates in spring over the equatorial pacific they include the tropical indian ocean tio sea surface temperature sst warming increased tropical tropospheric temperature an anomalous anticyclone over the subtropical northwest pacific and increased mei yu baiu rainfall over east asia the cause of these lingering el nino effects during summer is investigated using observations and an atmospheric general circulation model gcm the results herein indicate that the tio warming acts like a capacitor anchoring atmospheric anomalies over the indo western pacific oceans it causes tropospheric temperature to increase by a moist adiabatic adjustment in deep convection emanating a baroclinic kelvin wave into the pacific in the northwest pacific this equatorial kelvin wave induces northeasterly surface wind anomalies and the resultant divergence in the subtropics triggers suppressed convection and the anomalous anticyclone the gcm results support this kelvin wave induced ekman divergence mechanism in response to a prescribed sst increase over the tio the model simulates the kelvin wave with low pressure on the equator as well as suppressed convection and the anomalous anticyclone over the subtropical northwest pacific an additional experiment further indicates that the north indian ocean warming is most important for the kelvin wave and northwest pacific anticyclone a result corroborated by observations these results have important implications for the predictability of indo western pacific summer climate the spatial distribution and magnitude of the tio warming rather than simply whether there is an el nino in the preceding winter affect summer climate anomalies over the indo western pacific and east asia

grain size dependent paleointensity results from very recent mid oceanic ridge basalts 1 we report paleointensity analyses on a suite of four samples from two axial zero age mid oceanic ridge basalt flows from the east pacific rise paleointensity experiments have been performed on several profiles each consisting of a batch of small millimeter scale subsamples going from the rapidly cooled glassy margin to the interior the coe version of the thellier double heating procedure was used with back checks performed after every other heating step most of the samples show very good behavior i e constant ratio between the lost and acquired magnetization through a large temperature range quality factor usually above 10 and positive checks which lead to unambiguous paleointensity determinations paleointensities obtained on glasses reported here and in a previously published study are very consistent and reproducible and in agreement with expected in situ values of earth s magnetic field intensity however results found within the crystalline part of the samples show values that are considerably up to 50 higher than expected these variations seem to be correlated with the cooling history of the samples and appear to be universal since all samples exhibit the same intriguing pattern an extensive study of magnetic properties allows us to link this incongruent behavior to 1 the presence of multidomain effects and 2 the cooling rate difference between laboratory experiments and in situ cooling

the early 1950s regime shift in temperature in taiwan and east asia a summer climate regime shift in temperature in taiwan and east asia during the early 1950s was identified in this study the event was characterized by a cooling land warming ocean dipole in east asia and the western north pacific marking the decreasing land sea thermal contrast from the 1940s to the 1950s the corresponding sea surface temperature sst anomaly was characterized by the sign flipping of a north south dipole in the western north pacific from north cool south warm to north warm south cool indicating a weakening north south sst gradient in the area the corresponding change in mean sea level pressure was characterized by the rising pressure in continental east asia and the philippine sea and the falling pressure over the extratropical western north pacific to the east of japan this change was the reflection of a weakening thermal low in the continental east asia a weakening monsoon trough in the tropical western north pacific a strengthening and southwestward expanding ridge in the subtropical western north pacific and a deepening mid latitude trough over eastern china and japan the phase reversal of the sst anomaly in the western north pacific exhibited the characteristics of the pacific decadal oscillation pdo but lagged behind the phase reversal of the pdo in the extratropical north pacific by several years the connection with the pdo is speculated although the mechanism is not understood

magnetic hysteresis in young mid ocean ridge basalts dominant cubic anisotropy magnetic hysteresis data from young mid ocean ridge basalts include samples with saturation remanence to saturation magnetization mrs ms ratios greater than 0 5 the theoretical limit for an assemblage of single domain grains with uniaxial anisotropy under the usual assumption of dominant uniaxial anisotropy the narrow single domain grain size distribution implied by these high mrs ms values is difficult to reconcile with petrographic and remanence data that suggest the presence of larger multidomain grains dominant cubic anisotropy provides a plausible explanation for the high mrs ms ratios and if generally valid requires reinterpretation of granulometric and domain state inferences made from hysteresis data

interannual change in summertime precipitation over northeast asia 1 the summertime precipitation over northeast asia mongolia and inner mongolia increased from 1980 to the mid 1990s and low precipitation summers continued for 4 years from 1999 a vegetation index based on satellite observations shows a similar interannual change the first eof mode of the interannual change of july precipitation shows a seesaw pattern between northeast asia and siberia and the time coefficient represents the summertime precipitation change over northeast asia this mode is associated with rossby waves propagating eastward over the eurasian continent which accompany anomalous meridional winds over northeast asia and siberia resulting in anomalous vertical flows the vertical flows over these regions are connected with each other through the meridional circulation which contributes to form the seesaw pattern by suppressing or enhancing the precipitation

interannual and interdecadal variability of the summertime western north pacific subtropical high 1 the western north pacific subtropical high wnpsh in summer exhibits significant 2 3 years and 3 5 years oscillations with interdecadal variability the 2 3 year oscillation is most evident after 1990 it is accompanied by anomalous meridional overturning circulation characterized by warm sst anomalies ssta and ascending motion in the maritime continent and anomalous descending motion near the philippine sea and by evolving warm to cold ssta in the central eastern pacific from the preceding winter to the summer the 3 5 year oscillation is most pronounced during the 1980s it is accompanied by anomalous descending motion over the maritime continent and warm ssta in the central eastern equatorial pacific that persists from the preceding winter to the summer the complementary cooling and descending motion in the western pacific are related to anomalous east west circulation associated with enso

decadal changes of meiyu rainfall around 1991 and its relationship with two types of enso 1 this study investigates meiyu june july rainfall from 1980 to 2000 over yangtze huaihe river valley yhrv and reveals a decadal change around 1991 with a seesaw like distribution this decadal change is closely associated with negative phase of preceding winter el nino southern oscillation enso modoki em in the pre 1991 epoch and positive phase of conventional enso ce in the post 1991 epoch in response to negative em pre 1991 epoch the source of water vapor is western north pacific associated with the eastward retreat of western pacific subtropical high wpsh and the northward shift of east asian westerly jet eawj on the other hand in response to positive ce post 1991 epoch water vapor generally comes from the south china sea associated with the enhancement and westward advance of the wpsh and southward shift of the eawj two possible mechanisms are proposed to explain the relationship between preceding winter sea surface temperature sst and meiyu rainfall over yhrv in the two epochs in the pre 1991 epoch due to enhanced precipitation solar radiation decreases resulting in sst cooling over western north pacific in meiyu period an anomalous anticyclone associated with the sst cooling suppresses precipitation over northern part of yhrv meanwhile an anomalous cyclone accompanied with the anticyclone locates over east china sea and brings more precipitation to the southern part of yhrv in the post 1991 epoch the persistent simultaneous warming in eastern equatorial pacific and indian ocean leads to abundant moisture brought to southern china further analysis suggests that the two types of enso have asymmetric features with respect to the impact of their positive and negative phases on the seesaw like meiyu rainfall which is closely related with em la nina ce el nino in the pre 1991 epoch post 1991 epoch

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

petrology and rock magnetism of the gabbro of troodos ophiolite abstract in order to determine the nature of remanence carriers of the layered gabbro of the troodos ophiolite cyprus we report optical and electron microscopic observations together with rock magnetic and paleomagnetic experiments above all the study aims to understand and clarify the time of magnetic acquisition relative to the brittle deformation of the oceanic crust manifested by the ridge transform intersection solea graben and the arakapas transform petrographic examination of pyroxene grains revealed isolated magnetite inclusions ranging in size from single domain sd to multi domain md and in addition md pyrrhotite inclusions residing in veins and cracks thermal demagnetization and thermomagnetic procedures indicate two components low and high temperature we argue that the low temperature component the sd magnetite inclusions exsolved in pyroxene are the dominant carriers of magnetic remanence in troodos gabbro the initial formation of these inclusions occurred via exsolution reaction at temperatures between 520 and 850 c above the curie temperature of pure magnetite during the solidification of the magma therefore acquisition of remanent magnetization of the troodos gabbro took place during the earliest stages of crustal accretion before any brittle deformation associated with the spreading ridge and the transform fault occurred

the asian summer monsoon an intercomparison of cmip5 vs cmip3 simulations of the late 20th century the boreal summer asian monsoon has been evaluated in 25 coupled model intercomparison project 5 cmip5 and 22 cmip3 gcm simulations of the late twentieth century diagnostics and skill metrics have been calculated to assess the time mean climatological annual cycle interannual variability and intraseasonal variability progress has been made in modeling these aspects of the monsoon though there is no single model that best represents all of these aspects of the monsoon the cmip5 multi model mean mmm is more skillful than the cmip3 mmm for all diagnostics in terms of the skill of simulating pattern correlations with respect to observations additionally for rainfall convection the mmm outperforms the individual models for the time mean the interannual variability of the east asian monsoon and intraseasonal variability the pattern correlation of the time pentad of monsoon peak and withdrawal is better simulated than that of monsoon onset the onset of the monsoon over india is typically too late in the models the extension of the monsoon over eastern china korea and japan is underestimated while it is overestimated over the subtropical western central pacific ocean the anti correlation between anomalies of all india rainfall and nino3 4 sea surface temperature is overly strong in cmip3 and typically too weak in cmip5 for both the enso monsoon teleconnection and the east asian zonal wind rainfall teleconnection the mmm interannual rainfall anomalies are weak compared to observations though simulation of intraseasonal variability remains problematic several models show improved skill at representing the northward propagation of convection and the development of the tilted band of convection that extends from india to the equatorial west pacific the mmm also well represents the space time evolution of intraseasonal outgoing longwave radiation anomalies caution is necessary when using gpcp and cmap rainfall to validate 1 the time mean rainfall as there are systematic differences over ocean and land between these two data sets and 2 the timing of monsoon withdrawal over india where the smooth southward progression seen in india meteorological department data is better realized in cmap data compared to gpcp data

diagenetic sources of stable remanence in remagnetized paleozoic cratonic carbonates a rock magnetic study hysteresis measurements lowrie fuller tests cisowski tests and low temperature demagnetization experiments on samples of the knox dolomite trenton limestone and onondaga limestone indicate that the remanence in these remagnetized carbonate units resides principally in single domain magnetite in contrast to previous interpretations volumetrically however a significant fraction of the magnetite is coarser grained as previous scanning electron microscopic work on magnetic extracts has shown these conclusions are based mainly on the characteristic wasp waisted shape of the hysteresis loops and on the anomalously high ratios of remanent coercivity to bulk coercivity both of which clearly indicate a bimodal distribution of coercivities grain sizes the magnetization is controlled mainly by cubic magnetocrystalline anisotropy consistent with the spheroidal particles commonly observed in extracts hysteresis trends show that especially the finest particles lack shape anisotropy in view of these conclusions the two components of natural remanence in these rocks are interpreted as 1 a late paleozoic kiaman chemical remanence carried by single domain diagenetic magnetite and 2 a cenozoic thermoviscous overprint residing principally in coarser pseudosingle domain and multidomain magnetite also of late paleozoic diagenetic origin

response of northern hemisphere storm tracks to indian western pacific ocean warming in atmospheric general circulation models with 40 years integration output of two atmospheric general circulation models gamil iap and hadam3 ukmo forced with identical prescribed seasonally varying sea surface temperature this study examines the effect of the observed indian western pacific ocean iwp warming on the northern hemisphere storm tracks both models indicate that the observed iwp warming tends to cause both the north pacific storm track npst and the north atlantic storm track nast to move northward such a consistent effect on the two storm tracks is closely associated with the changes in the low level atmospheric baroclinicity high level jet stream and upper level geopotential height the iwp warming can excite a wavelike circum global teleconnection in the geopotential height that gives rise to an anticyclonic anomaly over the midlatitude north pacific and a positive phase nao anomaly over the north atlantic these geopotential height anomalies tend to enhance upper level zonal westerly winds north of the climatological jet axes and increase low level baroclinicity and eddy growth rates thus favoring transient eddy more active north of the climatological storm track axes responsible for the northward shift of the both storm tracks the iwp warming induced northward shift of the nast is quite similar to the observed suggesting that the iwp warming can be one of the key factors to cause decadal northward shift of the nast since the 1980s however the iwp warming induced northward shift of the npst is completely opposite to the observed implying that the observed southward shift of the npst since the 1980s would be primarily attributed to other reasons although the iwp warming can have a cancelling effect against those reasons

comment on detecting uniaxial single domain grains with a modified irm technique by r mitra l tauxe and j s gee summary in a recent article mitra et al 2011 propose a modified irm technique to identify the symmetry of magnetic anisotropy in single domain particle ensembles they apply this technique to support an earlier suggestion that single domain grains in young mid ocean ridge basalts morb exhibit multiaxial anisotropy here it is shown that the design of their measurement is flawed in that they do not take into account that the outcome essentially depends on the initial demagnetization state of the sample before the experiment and on the coercivity distribution of the sample because all morb specimens measured by mitra et al 2011 carried their original nrm which closely resembles a thermally demagnetized state their measurements first of all reflect the coercivity distributions and domain states of the samples and contain little or no information about the symmetry of the magnetic anisotropy all arguments previously put forward in favour of a dominant uniaxial anisotropy in morb are therefore still valid

the two interannual variability modes of the western north pacific subtropical high simulated by 28 cmip5 amip models using the output of the atmospheric model intercomparison project amip experiments of 28 models from the fifth phase of the coupled model intercomparison project cmip5 the models performances in the simulation of the two dominant interannual variability modes of the western north pacific subtropical high wnpsh are investigated in the observation the positive phases of these two modes feature an anomalous anticyclone over the western north pacific wnp but the first mode m1 is closely connected with the sea surface temperature sst anomalies over the tropical indian ocean tio the maritime continent mc and the equatorial central pacific cp while the second mode m2 is closely connected with the sst anomalies over the wnp the m1 is well captured by the cmip5 amip models forced by the historical sst suggesting the m1 is an sst forced mode the cmip5 amip models capture the close relationship of the m1 with the sst anomalies over the tio the mc and the cp the forcing mechanisms of m1 in the cmip5 amip models are consistent with the observation including a kelvin wave emanating from the tio and a local hadley circulation originating from the mc different from the high reproducibility of the m1 the m2 is only moderately reproduced by the multi model ensemble mme mean of the cmip5 amip models the simulated anomalous wnpsh of the m2 is weaker and shifts southwestward in the mme and many individual models compared to the observation among the five anomalous wnpsh years associated with the m2 the mme captures the anomalous wnpsh only in 1993 and 1994 but not in 1980 1981 and 1987 the partial reproducibility of the m2 by the cmip5 amip models suggests the m2 is neither a pure atmospheric internal mode nor a pure sst forced mode the observed close relationship between the anomalous wnpsh and the wnp sst anomalies is underestimated by the cmip5 amip models suggesting the local sst wnpsh relationship may depend on the air sea interaction over the wnp

new paleomagnetic results from basaltic drill cores of the nauru basin western pacific tectonic and magnetostratigraphic implications abstract the voluminous volcanic eruptions in the nauru basin western pacific have long been regarded as important research targets for tectonic history of the pacific plate and for the widespread cretaceous volcanic activity in the western pacific the nauru basin volcanic rocks were recovered at site 462 by deep sea drilling project dsdp legs 61 and 89 where more than 600 m of lavas and sills were drilled thereby making it the deepest penetration into crust of cretaceous age in the pacific ocean for paleomagnetism this section represents a unique possibility for averaging out secular variation to obtain a reliable paleolatitude estimate however previous paleomagnetic studies have only been subjected to alternating field af demagnetization on several core samples thus unable to provide comprehensive understanding on the paleolatitude of the basin the work reported here aims to determine the cretaceous paleomagnetic paleolatitude for the pacific plate and define the magnetostratigraphy for the basaltic sections drilled in the nauru basin a total of 391 basaltic rock samples were carefully re sampled from dsdp sites 462 and 462a stepwise thermal and af demagnetizations have isolated characteristic components in the majority of the samples the most important findings from this study include 1 two normal and one reversed polarity intervals are identified in site 462 and six normal and six reversed polarity intervals are found in site 462a although possible erroneous markings of the opposite azimuth for some reversed polarity cores during the dsdp coring cannot be completely ruled out 2 based on previous radiometric ages the magnetostratigraphic correlations with the geomagnetic polarity time scale gpts indicate that the lower basaltic flow unit in site 462a began to erupt at least before 130 ma no correlation is available for the upper sill unit 3 paleosecular variation for the lower flow unit has been sufficiently averaged out whereas bias may exist for that of the upper sill unit 4 the calculated mean inclination of 50 for the lower flow unit yields a paleolatitude of 30 8 s for the nauru basin at the time of emplacement this value is well to the north of suggested location in plate reconstruction models suggesting that there has been a significant amount of apparent polar wander of the nauru basin and pacific plate since 130 ma in addition the paleolatitude for the nauru basin is 7 further south and the basin s age is more than 10 my older than those of the ontong java plateau ojp which suggest that the volcanic eruptions of the lower flows in the nauru basin are unlikely related to the emplacement of the ontong java plateau

shift in the summer rainfall over the yangtze river valley in the late 1970s 1 the summer rainfall over the middle lower valley of the yangtze river and over the whole eastern china experienced a notable regime shift in about 1979 this change is consistent with a simultaneous jump like change in the 500 hpa geopotential height 500 over the northern pacific the rainfall over the yangtze river valley is closely related to the 500 averaged over the area 20 25 n 125 140 e with a correlation coefficient of 0 66 for the period 1958 1999 since 1980 the subtropical northwestern pacific high snph has enlarged intensified and extended southwestward the changes in the snph are strongly associated with the variations of the sea surface temperatures ssts of the eastern tropical pacific and tropical indian ocean the anomalies of these ssts responsible primarily for the shift of the summer rainfall over the yangtze river through the changes in snph precede the 500 signals with different leading times

interannual and interdecadal variations of the east asian summer monsoon and tropical pacific ssts part i roles of the subtropical ridge the interannual relationship between the east asian summer monsoon and the tropical pacific ssts is studied using rainfall data in the yangtze river valley and the ncep reanalysis for 1951 96 the datasets are also partitioned into two periods 1951 77 and 1978 96 to study the interdecadal variations of this relationship a wet summer monsoon is preceded by a warm equatorial eastern pacific in the previous winter and followed by a cold equatorial eastern pacific in the following fall this relationship involves primarily the rainfall during the pre mei yu mei yu season may june but not the post mei yu season july august in a wet monsoon year the western north pacific subtropical ridge is stronger as a result of positive feedback that involves the anomalous hadley and walker circulations an atmospheric rossby wave response to the western pacific complementary cooling and the evaporation wind feedback this ridge extends farther to the west from the previous winter to the following fall resulting in an 850 hpa anomalous anticyclone near the southeast coast of china this anticyclone 1 blocks the pre mei yu and mei yu fronts from moving southward thereby extending the time that the fronts produce stationary rainfall 2 enhances the pressure gradient to its northwest resulting in a more intense front and 3 induces anomalous warming of the south china sea surface through increased downwelling which leads to a higher moisture supply to the rain area a positive feedback from the strong monsoon rainfall also appears to occur leading to an intensified anomalous anticyclone near the monsoon region this sst subtropical ridge monsoon rainfall relationship is observed in both the interannual timescale within each interdecadal period and in the interdecadal scale the sst anomalies sstas change sign in northern spring and resemble a tropospheric biennial oscillation tbo pattern during the first interdecadal period 1951 77 in the second interdecadal period 1978 96 the sign change occurs in northern fall and the tbo pattern in the equatorial eastern pacific sst is replaced by longer timescales this interdecadal variation of the monsoon sst relationship results from the interdecadal change of the background state of the coupled ocean atmosphere system this difference gives rise to the different degrees of importance of the feedback from the anomalous circulations near the monsoon region to the equatorial eastern pacific in a wet monsoon year the anomalous easterly winds south of the monsoon enhanced anomalous anticyclone start to propagate slowly eastward toward the eastern pacific in may and june apparently as a result of an atmosphere ocean coupled wave motion these anomalous easterlies carry with them a cooling effect on the ocean surface in 1951 77 this effect is insignificant as the equatorial eastern pacific sstas already change from warm to cold in northern spring probably as a result of negative feedback processes discussed in enso mechanisms in 1978 96 the equatorial eastern pacific has a warmer mean sst a stronger positive feedback between ssta and the walker circulation during a warm phase tends to keep the ssta warm until northern fall when the eastward propagating anomalous easterly winds reach the eastern pacific and reverse the ssta

a strengthened impact of november arctic oscillation on subsequent tropical pacific sea surface temperature variation since the late 1970s the connection between november arctic oscillation ao and the following spring summer tropical pacific sea surface temperature sst experienced a pronounced enhancement around the late 1970s the connection was weak before but strong after the late 1970s the present study investigates the plausible reasons for the connection change after the late 1970s significant anomalous cyclone appears over subtropical north pacific and pronounced anomalous westerly winds occur over tropical western pacific in the positive phase of november ao as such november ao could exert a significant influence on the subsequent spring summer tropical pacific sst variation by contrast before the late 1970s anomalous cyclone and associated anomalous westerly winds to its south are weak and shift northward thereby the connection between november ao and tropical pacific sst is weak further analyses suggest that the interdecadal change in the anomalous cyclone over the subtropical north pacific may be related to the change in the november ao s pacific component and the strength of feedback of synoptic scale eddy to mean flow specifically after the late 1970s november ao s pacific component displays a zonally elongated structure which is favorable for the formation of easterly wind anomalies over the mid latitude north pacific and related wave mean flow interaction in addition feedback of synoptic eddy to mean flow is enhanced after the late 1970s which is partly related to the intensification of the north pacific storm track this may also contribute to enhancement of the anomalous cyclone over the subtropical pacific

using a 2d shallow water model to assess large scale particle image velocimetry lspiv and structure from motion sfm techniques in a street scale urban drainage physical model abstract physically based numerical modelling of surface processes in urban drainage such as pollutant wash off or the assessment of flood risks requires appropriate calibration and terrain elevation data to properly simulate the overland flows and thus to achieve useful results accordingly this study aims to obtain an accurate representation of the runoff generated by three different rain intensities 30 50 and 80 mm h in a full scale urban drainage physical model of 36 m2 the study focuses firstly on applying the structure from motion sfm photogrammetric technique to carry out a high resolution and accurate topographic survey this topography was implemented in a 2d shallow water model and the results were compared with those obtained using traditional data point measured topography negligible differences were found when comparing the two models with measured discharges at the physical model gully pots however significant differences were obtained in the velocity distributions especially in the shallowest flow areas where drainage channels of a few millimeters depth appeared in the high resolution topographic survey results from the numerical model were compared with overland flow velocities determined by applying a modified large scale particle image velocimetry lspiv methodology using fluorescent particles with the sfm topography the 2d model was able to obtain a better representation of the experimental data since small scale irregularities of the pavement surface could be represented in the model domain at the same time lspiv was presented as a very suitable tool for the accurate measurement of runoff velocities in urban drainage models avoiding the interference of raindrop features in the recorded images and with overland water depths in the order of few millimeters

the different configurations of the east asian polar front jet and subtropical jet and the associated rainfall anomalies over eastern china in summer abstractto investigate the concurrent impacts of the east asian polar front jet eapj and subtropical jet easj on the summer rainfall over eastern china positive strengthened eapj with weakened easj and negative weakened eapj with strengthened easj configurations are identified in the positive configuration rainfall decreases in the northern part of eastern china and increases in the southern part vice versa in the negative configuration the possible mechanisms maintaining the two jet configurations are further proposed from the perspectives of sea surface temperature sst and synoptic scale transient eddy activities stea in the positive configuration meridional distributed cold warm sst anomalies over the eastern north pacific may induce regional circulation and meridional temperature gradient anomalies which can strengthen the eapj and weaken the easj the central pacific la nina like sst anomalies are related with the arctic vortexlike anomalies in the stratosphere which may strength

approach to saturation analysis of hysteresis measurements in rock magnetism and evidence for stress dominated magnetic anisotropy in young mid ocean ridge basalt abstract young mid ocean ridge basalts contain titanomagnetite crystals of varying size and composition many studies of their hysteresis properties have found m rs m s ratios considerably above the theoretical limit of 0 5 for uniaxial single domain particles since titanomagnetite is a cubic mineral high m rs m s could occur due to cubic anisotropy which allows for m rs m s values up to 0 866 on the other hand titanomagnetites with high ti content possess extremely large magnetostriction constants already slight internal stress easily outweighs cubic anisotropy and enforces uniaxial behavior are high m rs m s ratios now a proof for very low internal stress no on the contrary previous studies on synthetic titanomagnetite with high m rs m s show that after annealing this ratio decreases a possible explanation is that insufficient saturation of the hysteresis loop used to infer m rs m s leads to underestimation of m s here a systematic experimental study on a young mid ocean ridge basalt using fields of up to 7 t demonstrates that indeed the m rs m s ratio of the single domain fraction does not significantly deviate from the theoretical value of 0 5 for uniaxial anisotropy it is further estimated that internal stress above 200 mpa is necessary to explain the observed hysteresis behavior a value which is consistent with recent independent approximations on the other hand theoretical loops for cubic minerals do not fit the observed data in order to assess the validity of m s determinations from hysteresis measurements an improved method to evaluate the approach to saturation behavior of hysteresis loops is developed it allows to recognize insufficiently saturated loops and thereby helps to avoid misinterpretation of standard m rs m s measurements when high fields are not accessible

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

steady and non steady state magma chambers below the east pacific rise volcanic rocks collected on flowline traverses on the flanks of the east pacific rise epr document changes in axial magma chemistry with time providing a record of the thermal history of axial magma chambers amc we present data for a sample set of closely spaced 1 2 km samples along epr flowlines at three localities out to 800 ka showing both steady constant average temperature and non steady state behavior of magma chambers on time scales of 200 500 ka though based on only three symmetrical traverses so far it appears that magmatically robust ridge locations 11 20 n and 9 30 n have steady state chambers whereas a magmatically starved axis 10 30 n shows large temperature changes with time these observations provide a new petrologic perspective to the ongoing debate regarding the significance and causes of morphologic variations along the axis of the east pacific rise

holocene paleointensities thellier experiments on submarine basaltic glass from the east pacific rise a complete description of the geomagnetic field requires both paleodirectional and paleointensity data although the paleointensity data base has grown steadily over the last three decades it remains limited in time and space the majority of data are of holocene age and come from europe furthermore it has been difficult to assess the reliability of the paleointensity determinations here we present paleointensity determinations on precisely dated holocene 0 to 3500 years old submarine basaltic glass from the east pacific rise 15 s to 22 s although hysteresis measurements and low temperature isothermal remanent magnetization irm acquisition experiments document a significant contribution of superparamagnetic grains high blocking temperatures above 400 c and curie temperatures between 490 c and 550 c indicate a single domain low ti magnetite as the carrier of the remanent magnetization this notion is further supported by the fact that saturation of remanence is achieved in moderate fields of about 200 300 mt submarine basaltic glass proves to be nearly ideal for paleointensity determinations in that it produces a high success rate for thellier experiments twenty six out of 30 samples resulted in acceptable paleointenisty determinations multiple experiments on splits from the same sample show good reproducibility the paleointensities for zero age glasses correspond precisely with the present field intensity at the site of recovery the results of the remaining samples range from 16 7 to 53 9 t with corresponding virtual axial dipole moments vadm of 3 61 1022 to 11 9 1022 a m2 the intensities vary rapidly with time excluding a westward drifting nondipole component as the source for these fluctuations basaltic glass is frequently recovered in both dredged and drilled material from the ocean floor the availability of submarine basaltic glass throughout the world oceans therefore holds great potential for a better distribution of paleointensity data through time and space

reconstructing the western boundary variability of the western pacific subtropical high over the past 200 years via chinese cave oxygen isotope records cave oxygen isotope 18o records have been important in characterizing asian monsoon variations on a wide range of timescales the climatic significance of the 18o proxy of the cave records and its main control factors however remain hotly debated especially with respect to annual to decadal timescales in particular while the spatial and intensity variations of the western pacific subtropical high wpsh affects the east asian monsoon remarkably on annual to decadal timescales cave records up to present do not show clear evidence of the wpsh signal here we report a new high resolution average of 1 5 months 18o record from dongshiya cave qinling mountain central china the region is highly sensitive to variations in the position of the wpsh western boundary which in turn regulates the alternation of dominant moisture sources between the proximal pacific ocean and the remote indian ocean together with another cave record near the wpsh western boundary we established a new index to reconstruct variations of the wpsh western boundary over the past 200 years our new data revealed two significant periodicities 12 and 2 7 years respectively that can be causally linked to solar and enso variances correspondingly

thermomagnetic investigations of titanomagnetite in submarine basalts evidence for differential maghemitization abstract initial susceptibility k coercive force h c remanent coercive force h rc and saturation induced and remanent magnetizations j s and j rs have been measured at a series of 10 12 temperature steps between ambient temperature and 340 c for three selected fine or coarse grained submarine basalts ranging in age from the present to 30 ma possible magneto chemical changes which could have been induced by the successive heatings were checked through repeated measurements at room temperature which showed that no significant changes of the hysteresis parameters occurred below the 300 c temperature step average curie points are between 110 and 170 c but a quite large dispersion of curie points exists in a single rock sometimes over 400 c at room temperature the bulk of magnetic oxides consist either of multidomain md grains in the two coarse grained rocks dolerites or of small pseudosingle domain psd particles in the fine grained rock a pillow basalt the temperature dependence of coercivity of the oldest coarse grained rocks is surprisingly different from that of synthetic titanomagnetites coercivity is found to increase at intermediate temperatures with a maximum in the range 250 300 c in the most spectacular example h c rises from 28 to 75 oe and h rc from 67 to 200 oe when temperature rises from 20 to 235 c correlatively j rs j s increases to 0 3 indicating the presence of small psd grains the youngest pillow basalt sample displays similar although faint evidence of the presence of grains finer and with higher curie points than the bulk of the titanomagnetite population this thermal behaviour of submarine basalts is interpreted as the result of differential maghemitization within a single rock the finest grains being more rapidly and more completely oxidized at low temperature in our 3 ma old coarse grained sample the average oxidation index z is only 0 3 average curie point 110 c while the finest grains are completely maghemitized z 1 with a curie point of the order of 450 c

low temperature oxidation in morb of titanomagnetite to titanomaghemite a gradual process with implications for marine magnetic anomaly amplitudes mid ocean ridge basalt morb samples varying in age from recent to jurassic were selected for electron microscopic and rock magnetic studies our observations indicate that the degree of oxidation of titanomagnetite in morb increases only gradually with sample age the titanomagnetite in recent morb 100 ka both electron microscopic observations and rock magnetic data support the notion that low temperature oxidation of titanomagnetite to titanomaghemite in morb is a gradual process moreover the rate of maghemitization is controlled by many factors on both macroscopic and microscopic scales including regional oceanic crustal structures lithological features grain size and surrounding matrices pillow lavas and the tops of massive flows tend to have higher degrees of oxidation than the interiors of massive flows owing to higher porosity and permeability of the former in contrast interstitial glass can protect fine titanomagnetite grains from alteration the natural remanent magnetization nrm intensity of morb varies as a function of age magnetic granulometry concentration of magnetic materials and the degree of alteration fine grained morb samples typically have higher nrm intensity the nrm intensity appears to decrease substantially with increasing degree of maghemitization and hence with age the envelope of the smoothed magnetic anomaly amplitudes resembles the change in nrm intensity for morb samples of the last 30 million years but the underlying assumption that the highest degree of maghemitization observed in the samples of a given age is entirely responsible for these intensity changes is not supported maghemitization of the micrometer sized and larger grains is probably only partly responsible whereas a significant contribution to nrm intensities is inferred from those submicrometer sized titanomagnetite grains that remained protected from oxidation by the surrounding matrix of interstitial glass

global patterns of enso induced precipitation although there have been many analyses of el nino southern oscillation enso induced precipitation anomalies global patterns from these analyses remain incomplete here we combine recent satellite estimates of oceanic precipitation and historical rain gauge records to derive a global climatology of enso induced precipitation anomalies using empirical orthogonal function eof analyses the patterns suggest that the re arrangement of convection centers of the walker circulation during enso events induces large precipitation anomalies in the tropics while associated changes in the monsoon systems through the hadley cell over the pacific indian and atlantic oceans and their interactions with midlatitude westerlies generate coherent anomaly patterns over the extratropics our results can be used to evaluate climate models and forecast enso induced precipitation anomalies

partial anhysteretic remanent magnetization in magnetite 1 additivity 1 we have tested the additivity of partial anhysteretic remanent magnetization parm for suites of eight synthetic magnetites with mean grain sizes from 65 nm to 18 m and 18 natural samples including lake sediments oceanic and continental volcanic rocks gabbros and granites in both synthetic and natural sample suites domain states inferred from hysteresis and other magnetic properties vary from single domain sd through pseudosingle domain psd to multidomain md for each sample total arm intensity was compared with sums of partial arms of three different types four conjugate pairs of parallel parms four pairs of perpendicular parms and one set of five neighboring parallel parms in each case the intervals of alternating field af over which a steady field h was applied to produce the partial arms are nonoverlapping and cover the entire af range 0 100 mt used to produce the total arm additivity of partial arms was verified to better than 3 for all the samples whatever the domain state sd psd and md or composition ranging from pure magnetite to x 0 6 titanomagnetite the universality of parm additivity is unexpected because its analog partial thermoremanent magnetization ptrm deviates from ideal behavior as the grain size increases and the domain structure becomes md the different behaviors probably result from the fact that parm is produced at ordinary temperatures over short times whereas the most intense ptrm is produced at temperatures approaching the curie point with significant dwell times promoting such processes as isothermal remanence acquisition domain nucleation and domain wall reequilibration verification of the law of additivity of parms is an encouraging first step toward validating pseudo thellier and other methods of paleointensity determination that use arm in place of or in addition to trm

oceanic origin of the interannual and interdecadal variability of the summertime western pacific subtropical high 1 a recent study found that the western pacific subtropical high wpsh exhibits both quasi biennial 2 3 years and low frequency 3 5 years oscillations while the quasi biennial oscillation is prominent in 1990s the 3 5 year oscillation is dominant in 1980s the two oscillations were attributed to the atmospheric response to the remote forcing of sea surface temperature sst in the maritime continent and equatorial central eastern pacific respectively the present study confirms this hypothesis when forced by observational sst the ensemble simulation with the ncar cam2 model reasonably reproduces the main characteristics of quasi biennial oscillation and low frequency oscillations of the wpsh the quasi biennial oscillation is associated with anomalous overturning circulation characterized by enhanced convection over the maritime continent and subsidence over the western north pacific the low frequency oscillation is mainly modulated by remote forcing of ssta in the equatorial central eastern pacific the model reasonably reproduces the interdecadal transition of the wpsh from low frequency oscillation in 1980s to quasi biennial oscillation in 1990s suggesting that the sst forcing is an essential factor to modulate the interdecadal variation of the wpsh

magnetization of axial lavas from the southern east pacific rise 14 23 s geochemical controls on magnetic properties although the spatial association of iron rich lavas and high amplitude magnetic anomalies is well documented a causal link between enhanced iron content and high remanent magnetization has been difficult to establish here we report magnetic data from approximately 250 samples with 8 16 feo total iron as feo from the southern east pacific rise epr that provide strong support for the presumed geochemical dependence of remanent intensity the limited age range 0 6 ka of axial lavas from this ultrafast spreading ridge 150 mm yr full rate effectively minimizes variations resulting from time dependent changes in geomagnetic intensity or low temperature alteration systematic sampling relative to the chilled margin illustrates that substantial grain size related variations in magnetic properties occur on a centimeter scale both microprobe data and curie temperatures suggest that the average groundmass titanomagnetite composition in the southern epr samples is approximately constant modal modified ulv6spinel content 0 67 over a wide range of lava compositions saturation magnetization and saturation remanence are highly correlated with feo r 0 73 and 0 83 respectively indicating that more iron rich lavas have higher abundances of otherwise similar titanomagnetite we show that there is a good correlation between natural remanent magnetization nrm and feo provided that sufficient specimens are used to determine the average nrm of a sample r 0 63 because the range of iron contents in mid ocean ridge basalts is limited the best fit slope 4 44 a m per feo in an ambient field of 0 030 mt should provide reasonable bounds on the equatorial magnetization of submarine lavas 10 a m at 8 5 feo and 50 a m at 16 feo finally we demonstrate that along axis variations in nrm closely parallel geochemical changes along the southern epr where magnetization values deviate significantly from those predicted from the range of measured feo contents these discrepancies may reflect additional unrecognized geochemical variability

effect of summer arctic sea ice on the reverse august precipitation anomaly in eastern china between 1998 and 2016 abstractthe 1997 98 and 2015 16 el nino episodes are regarded as two super el nino events and have exerted profound influence on eastern china summer rainfall as expected however on the subseaso

decadal modulation of precipitation patterns over eastern china by sea surface temperature anomalies abstractannual precipitation anomalies over eastern china are characterized by a north south dipole pattern referred to as the southern flooding and northern drought pattern sf nd fluctuating on decadal time scales previous research has suggested possible links with oceanic forcing but the underlying physical mechanisms by which sea surface temperature sst variability impacts the dipole pattern remains unclear idealized atmospheric general circulation model experiments conducted by the u s clivar drought working group are used to investigate the role of historical sst anomalies associated with pacific el nino southern oscillation enso like and the atlantic multidecadal oscillation amo patterns in this dipole pattern the results show that the pacific sst pattern plays a dominant role in driving the decadal variability of this dipole pattern and the associated atmospheric circulation anomalies whereas the atlantic sst pattern contributes to a much lesser degree the direct atmospheric resp

low temperature magnetic behavior of titanomagnetites titanium substitution has a significant effect on the temperature dependence 5 300 k of low temperature saturation remanence and of initial susceptibility in synthetic and natural titanomagnetite fe3 xtixo4 0 x 0 4 and electronic and lattice relaxation phenomena over the entire titanomagnetite compositional range these features produce diagnostic magnetic behavior useful for titanomagnetite identification in natural samples moreover the apparent similarities between the thermal decay of low temperature remanence of titanomagnetite with pyrrhotite pure magnetite and superparamagnetic phases can lead to complications in interpreting low temperature remanence data when titanomagnetite is present

magnetic state of 10 40 ma old ocean basalts and its implications for natural remanent magnetization abstract the natural remanent magnetization nrm of ocean basalts giving rise to the pattern of marine magnetic anomalies is known to be of comparatively low intensity for about 20 ma old oceanic crust the aim of this study is to detect possible peculiarities in the rock magnetic properties of ocean basalts of this age and to establish a link between magnetomineralogy rock magnetic parameters and the low nrm intensity ocean basalts covering ages from 0 7 to 135 ma were selected for rock magnetic experiments and their room temperature hysteresis parameters curie temperature and temperature dependence of saturation magnetization ms t was determined and complemented by reflected light microscopy the majority of samples is magnetically dominated by titanomagnetite and titanomaghemite with increasing oxidation state with age for these a strong dependence of hysteresis parameters on the age of the samples is found the samples have a minimum in saturation magnetization and a maximum in magnetic stability in the age interval ranging from approximately 10 to 40 ma coinciding with the age interval of low nrm intensity the observed change in saturation magnetization is in the same order as that for the nrm intensity a further peculiarity of the titanomaghemites from this age interval is the shape of their ms t curves which display a maximum above room temperature neel p type and sometimes a self reversal of magnetization below room temperature neel n type these special rock magnetic properties can be explained by titanomagnetite low temperature oxidation and highly oxidized titanomaghemites in the age interval 10 40 ma a corresponding measurement of the nrm at elevated temperature allows to identify a maximum in nrm intensity above room temperature for the samples in that age interval this provides evidence that the nrm is equally carried by titanomaghemites and that the low nrm intensities for about 20 ma old ocean basalts are caused consequently by the low saturation magnetization of these titanomaghemites

a dynamic index for the westward ridge point variability of the western pacific subtropical high during summer abstractbased on the ridge line of the western pacific subtropical high wpsh and the theory of gradient wind approximation a dynamic index for the westward ridge point wrpi of the wpsh is defined owing to its definition the new dynamic index can be used to analyze the evolution of the wpsh at various time scales over most isobaric surfaces the wrpi comprises two dimensions labeled zwrpi and mwrpi which depict the zonal and meridional movement respectively of the westward ridge point of the wpsh the rationality and reliability of the dynamic index were validated using reanalysis atmospheric circulation outgoing longwave radiation surface air temperature and rainfall data the wrpi series revealed that the westward ridge point of the wpsh generally advances poleward while withdrawing eastward furthermore there were close relationships between the wrpi atmospheric circulation outgoing longwave radiation and precipitation over east asia and the western pacific in summer the significant co

rock magnetism of remagnetized paleozoic carbonates low temperature behavior and susceptibility characteristics we have conducted a new set of rock magnetic experiments on samples of remagnetized paleozoic carbonates of eastern north america these experiments were designed to investigate the origin of the unusual hysteresis behavior of these rocks by evaluating 1 the importance of ferrimagnetic pyrrhotite as a remanence carrier and 2 the sources of low field susceptibility low temperature measurements of saturation isothermal remanent magnetization sirm indicate that the pyrrhotite magnetic transition at 32 k is absent in the trenton and onondaga limestones of new york this transition is observed but poorly expressed in the knox group of east tennessee room temperature sirms cooled to 10 k in zero field lose a small fraction of their intensity between 30 and 35 k samples from all three formations show a broad peak in irm intensity at about 200 k which is typical of pyrrhotite in the trenton and onondaga samples the ferrimagnetic component of low field susceptibility is significantly larger than the ratio mrs hcr and is thus probably due dominantly to magnetite in some of the knox samples the reverse is true suggesting an important pyrrhotite contribution for all of the samples the ferrimagnetic susceptibility normalized by the saturation magnetization is anomalously high about a factor of 5 or 10 higher than the typical value for magnetite we believe that this indicates a very substantial contribution from superparamagnetic particles strong frequency dependence of susceptibility and very high ratios of anhysteretic to saturation remanence confirm the importance of ultrafine particles spanning the superparamagnetic single domain boundary all three of these chemically remagnetized carbonates units exhibit the following properties which have not previously been found together for any rock or synthetic analog and which therefore appear to constitute a diagnostic set of rockmagnetic criteria for recognizing chemically remagnetized rocks mrs ms 0 89 hcr hc 0 6 k ms 50 m a arm sirm 20 ka mrs hcr 50

an interdecadal change in southern china summer rainfall around 1992 93 the present study documents a pronounced interdecadal change in summer rainfall over southern china around 1992 93 and explores the plausible reasons for this change the summer rainfall is persistently below normal during 1980 92 and above normal during 1993 2002 coherent changes in atmospheric circulation are identified over east asia and the south china sea scs western north pacific wnp the increase in rainfall is accompanied by an increase in lower level convergence midtropospheric ascent and upperlevel divergence over southern china the changes in lower level winds feature two anomalous anticyclones one over the scs subtropical wnp and the other over north china mongolia the outflows from the two anomalous anticyclones converge over southern china leading to anomalous moisture convergence enhanced ascent and increased rainfall the development of the northern anticyclone is related to an increase in the tibetan plateau snow cover in the preceding winter spring that leads to a contrast in temperature change between the plateau and the surrounding regions the relatively small temperature change over the plateau coupled with increases in temperature to the west and the east leads to an increase in surface pressure extending northward from the plateau the development of the southern anticyclone is related to an increase in sea surface temperature in the equatorial indian ocean that enhances lower level convergence and ascent the accompanying upper level divergent flows from the tropical indian ocean to the scs wnp lead to the development of anomalous descent and lower level anomalous anticyclone over the scs wnp

variable ti content and grain size of titanomagnetite as a function of cooling rate in very young morb transmission electron microscopy observations and rock magnetic measurements on a pillow from the new flow extruded in 1993 at the juan de fuca ridge demonstrate that ti content in large up to 40 m titanomagnetite grains varies as a function of the cooling rate large grains in the interior of the pillow have a narrow composition range of approximately x 0 6 where x represents the ulvospinel content in the solid solution series with magnetite in contrast the titanomagnetite grains near the pillow rim are progressively smaller and have a broad composition range average x 0 45 within 0 5 cm of the rim a significant portion of the grains is single domain sd to superparamagnetic sp and appears to have little or no ti this lower ti content provides a ready explanation for the higher curie temperature near the glassy margin of the pillow moreover determination of the oxidation state of the titanomagnetite does not show low temperature oxidation anywhere within the pillow indicating no rapid alteration to titanomaghemite as previously suggested for this very young mid ocean ridge basalt morb in order to explain the curie temperatures submicrometer titanomagnetite in interstitial glass in the interior of the pillow also shows variable x values these grains make contributions to susceptibility that show up as high up to 580 c curie temperatures in thermomagnetic analyses and they appear to be sd to sp the variation of x values for the titanomagnetite in the morb is consistent with thermodynamic and kinetic considerations because crystallization of titanomagnetite in the morb is controlled by processes depending on cooling rate and crystal melt fractionation

variations in magnetization intensity and low temperature titanomagnetite oxidation of ocean floor basalts the remanent magnetization of the oceanic crust exhibits a systematic long term variation which correlates with the amplitudes of marine magnetic anomalies after a sharp initial decrease of natural remanent magnetization intensity a minimum is reached at 20myr followed by a gradual increase up to ages of 120 myr the progressive sea floor alteration of the magnetic minerals carrying the crustal magnetism is proposed as a cause for this behaviour

theory and application of the day plot mrs ms versus hcr hc 2 application to data for rocks sediments and soils 1 new theoretical curves relating the hysteresis parameters mrs ms and hcr hc for single domain sd superparamagnetic sp pseudo single domain psd and multidomain md grains and their mixtures are applied to published data for natural materials the day plot of mrs ms versus hcr hc has been used to crudely classify samples into box like sd psd and md or sometimes incorrectly md sp regions with arbitrary boundaries new type curves for md psd sd md and sd sp grains and mixtures permit more subtle and precise modeling the predicted md trend and its junction with the psd trend are observed in two data sets for magnetite spherules from carbonate rocks and for temperature varying hysteresis results spanning the verwey transition the latter data are the basis of a suggested new method for pinpointing the psd md threshold size selected data for pottery clays soils and paleosols generally follow sd md type curves and indicate intermediate size psd magnetite with narrow to broad size distributions a lake sediment section with known grain size progression tracks in the predicted sense along the sd md trend selected data for glaciomarine and pelagic sediments are also generally compatible with sd md trends examples of remagnetized carbonate rocks submarine basaltic glasses and glassy rims of pillow basalts all follow predicted sp sd or sp psd mixing curves with a large range in volume fraction of sp grains 0 75 but a narrow range of sp particle sizes 10 2 nm larger sp grains spanning the range to sd size 25 30 nm are absent for unknown reasons oceanic dolerites gabbros and serpentinized peridotites in some cases fall in a novel region of the day plot parallel to but below magnetite sd md mixing curves

interdecadal variability of summer climate over east asia and its association with 500 hpa height and global sea surface temperature interdecadal variability of summer climate rainfall and temperature in east asia china and japan and its association with the anomalies of geopotential heights at 500 hpa over the northern hemisphere nh global sea surface temperature ssta and outgoing longwave radiation olr were examined an abrupt change was found in the middle and by the end of the 1970s in the variations of time coefficients of the second mode of singular value decomposition svd2 for the summer rainfall and temperature in china the rainfall anomaly around 1977 1979 changes from above normal to below normal and the temperature changes from below normal to above normal in the southern and southwestern parts of china a similar interdecadal variability was also found in the summer climate variations in the southwest islands of japan the 500 hpa height anomalies related to the spatial pattern of svd2 shows a clear dipole pattern the negative center is located in mongolia and northeastern china and the positive center is located in middle and southern china the abrupt change of summer climate in the middle and by the end of the 1970s over the subtropical regions of east asia is characterized with the intensification and westward and southward extension of the western pacific subtropical high wpsh it is also observed in geopotential height variations over eurasia around 1977 1978 an abrupt change of sst over the tropical indian ocean and tropical western pacific was also found around 1976 1977 it is indicated that interdecadal variability of summer rainfall and temperature over east asia is largely influenced by the change of ssta and convective activity in the tropical indian ocean and tropical western pacific the convective activity over the tropical indian ocean and tropical western pacific is usually enhanced when the sst is warmer than normal so the subtropical high anomalies over the subtropical regions of east asia are intensified through the enhancement of a hadley cell as a result the subtropical regions of east asia including southern and southwestern china and the southwest islands of japan are covered by a positive height anomaly at 500 hpa where the temperature is above normal and the rainfall is below normal

source as a controlling factor on the quality and interpretation of sediment magnetic records from the northern north atlantic magnetic properties of eight particle size ranges from nine locations in iceland and 26 locations in southern greenland reveal the importance of source variation for our understanding of paleomagnetic and environmental magnetic records in the marine environment these terrestrial samples show varying degrees of particle size dependence with all samples showing that the silt fraction possesses greater concentrations of ferrimagnetic minerals than either clay or sand fine pseudo single domain psd size magnetic grains dominate the magnetic assemblage of all icelandic fractions in contrast greenlandic samples possess greater variation in magnetic grain size only fine silt and clay are as magnetically fine as the icelandic psd grains while greenlandic silts and sands are dominated by coarser psd and multi domain grains these observations from potential marine sediment sources suggest that the silt size fraction is a likely driver for much of the concentration dependent parameters derived from bulk magnetic records and that the magnetic grain size of the silt fraction can be used to discriminate between icelandic and greenlandic sources using these results to examine magnetic grain size records from marine sediment cores collected across the northern north atlantic suggests that source not just transport controlled physical grain size has a significant impact on determining the magnetic grain size at a particular location homogeneity of magnetic grain size in icelandic sediments at least partially explains the consistent quality of paleomagnetic records derived from cores surrounding iceland and their ability to buffer large environmental changes

wasp waisted hysteresis loops from a pyrrhotite and magnetite bearing remagnetized triassic limestone remagnetized samples of the triassic prezzo limestone from northern italy contain a mixture of pyrrhotite and magnetite as deduced by thermal unblocking characteristics of triaxial isothermal remanent magnetizations irm s and low temperature cycling of saturation irm s hysteresis loops are commonly wasp waisted and remanent coercivity curves contain a break in slope as a result of the contrast in coercivity between remanence carrying pyrrhotite and magnetite the relative proportion of the high to low remanent coercivity fractions as deduced by the study of the remanent coercivity curves seems to control the degree of wasp waistedness of the hysteresis loops samples that are dominated by one of the two coercivity end members have lower bcr bc values as well as hysteresis loops that have a less pronounced constricted waist compared to samples with higher bcr bc values maximum bcr bc values and thus maximum degrees of wasp waistedness in the hysteresis loops are attained when the low remanent coercivity fraction contributes 15 35 to the bulk remanent coercivity curves

experimental validation of a 2d overland flow model using high resolution water depth and velocity data summary this paper presents a validation of a two dimensional overland flow model using empirical laboratory data unlike previous publications in which model performance is evaluated as the ability to predict an outlet hydrograph we use high resolution 2d water depth and velocity data to analyze to what degree the model is able to reproduce the spatial distribution of these variables several overland flow conditions over two impervious surfaces of the order of one square meter with different micro and macro roughness characteristics are studied the first surface is a simplified representation of a sinusoidal terrain with three crests and furrows while the second one is a mould of a real agricultural seedbed terrain we analyze four different bed friction parameterizations and we show that the performance of formulations which consider the transition between laminar smooth turbulent and rough turbulent flow do not improve the results obtained with manning or keulegan formulas for rough turbulent flow the simulations performed show that using keulegan formula with a physically based definition of the bed roughness coefficient a two dimensional shallow water model is able to reproduce satisfactorily the flow hydrodynamics it is shown that even if the resolution of the topography data and numerical mesh are high enough to include all the small scale features of the bed surface the roughness coefficient must account for the macro roughness characteristics of the terrain in order to correctly reproduce the flow hydrodynamics

spring arctic oscillation east asian summer monsoon connection through circulation changes over the western north pacific in the present study the links between spring arctic oscillation ao and east asian summer monsoon easm was investigated with focus on the importance of the north pacific atmospheric circulation and sea surface temperature sst to reduce the statistical uncertainty we analyzed high pass filtered data with the inter annual time scales and excluded the el nino southern oscillation signals in the climate fields using a linear fitting method the significant relationship between spring ao and easm are supported by the changes of multi monsoon components including monsoon indices precipitation and three dimensional atmospheric circulations following a stronger positive spring ao an anomalous cyclonic circulation at 850 hpa appears in southeastern asia and the western north pacific in summer with the easterly anomalies spanning from the pacific to asian continent along 25 n 30 n and the westerly anomalies south of 15 n at the same time the summer western north pacific subtropical high becomes weaker consistently the positive precipitation anomalies are developed over a broad region south of 30 n stretching from southern china to the western pacific and the negative precipitation anomalies appear in the lower valley of the yangtze river and southern japan the anomalous cyclone in the western north pacific persisting from spring to summer plays a key role in modulating easm and monsoon precipitation by a positive air sea feedback mechanism during spring the ao associated atmospheric circulation change produces warmer ssts between 150 e 180 near the equator the anomalous sensible and latent heating in turn intensifies the cyclone through a gill type response of the atmosphere through this positive feedback the tropical atmosphere and sst patterns sustain their strength from spring to summer that consequently modifies the monsoon trough and the western north pacific subtropical high and eventually the easm precipitation moreover the sst response to ao circulation is supported by the numerical simulations of an ocean model and the anomalous atmospheric circulation over the western north pacific is also reproduced by the dedicated numerical simulations using the coupled atmosphere ocean model the observation evidence and numerical simulations suggest the spring ao can impact the easm via triggering tropical air sea feedback over the western north pacific

magnetic alteration of zero age oceanic basalt the youngest sampled submarine lava flow which erupted june 1993 on the juan de fuca ridge provides the basis for a tight constraint on the initial or zero age magnetization state of morb detailed profiles of magnetic hysteresis parameters curie temperatures and unblocking temperatures of nrm with respect to the chilled margin of a pillow fragment show evidence of significant oxidation which preferentially affected the finest grain size fraction and principal remanence carrier of the titanomagnetite magnetic mineralogy the oxidation must have occurred during or immediately after initial cooling implying that morb is already appreciably magnetically altered before aging nevertheless successful results of thellier paleointensity experiments on the basalt sample lend support to the idea that crustal magnetization represented by morb preserves a record of geomagnetic intensity variations that may be reflected in small scale magnetic anomalies

characteristics of magnetite in submarine basaltic glass summary we have compared the rock magnetic characteristics of cretaceous submarine basaltic glass sbg from dsdp odp holes 417d 418a 807c and 543a to data from holocene glasses from the east pacific rise both groups are very similar in that they contain single domain low ti magnetite as the carrier of a strong and stable remanent magnetization the behaviour of magnetic hysteresis in sbg is however dominated by superparamagnetic grain size populations transmission electron microscopy revealed spherically shaped grains of 10 20 nm diameter with crystal lattice properties consistent with magnetite these grains could be responsible for the magnetic behaviour of sbg

interannual variability of eastern china summer rainfall the origins of the meridional triple and dipole modes the eastern china summer rainfall ecsr has a strong interannual variability and the leading mode of interannual ecsr variability is characterized by either meridional triple or dipole structures as claimed by previous studies in this study decadal differences of the leading ecsr modes are investigated using observational data and long term integrations of climate models observational analyses show that the leading mode of ecsr is characterized by a meridional triple structure during 1979 1993 whereas a meridional dipole structure during 1994 2014 in the 200 year air sea coupled simulation of community climate system model version 4 ccsm4 the leading mode of ecsr is characterized by triple structure in some decades whereas dipole structure in other decades and decadal shifts between the triple and dipole structures are seen in the 200 year simulation of the stand alone atmospheric component of ccsm4 i e cam4 forced by fixed sst annual cycle the triple mode and dipole mode are also identified suggesting both of these two modes and their decadal shift can be generated by atmospheric internal dynamics without air sea interaction as agreed by observation ccsm4 and cam4 simulations the positive negative phase of the triple leading mode is associated with enhanced weakened western north pacific subtropical high southward northward shifted east asian jet and meridional wave train along the east asian coast the positive negative phase of the dipole leading mode is associated with enhanced weakened western north pacific subtropical high enhanced weakened east asian jet and zonal wave train over mid latitude eurasian continent

grain size dependent magnetic discrimination of iceland and south greenland terrestrial sediments in the northern north atlantic sediment record abstract we use isothermal and temperature dependent in field and magnetic remanence methods together with electron microscopy to characterize different sieved size fractions from terrestrial sediments collected in iceland and southern greenland the magnetic fraction of greenland silts 3 63 m and sands 63 m is primarily composed of near stoichiometric magnetite that may be oxidized in the finer clay

winter precipitation variability over korean peninsula associated with enso in this study winter precipitation variability associated with the el nino southern oscillation enso over the korean peninsula was investigated using a 5 pentad running mean data because significant correlation pattern cannot be revealed using seasonal mean data it was found a considerably significant positive correlation between nino3 sea surface temperature and precipitation during early winter from mid november to early december when the correlation coefficient is close to 0 8 in early december the correlation is distinctively weakened during late winter it is demonstrated that such sudden intraseasonal change in relation to enso is associated with the presence of anticyclonic flow over the kuroshio extension region kuroshio anticyclone in early winter there is strong southerly wind over the korean peninsula which is induced by the philippine sea anticyclone and kuroshio anticyclone however in january although the philippine sea anticyclone develops further the kuroshio anticyclone suddenly disappears as a result the impact of enso is considerably weakened over the korean peninsula these results indicate that the kuroshio anticyclone during el nino peak phase plays a critical role by strongly affecting northeast asia climate including the korean peninsula in addition it is also found that there are distinctive interdecadal changes of the relationship between enso and precipitation over the korean peninsula in particular the strong correlation in early winter is clearer in the recent 30 years than that in the previous period of 1950 1979

interdecadal change in the relationship between enso and the intraseasonal oscillation in east asia abstract the northward propagating intraseasonal oscillation npiso during the boreal summer is closely linked to the onset retreat and intensity of the east asian summer monsoon easm in this study interdecadal variability in the relationships between the npiso and el nino southern oscillation enso was investigated using long term outgoing longwave radiation data obtained from the 40 yr ecmwf re analysis era 40 for a 44 yr period 1958 to 2001 it was found that before the late 1970s the preceding winter enso influenced the early summer i e may to june npiso activity whereas after the late 1970s a strong relationship appeared during the later summertime i e july to august the may june npiso before the late 1970s was modulated by springtime indian ocean sea surface temperature warming and central north pacific suppressed convection anomalies and was consequently related to the enso induced west pacific wp pattern which shows a north south dipole structure over the north pacific from

relationship between enso and northward propagating intraseasonal oscillation in the east asian summer monsoon system 1 observational studies are presented on the relationship between el nino southern oscillation enso and the northward propagating intraseasonal oscillation npiso in the east asian summer monsoon easm system the summer npiso activity shows a significant correlation with the preceding winter extreme phase of enso cycles a higher correlation appears during late summer which is consistent with frequent heavy rainfall events at that time as revealed in some previous case studies the westward expansion of broad anticyclonic circulation over the western north pacific and the smaller cyclonic circulation around korea and japan are found to be associated with the npiso activity enso affects the late summer npiso activity through an atmospheric bridge and wave propagation the springtime indian ocean sea surface temperature warming induced by enso through the walker circulation leads to the downward motion and suppressed convection over the philippine sea and this generates the forced rossby wave train forming the above south to north low level circulation anomalies

how east asian westerly jet s meridional position affects the summer rainfall in yangtze huaihe river valley existing studies show that the change in the meridional position of east asian westerly jet eawj is associated with rainfall anomalies in yangtze huaihe river valley yhrv in summer however the dynamic mechanism has not been resolved yet the present study reveals underlying mechanisms for this impact for early summer and midsummer separately mechanism1 associated with eawj s anomalously southward displacement the 500 hpa westerly wind over yhrv is strengthened through midtropospheric horizontal circulation anomalies the westerly anomalies are related to the formation of warm advection anomalies over yhrv which cause increased rainfall through adiabatic ascent motion and convective activities the major difference in these processes between early summer and midsummer is the midtropospheric circulation anomaly pattern mechanism 2 associated with eawj s anomalously southward displacement the large day to day variability of midtropospheric temperature advection in midlatitudes is displaced southward by the jet s trapping transient eddies this change enhances the day to day variability of temperature advection over yhrv which in turn causes the increased rainfall in most part of yhrv through lower bound effect rainfall amount can not become negative there is not much difference in these processes between early summer and midsummer

interannual relationships between the tropical sea surface temperature and summertime subtropical anticyclone over the western north pacific 1 the interannual variability of the western north pacific subtropical high wnpsh in boreal summer is investigated with the use of the ncep ncar reanalysis data the most significant change of the 500 hpa geopotential height field appears at the western edge of the wnpsh with dominant 2 3 year and 3 5 year power spectrum peaks the 2 3 year oscillation of the wnpsh and associated circulation and sea surface temperature sst patterns possess a coherent eastward propagating feature with a warm sst anomaly ssta and anomalous ascending motion migrating from the tropical indian ocean in the preceding autumn to the maritime continent in the concurrent summer of a strong wnpsh a strong wnpsh is characterized by anomalous anticyclonic circulation and maximum subsidence in the western north pacific wnp the anomalous wnpsh circulation has an equivalent barotropic vertical structure and resides in the sinking branch of the local hadley circulation triggered by enhanced convection over the maritime continent a heat budget analysis reveals that the wnpsh is maintained by radiative cooling the 3 5 year oscillation of the wnpsh exhibits a quasi stationary feature with a warm ssta anomalous ascending motion located in the equatorial central eastern pacific and indian ocean and a cold ssta anomalous descending motion located in the western pacific the anomaly pattern persists from the preceding winter to the concurrent summer of a high wnpsh the greatest descent is located to the southeast of the anomalous anticyclone center where a baroclinic vertical structure is identified the zonal phase difference and the baroclinic vertical structure suggest that the anomalous anticyclone on this timescale is a rossby wave response to a negative latent heating associated with the persistent local cold ssta echam4 model experiments further confirm that the 2 3 year mode is driven by the ssta forcing over the maritime continent while the 3 5 year mode is driven by the local ssta in the wnp

dynamical and boundary forcing characteristics of regional components of the asian summer monsoon abstract in this paper the authors present a description of the internal dynamics and boundary forcing characteristics of two major subcomponents of the asian summer monsoon asm that is the south asian monsoon sam and the east southeast asian monsoon eam the description is based on a new monsoon climate paradigm in which the variability of asm is considered as the outcome of the interplay of a fast and an intermediate monsoon subsystem under the influence of slow external forcings two sets of regional monsoon indices derived from dynamically consistent rainfall and wind data are used in this study results show that the internal dynamics of sam are representative of a classical monsoon system in which the anomalous circulation is governed by rossby wave dynamics where anomalous vorticity induced by an off equatorial heat source is balanced by the advection of planetary vorticity on the other hand the internal dynamics of eam are characterized by a hybrid monsoon system featuring m

a statistical and dynamical characterization of large scale circulation patterns associated with summer extreme precipitation over the middle reaches of yangtze river the large scale circulation associated with extreme precipitation over the middle reaches of yangtze river mryr in early summer june and july are classified into three canonical patterns via hierarchical clustering the clustering results reveal a clear connection between the mryr extreme precipitation and anomalous moisture convergence over this region with the eastward expansion of south asia high and intensified westerly jets providing additional forcing for local rising motion in all three clusters the anomalous moisture convergence results from anomalous low level southwesterlies encountering anomalous northerlies from mid high latitudes the southwesterly anomaly is associated with the expansion of the western pacific subtropical high wpsh however the anomalous northerlies weakening the northward advance of the mei yu front are mainly driven by different extratropical circulation anomalies in the three clusters these anomalies range from zonally elongated barotropic disturbances to developing baroclinic disturbances that are potentially tied to upstream storm tracks all three clusters are characterized by a meridional dipole in geopotential height anomaly over the tropical subtropical east asia the northern and also more pronounced node of the dipole is located over the mryr with a cyclonic anti cyclonic height anomaly in the lower upper troposphere suggesting the critical role played by anomalous latent heating of extreme mryr rainfall in driving the formation of this dipole this dipole anomaly projects effectively onto the negative phase of the pacific japan teleconnection pattern and acts partly as a positive feedback to the westward expansion of the wpsh also discussed are the implications of the identified large scale circulation patterns for model evaluation and operational forecasting of extreme precipitation events

on the use of magnetic transient hysteresis in paleomagnetism for granulometry 1 parameters derived from magnetic hysteresis experiments have been used as granulometric indicators in paleomagnetism in practice discriminating the superparamagnetic sp fraction from the coarse grain magnetites in parameter ratio plots is often inconclusive to overcome this ambiguity transient hysteresis th has been recently proposed we have carried out micromagnetic simulations to provide a fundamental rationale for the use of th for granulometry we found that magnetic th results from the difference of magnetization configuration between ascending and descending hysteresis loops as a result of self demagnetization the descending branch has a tendency to keep a more uniform e g flower like configuration while the ascending branch prefers a less uniform e g vortex like structure according to our simulations th increases as the grain size increases and as the aspect ratio decreases we also carried out th measurements for well defined synthetic and natural samples it is notable that th from the simulation for samples with aspect ratio q 1 5 agrees well with the experimental observations for annealed magnetites of smaller sizes in general small th is a clear indication for the absence of complex magnetized structures adding th analysis to the hysteresis loop measurements requires a minor effort yet provides strong constraint on grain size

alteration and dissolution of fine grained magnetite and its effects on magnetization of the ocean floor abstract scanning and transmission electron microscopy stem of ocean floor pillow basalts with ages between 0 and 70 ma reveals progressive alteration of submicrometer titanomagnetite to phases such as goethite and clays in contrast larger titanomagnetite grains 1 m oxidize to titanomaghemite without apparent change in crystal morphology rock magnetic experiments are consistent with a selective removal of the submicrometer grains as the basalts age and show good correlations between the ranges of grain sizes observed by stem and those indicated by hysteresis properties remanence contributions from the larger pseudo single domain and multi domain titanium iron oxides are inferred to decrease only slightly as the ocean floor becomes older whereas the overall remanence decays with age as the substantial contribution from stable single domain titanomagnetite grains diminishes greatly due to their alteration to other phases although more work on many more samples is required to verify our conclusions the current data imply that this alteration is one of the reasons that amplitudes of marine magnetic anomalies diminish with age over time scales of tens of millions of years

some additional parameters to estimate domain state from isothermal magnetization measurements abstract domain state and mixing analysis based on isothermal magnetization measurements is often restricted to the use of the day plot in order to make more information from simple rock magnetic measurements accessible for the quantitative analysis of domain state four additional parameters are proposed two of them a hysteresis shape parameter and a coercivity ratio can be directly calculated from standard measurements of the hysteresis loop and backfield curve the other two a transient energy dissipation ratio and the viscosity of isothermal remanent magnetization require additional measurements which however do not increase measurement time noticeably the theoretical background of the above parameters is discussed their ability to discern domain state is shown for a small set of synthetic magnetite and titanomagnetite samples and in a case study of a transect from the rim to the center of a dredged mid ocean ridge basalt

the hysteresis properties of multidomain magnetite and titanomagnetite titanomaghemite in mid ocean ridge basalts abstract hysteresis measurements have been carried out on a suite of ocean floor basalts with ages ranging from quaternary to cretaceous approximately linear yet separate relationships between coercivity bc and the ratio of saturation remanence saturation magnetization mrs ms are observed for massive doleritic basalts with low ti magnetite and for pillow basalts with multi domain titanomagnetites with x 0 6 even when the morb has undergone low temperature oxidation resulting in titanomaghemite the parameters are still distinguishable although offset from the trend for unoxidized multidomain titanomagnetite the parameters for these iron oxides with different titanium content reveal contrasting trends that can be explained by the different saturation magnetizations of the mineral types this plot provides a previously underutilized and non destructive method to detect the presence of low titanium magnetite in igneous rocks notably morb

geomagnetic field intensity determination from pleistocene trachytic lava flows in jeju geopark 1 a composite of 28 trachytic lava flows were recovered from the jeju geopark drilling project jgdp in jeju geopark one of the new seven wonders of nature declared by unesco in 2011 each trachytic lava flow has a tendency to increase in magnetic grain size from the rapidly cooled brecciated margin and vesicle streaked zone downward into the massive crystalline flow interiors the brecciated margin and vesicle streaked zone of individual trachytic lava flow contains exclusively fine grained magnetite as inclusions in plagioclase high fidelity paleointensity determinations were obtained from 26 out of 224 examined samples from jgdp cores temporal variation of virtual axial dipole moments vadms calculated from the absolute paleointensity estimates follows the trend of sint 800 data for the interval from 80 to 360 ka high vadm from flow 21 possibly represents real intensity peak as previously recognized high vadm in japan at 336 ka in trans mexican volcanism 339 and in hawaii 340 350 ka perhaps such a strong magnetic intensity near 325 350 ka might be smoothed out in relative paleointensity records

on the characteristics of velocities fields in the vicinity of manhole inlet grates during flood events the accurate characterisation of flow from urban surfaces to sewer stormwater systems is important for urban drainage design and flood modelling risk identification however the geometrical complexity and large variety of drainage structures linking elements available makes model calibration and verification difficult in this study an extensive comparison between experimentally measured and numerically modelled flow characteristics in the vicinity of ten different designs of manhole grate was performed under drainage flow in sub critical conditions using a 2d surface piv spiv system the work presents the first detailed characterisation of velocity fields around these linking elements in addition it provides the first detailed verification of the ability of a 2d numerical model to describe both velocity fields and drainage flows the overall comparison shows a close relationship between numerical and the experimental results with some higher inflows in the experimental results as a consequence of a localised transition from weir to orifice condition near the void areas of the grates it was also noted that velocity differences decreased further from the manhole due mainly to the more directional flow overall the work demonstrates the potential for further use of 2d numerical models to describe flow conditions at linking elements either directly within modelling simulations or indirectly via the characterisation of energy loss coefficients

detecting uniaxial single domain grains with a modified irm technique summary mid ocean ridge basalt morb specimens have often been found to have high ratios of saturation remanence to saturation magnetization mrs ms this has been attributed either to dominant cubic anisotropy or to insufficient saturating field leading to overestimation of mrs ms of a dominantly uniaxial single domain usd assemblage to resolve this debate we develop an independent technique to detect usd assemblages the experimental protocol involves subjecting the specimen to bidirectional impulse fields at each step the experiment is similar to the conventional isothermal remanent magnetization irm acquisition experiment but the field is applied twice in antiparallel directions we define a new parameter irat as the ratio of the remanences at each field step and show it to have characteristic behaviour for the two assemblages irat 1 at all field steps for usd and 1 with a strong field dependence for multi axial single domain msd grains we verified the theoretical predictions experimentally with representative usd and msd specimens experiments with morbs gave low irats for specimens having high mrs ms this argues for a dominant msd assemblage in the morbs possibly cubic in nature although undersaturation of the samples can indeed be a contributing factor to the exceptionally high mrs ms this study shows that the nature of the assemblage cannot be dominantly usd