intensity of the geomagnetic field in western europe over the past 2000 years new data from ancient french pottery 1 we studied 14 groups of french pottery fragments dated between the 4th and 16th centuries the potsherds were analyzed using the thellier and thellier 1959 method revised by coe 1967 intensity values were corrected for thermoremanent magnetization trm anisotropy and cooling rate dependence of trm acquisition we first analyzed modern ceramics produced following ancient techniques and fired in a wood burning kiln inside of which field intensity was measured the recovered mean intensity is within 3 of the expected value which proves the reliability of our experimental procedure thermal experiments carried out at rapid and slow cooling rates clearly indicate that the cooling rate correction is critical in archeointensity studies our data indicate that large variations in intensity occurred in france over the last 2000 years two relative maxima in intensity are observed one between the 8th and 10th centuries and the second between the 14th and 15th centuries similarities are observed between the archeointensity data from france and ukraine yielding some evidence for eastward drift of geomagnetic sources between western and eastern europe from a d 800 to a d 1700 we also show that the dipole moment evolution proposed by mcelhinny and senanayake 1982 and yang et al 2000 for the last two millennia is likely biased toward higher values mainly because of the absence of correction for the cooling rate dependence of trm acquisition in most published archeointensity studies we finally underline a possible relationship valid at least in western europe between changes in direction and intensity of the geomagnetic field

decadal precipitation variability over europe and its relation with surface atmospheric circulation and sea surface temperature the relationships between decadal 5 year period observed winter precipitation pp variability over europe and atmospheric circulation and sea surface temperature sst during the period 1950 1995 are investigated more than 48 of the decadal precipitation variability is described by two modes a meridional dipolar pattern high pp over northern europe and low over southern europe the mediterranean and most of central europe explaining about 32 of the variance and an alternating pattern in latitude over europe high in central europe and low in far north western europe and the mediterranean explaining about 16 of the variance the first mode is strongly related to the north atlantic oscillation a canonical correlation analysis between regional precipitation and sea level pressure fields shows that a pp pattern similar to the first decadal pp mode is associated with a north westerly circulation anomaly pattern while a pp pattern similar to the second decadal pp mode is associated with a monopolar circulation anomaly pattern over most parts of europe the correlation map between the time series of expansion coefficients of the first pp mode and sea surface temperature emphasizes a global pattern which resembles the linear trend coefficients pattern of sst for the analysed period the second pp mode is associated with an sst anomaly pattern similar to that of the sst anomalies characterizing decadal el ni o southern oscillation sst pattern composite maps of global 500 mb geopotential height based on the time series of expansion coefficients of pp modes emphasize global patterns compatible with sst patterns after removing the linear trend from the data the first pp pattern remains almost unchanged but it emphasizes mainly regional connections the second spatial pattern of the second pp mode and its connections are not affected significantly by removing the trend

two thousand years of archeointensity from west africa this study presents 17 archeointensity estimates from senegal and mali two neighboring countries in west africa for the period 1000 bce to 1000 ce the archeological artifacts used in this study were collected during the course of two separate projects together spanning 22 years and across 8 separate excavations a primary objective of this study was to get accurate dates hence only samples with independent age constraints from pottery style detailed stratigraphy and 14c dates were used a total of 236 specimens from 63 samples were subjected to a double heating paleointensity experiment izzi method from which 95 specimens were selected using a set of very strict selection criteria the paleointensity results were corrected for differential cooling rate effects and remanence anisotropy additionally we demonstrate the equivalence of using tensors derived from anhysteretic and thermal remanences for correcting remanent anisotropy of the specimens and use the former for the anisotropy correction our data show good agreement with the most recent paleosecular variation model but are lower than the pre existing data which are mostly from egypt and morocco the presence of substantial non axial dipolar contributions in the region is evident when virtual axial dipole moments vadms from the published literature are calculated for 20 latitudinal bands and compared with our data the average vadm values show a distinct latitudinal gradient a prominent feature of this dataset is an intensity high observed prior to 700 ce in both senegal and mali comparing this peak with existing records from regions further to the north suggests a small but significant temporal offset and is interpreted to be additional evidence for a geomagnetic field with a significant and rapidly changing non axial dipolar contribution

geomagnetic field for 0 3 ka 2 a new series of time varying global models 1 steadily increasing numbers of archeomagnetic and paleomagnetic data for the holocene have allowed development of temporally continuous global spherical harmonic models of the geomagnetic field extending present and historical global descriptions of magnetic field evolution the current work uses various subsets of improved data compilations details of which are given in a companion paper by donadini et al 2009 and minor modifications of standard modeling strategies using temporally and spatially regularized inversion of the data and cubic spline parameterizations for temporal variations to produce five models with enhanced spatial and temporal resolution for 0 3 ka spurious end effects present in earlier models are eliminated by enforcing large scale agreement with the gufm1 historical model for 1650 1990 a d and by extending the model range to accommodate data older than 3 ka age errors are not considered as a contribution to data uncertainties but are included along with data uncertainties in an investigation of statistical uncertainty estimates for the models using parametric bootstrap resampling techniques we find common features but also significant differences among the various models indicating intrinsic uncertainties in global models based on the currently available holocene data model cals3k 3 based on all available archeomagnetic and sediment data without a priori quality selection currently constitutes the best global representation of the past field the new models have slightly higher dipole moments than our previous models virtual axial dipole moments vadms calculated directly from the data are in good agreement with all corresponding model predictions of vadms these are always higher than the spherical harmonic dipole moment indicating the limitations of using vadms as a measure of geomagnetic dipole moments

non dipole and regional effects on the geomagnetic dipole moment estimation the study of the temporal evolution of the dipole moment variations is a forefront research topic in earth sciences it constrains geodynamo simulations and is used to correct cosmogenic isotope production which is evidence of past solar activity and it is used to study possible correlations between the geomagnetic field and the climate in this work we have analysed the main error sources in the geomagnetic dipole moment computation from palaeomagnetic data the influence of the non dipole terms in the average approach the inhomogeneous distribution of the current palaeomagnetic database and the averaging procedure used to obtain the evolution of the dipole moment to evaluate and quantify these effects we have used synthetic data from a global model based on instrumental and satellite data the international geomagnetic reference field 11th generation results indicate that the non dipole terms contribute on a global scale of 6 in the averaged dipole moment whereas the regional non dipole contribution can show deviations of up to 35 in some regions such as oceania and different temporal trends with respect to the global dipole moment evolution in other ones such as europe and asia a regional weighting scheme seems the best option to mitigate these effects in the dipole moment average approach but when directional and intensity palaeomagnetic information is available on a global scale and in spite of the inhomogeneity of the database global modelling presents more reliable values of the geomagnetic dipole moment

pluton emplacement processes and tectonic setting of the 1 42 ga signal batholith sw usa important role of crustal anisotropy during regional shortening abstract plutons in the 1 42 ga signal batholith provide an important case study for understanding the regional tectonic setting of mesoproterozoic magmatism in the south western united states and processes of emplacement for plutons far from active plate margins mesoproterozoic plutons in the signal batholith were emplaced at 3 kbar and have a well developed magmatic fabric which is subparallel to variably oriented paleoproterozoic country rock foliations and shear zones indicating that pluton emplacement was strongly influenced by crustal anisotropy solid state deformation of mesoproterozoic granites is best developed in shallowly dipping roof domains 40 60 whereas in steep to vertical fabric domains granites are generally undeformed and locally cross cut older fabrics this suggests that roof domains remained hotter and experienced greater thermal softening and subsequent deformation structural and kinematic study of three separate plutons in the signal batholith indicate that pluton emplacement occurred in a regional contractional strain field although local complexities suggest possible stress field modification by pluton related stresses evidence to support regional contractional strain during emplacement includes 1 consistent dyke orientations throughout the batholith indicating a nne extension and se nw shortening 2 magmatic to solid state fabric transition in thrust sense deformation along the 40 60 dipping south east margin of the signal granite including melt filled shear zones and asymmetric k feldspar porphyroclasts and 3 syn tectonic textures in contact metamorphic andalusite prophyroblasts regional variation in shortening direction from se nw to n s during batholith emplacement may be related to pluton emplacement stresses locally dominating over the relatively low deviatoric stresses of regional deformation the main controlling factor for the geometry of pluton emplacement in the signal batholith was paleoproterozoic foliations and shear zones which provided conduits for movement of magma into the middle crust the flow of magma parallel to older structures may have been accommodated by a reduction in effective normal stresses by magma pressure and separation along the structural anisotropies this model for anisotropy influenced emplacement during weak regional contraction may be applicable to other 1 4 ga plutons across sw laurentia

geomagnetic intensity spike recorded in high resolution slag deposit in southern jordan article i nfo in paleomagnetism periods of high field intensity have been largely ignored in favor of the more spectacular directional changes associated with low field intensity periods of excursions and reversals hence questions such as how strong the field can get and how fast changes occur are still open in this paper we report on data obtained from an archaeometallurgical excavation in the middle east designed specifically for archaeomagnetic sampling we measured 342 specimens from 72 samples collected from a 6 1 m mound of well stratified copper production debris at the early iron age 12th 9th centuries bce site of khirbat en nahas in southern jordan seventeen samples spanning 200 yr yielded excellent archaeointensity results that demonstrate rapid changes in field intensity in a period of overall high field values the results display a remarkable spike in field strength with sample mean values of over 120 t compared to the current field strength of 44 t a suite of 13 radiocarbon dates intimately associated with our samples tight control of sample location and relative stratigraphy provide tight constraints on the rate and magnitude of changes in archaeomagnetic field intensities

proterozoic history and crustal evolution in southwestern colorado insight from u pb and sm nd data abstract new u pb age constraints and sm nd isotope data further establish the timing of magmatic and tectonic events from 1 8 to 1 4 ga in southwestern colorado and give insight into the interaction of crust and mantle systems during the assembly and evolution of orogenic belts along the southern margin of laurentia proterozoic orogenic events in the needle mountains led to crustal assembly thickening and tectonic reworking that was punctuated by periods of relative crustal stability pre 1 75 ga arc successions in southwestern colorado were produced and assembled into juvenile crust in an orogenic period that culminated in regional deformation and metamorphism that accompanied intrusion of synorogenic plutonic rocks from 1 73 to 1 71 ga emplacement of post orogenic plutonic rocks at 1 70 ga was followed by uplift and erosion and the deposition and deformation of siliciclastic sedimentary sequences paleoproterozoic crust underwent local melting and thermal metamorphism during invasion of felsic to mafic magmas at 1 43 ga that coincided with a pulse of intracratonic deformation invasion and melting of first cycle 1 8 1 7 ga crust at 1 71 and 1 43 ga involved heat and volatiles from mantle melts that were a catalyst for crustal melting and magmatic recycling sm nd isotopic signatures of 1 8 1 4 ga volcanic and plutonic rocks in southwestern colorado lend evidence to the emplacement of melts from depleted mantle and juvenile crust in the production continental crust with minor if any contamination by crust older than 1 8 ga the proterozoic magmatic record in southwestern colorado is consistent with continental growth by the addition of juvenile crust extracted from the mantle followed by periodic intracrustal growth during orogenic pulses in which mantle magmas underplate and melt the crust with consequent thickening

paleomagnetism of the middle proterozoic electra lake gabbro needle mountains southwestern colorado the electra lake gabbro is a small 1 435 ga pluton that intrudes 1 7 to 1 6 ga gneisses and schists of the needle mountains in southwestern colorado paleomagnetic samples were collected from the main phases of the gabbro diabase dikes granite and alaskite dikes that cut the gabbro and from a partially melted zone in gneiss along the southern margin of the pluton gabbro diabase and some melt zone samples have a single polarity characteristic magnetization of northeast declination d and moderate negative inclination i demagnetization behavior and rock magnetic characteristics indicate that the remanence is carried by nearly pure magnetite after correction for the minor west dip of overlying paleozoic strata we obtain a mean direction of d 32 1 i 41 9 k 94 95 3 3 n 21 sites and a paleomagnetic pole at 21 1 s 221 1 e k 89 a95 3 4 this pole is similar to poles from the middle proterozoic belt supergroup but is located at a higher southerly latitude than poles from other 1 47 1 44 ga plutons from north america most of which plot at equatorial latitudes the reason for this discrepancy is not clear but may result from a combination of factors including unrecognized tilting of the gabbro the failure of this relatively small pluton to fully average paleosecular variation and uncertainties in the overall reliability of other 1 5 1 4 ga poles of the north american apparent polar wander path

intensity of the geomagnetic field in europe for the last 3 ka influence of data quality on geomagnetic field modeling one of the main challenges of paleomagnetic research is to obtain high resolution geomagnetic field intensity reconstructions for the last millennia these reconstructions are mostly based on archeomagnetic data however the quality of the intensity data available in the databases is very variable and the high scatter observed in the records clearly suggests that some of them might not be reliable in this work we investigate how the geomagnetic field intensity reconstructions and hence our present knowledge of the geomagnetic field in the past are affected by the quality of the data selected for modeling the earth s magnetic field for this purpose we rank the european archeointensity data in four quality categories following widely accepted paleomagnetic criteria based on the methodology used during the laboratory treatment of the samples and on the number of specimens retained to calculate the mean intensities four geomagnetic field regional models have been implemented by applying the revised spherical cap harmonic analysis to these four groups of input data geomagnetic field models strongly depend on the used data set the model built using all the available data without any preselection appears to be the less accurate indicating some internal inconsistencies of the data set in addition some features of this model are clearly dominated by the less reliable archeointensity data suggesting that such features might not reflect real variations of the past geomagnetic field on the contrary the regional model built on selected high quality intensity data shows a very consistent intensity pattern at the european scale confirming that the main intensity changes observed in europe in the recent history of the geomagnetic field occurred at the continental scale

new late neolithic c 7000 5000 bc archeointensity data from syria reconstructing 9000years of archeomagnetic field intensity variations in the middle east we present new archeomagnetic intensity data from two late neolithic archeological sites tell halula and tell masaikh in syria these data from 24 groups of potsherds encompassing 15 different time levels are obtained using the triaxe experimental protocol which takes into account both the thermoremanent magnetization anisotropy and cooling rate effects on intensity determinations they allow us to recover the geomagnetic intensity variations in the middle east between 7000 bc and 5000 bc i e during the so called pre halaf proto halaf halaf and halaf ubaid transitional cultural phases the data are compared with previous archeointensity results of similar ages from northern iraq yarim tepe ii and tell sotto and bulgaria we find that previous dating of the iraqi material was in error when corrected all northern mesopotamian data show a relatively good consistency and also reasonably match with the bulgarian archeointensity dataset using a compilation of available data we construct a geomagnetic field intensity variation curve for the middle east encompassing the past 9000 years which makes it presently the longest known regional archeomagnetic intensity record we further use this compilation to constrain variations in dipole field moment over most of the holocene in particular we discuss the possibility that a significant dipole moment maximum occurred during the third millennium bc which cannot easily be identified in available time varying global geomagnetic field reconstructions

summertime enso north african asian jet teleconnection and implications for the indian monsoons 1 recent findings indicate that enso may modulate the strength of the indian monsoons by altering the meridional tropospheric temperature gradient between asia and the equatorial indian ocean here we show that during northern hemisphere summertime el nino events both colder upper tropospheric temperatures and increased vorticity anomalies are observed within the north african asian naa jet the temperature response within the naa jet is the dominant enso related change to the meridional tropospheric temperature gradient between asia and the equatorial indian ocean forced solutions of the linearized barotropic vorticity equation indicate that these anomalies within the naa jet are a response to northern hemisphere summertime el nino related convective activity over the equatorial pacific ocean additional experiments indicate that westward propagating anomalies in both the tropics and middle latitudes produce the anomaly response within the naa jet these findings suggest that the teleconnection linking enso and the monsoons is mediated by the response of the naa jet to westward propagating rossby waves citation shaman j and e tziperman 2007 summertime enso north african asian jet teleconnection and implications for the indian monsoons geophys res lett 34 l11702 doi 10 1029 2006gl029143

a new three axis vibrating sample magnetometer for continuous high temperature magnetization measurements applications to paleo and archeo intensity determinations we have developed a new three axis vibrating sample magnetometer which allows continuous high temperature magnetization measurements of individual cylindrical 0 75 cm3 samples up to 650 c and the acquisition of thermoremanent magnetization trm in any direction and field intensity up to 200 t we propose a fast less than 2 5 h automated experimental procedure adapted from boyd s nature 319 1986 208 209 modified version of the thellier and thellier ann geophys 15 1959 285 376 method which provides continuous intensity determinations over a large typically 300 c temperature interval for each sample this procedure allows one to take into account both the cooling rate dependence of trm acquisition and anisotropy of trm several examples of analyses of ancient magnetization demonstrate the quality and reliability of the data and illustrate the promising potential of this new instrument in paleo and archeomagnetism

new constraints on the most significant paleointensity change in western europe over the last two millennia a non dipolar origin over the last years new evidences of several short lived regional maxima of the geomagnetic field intensity at various times and locations have been defined these features have important implications both for geomagnetic field modeling and for earth s dynamo simulations however the nature extent and underlying causes of these variations are still poorly understood the major constraint for an adequate description of these important features is the absence of continuous detailed records and the current limited availability of precisely dated geomagnetic field recorders in this context archeological materials from superimposed strata covering long sequences of occupation provide a powerful tool to investigate the temporal variability of geomagnetic field strength at decadal and centennial time scales in this work we report the archeomagnetic study of 79 potteries from southeastern spain collected in 14 different stratigraphic units the chronological framework of the studied collection ranging from the 9th to the 12th centuries is based on historical archeological data such as written sources and well established typological and archeometric documentation on ceramics found on reference contexts in the area additionally two radiocarbon dates obtained from two different stratigraphic units confirm the proposed chronological intervals from classical thellier and thellier experiments including partial thermoremanent magnetization ptrm checks and trm anisotropy and cooling rate corrections height new high quality mean intensities were derived the new data provide an improved description of the sharp abrupt intensity decay that took place in western europe after the 800 ad intensity maximum the most significant geomagnetic field intensity feature observed in europe over the last two millennia the new results confirm that several rapid intensity changes with rates higher than 10 t century took place in western europe during the recent history of the earth the comparison between the regional curve of western europe and the sha dif 14k global field model predictions suggests that the 800 ad event observed in europe is probably controlled by non dipolar geomagnetic sources

the steens mountain oregon geomagnetic polarity transition 2 field intensity variations and discussion of reversal models we carried out an extensive paleointensity study of the 15 5 0 3 m y miocene reversed to normal polarity transition recorded in lava flows from steens mountain south central oregon one hundred eighty five samples from the collection whose paleodirectional study is reported by mankinen et al this issue were chosen for paleointensity investigations because of their low viscosity index high curie point and reversibility or near reversibility of the strong field magnetization curve versus temperature application of the thellier stepwise double heating method was very successful yielding 157 usable paleointensity estimates corresponding to 73 distinct lava flows after grouping successive lava flows that did not differ significantly in direction and intensity we obtained 51 distinguishable complete field vectors of which 10 are reversed 28 are transitional and 13 are normal the record is complex quite unlike that predicted by simple flooding or standing nondipole field models it begins with an estimated several thousand years of reversed polarity with an average intensity of 31 5 8 5 t about one third lower than the expected miocene intensity this difference is interpreted as a long term reduction of the dipole moment prior to the reversal when site directions and intensities are considered truly transitional directions and intensities appear almost at the same time at the beginning of the transition and they disappear simultaneously at the end of the reversal large deviations in declination occur during this approximately 4500 1000 year transition period that are compatible with roughly similar average magnitudes of zonal and nonzonal field components at the site the transitional intensity is generally low with an average of 10 9 4 9 t for directions more than 45 away from the dipole field and a minimum of about 5 t the root mean square of the three field components x y and z are of the same order of magnitude for the transitional field and the historical nondipole field at the site latitude however a field intensity increase to pretransitional values occurs when the field temporarily reaches normal directions which suggests that dipolar structure could have been briefly regenerated during the transition in an aborted attempt to reestablish a stationary field changes in the field vector are progressive but jerky with at least two and possibly three large swings at astonishingly high rates each of those transitional geomagnetic impulses occurs when the field intensity is low less than 10 t and is followed by an interval of directional stasis during which the magnitude of the field increases greatly for the best documented geomagnetic impulse the rapid directional change corresponds to a vectorial intensity change of 6700 2700 nt yr 1 which is about 15 50 times larger than the maximum rate of change of the nondipole field observed during the last centuries the occurrence of geomagnetic impulses seems to support reversal models assuming an increase in the level of turbulence within the liquid core during transitions the record closes with an estimated several thousand years of normal polarity with an average intensity of 46 7 20 1 t agreeing with the expected miocene value however the occurrence of rather large and apparently rapid intensity fluctuations accompanied by little change in direction suggests that the newly reestablished dipole was still somewhat unstable

ensembles of low degree archeomagnetic field models for the past three millennia abstract we introduce ensembles of time varying archeomagnetic field models consisting of a reference model a mean model and a thousand individual models we present a set of three such ensembles built from archeomagnetic volcanic and sedimentary data sets that cover the past three millennia these ensembles can be used to describe the field at any location from the core surface to the magnetosphere and assess the way uncertainties due to the limited distribution and quality of the data affect any of its component or parameter such as individual gauss coefficients they provide alternative and we argue more complete descriptions of the archeomagnetic field to those provided by previously published archeomagnetic field models being better suited to existing and emerging needs such as those of geomagnetic data assimilation we present the data sets we rely on essentially the same as those used by other recent archeomagnetic field models and describe how errors affecting the data and errors due to non modelled small spatial scales of the field are taken into account we next explain our modeling strategy and motivation for building low degree spherical harmonic degree ensembles of models we carry on a number of end to end simulations to both illustrate the usefulness of such ensembles and point at the type of errors one should expect practical illustrations of what can be done with these three ensembles of models with examples of geomagnetic inferences are also described northern high latitude flux patches for instance appear to be the most robust features of all these patches tend to fluctuate but clearly have some favored locations resulting in the same clear signature with three tongues over northern america europe and asia in the time averaged field at the core mantle boundary similar to what had been found in earlier models inferences about the field behavior in the southern hemisphere are more difficult to draw still some suggestions that the well known present south atlantic reversed patch could have arisen as early as in 1500 a d are found in some of the ensembles we otherwise confirm that most of the current archeomagnetic field model limitations are related to a number of sediment cores identified as producing frequent outliers in the modeling process we provide evidence that such cores are likely affected by timing errors and timing delays between magnetization lock in and sediment deposition that future more advanced treatment should be able to handle all source files for the three ensembles of models together with appropriate matlab applications can be downloaded from http geomag ipgp fr download archeo fm zip

mesoproterozoic trans laurentian magmatism a synthesis of continent wide age distributions new sims u pb ages zircon saturation temperatures and hf and nd isotopic compositions abstract the origin and tectonic setting of the mesoproterozoic 1 50 1 34 ga granite rhyolite provinces of the midcontinent region of the united states and the coeval a type granite plutons of the southwestern united states have been an enigma for decades in this paper we review the history of this problem examine the significance of a wealth of previously published u pb zircon and whole rock sm nd data and present new u pb zircon age and lu hf isotopic data from selected zircon samples our data show that the initiation of this magmatism spans the interval 1 50 1 40 ga across the continent but there is a general younging westward younger 1 39 1 34 ga magmatism also occurred across the continent but forms a major magmatic event only in the south central mid continent there is generally a good correlation between sm nd and lu hf isotopic compositions and inferred mantle derivation model ages except possibly in southeastern oklahoma the absence of older cores in zircons is compatible with calculated zircon saturation temperatures of ca 850 c and supports mantle driven basaltic underplating and resulting crustal partial melting as a petrogenetic model for the a type magmatism our new data compilation refines the existence of the nd line that extends from southwestern texas into southeastern michigan and the western grenville province in canada it marks an isotopic boundary between granites and rhyolites of cratonal origin to the northwest 1 8 1 6 ga model ages and those of more juvenile origin to the southeast 1 5 1 4 ga model ages our suggested tectonic model for the mesoproterozoic a type magmatism across eastern and southern laurentia involves the development of an active laurentian margin extending from eastern canada across what is now the midcontinent region of the united states and at least into the current southwestern united states magmatism along this margin was likely related to asthenosphere lithosphere interactions associated with the accretion of outboard arcs and possible exotic terranes that caused complex deformational and magmatic responses in the continental interior this activity evidently spread from northeast to southwest over a period of ca 70 million years the occurrence of the younger ca 1 39 1 34 ga event indicates that similar processes occurred some 130 million years later suggesting a long lived convergent plate margin and recurring basaltic underplating in some locations perhaps due to inboard lithospheric delamination and or mantle upwelling

geomagnetic paleointensity between 1300 and 1750 a d derived from a bread oven floor sequence in lubeck germany geomagnetic paleointensities have been determined from a single archaeological site in lubeck germany where a sequence of 25 bread oven floors has been preserved in a bakery from medieval times until today age dating confines the time interval from about 1300 a d to about 1750 a d paleomagnetic directions have been published from each oven floor and are updated here the specimens have very stable directions and no or only weak secondary components the oven floor material was characterized rock magnetically using thellier viscosity indices median destructive field values curie point determinations and hysteresis measurements magnetic carriers are mixtures of sd psd and minor md magnetite and or maghemite together with small amounts of hematite paleointensity was measured from selected specimens with the double heating thellier method including ptrm checks and determination of trm anisotropy tensors corrections for anisotropy as well as for cooling rate turned out to be unnecessary ninety two percent of the thellier experiments passed the assigned acceptance criteria and provided four to six reliable paleointensity estimates per oven floor mean paleointensity values derived from 22 oven floors show maxima in the 15th and early 17th centuries a d followed by a decrease of paleointensity of about 20 until 1750 a d together with the directions the record represents about 450 years of full vector secular variation the results compare well with historical models of the earth s magnetic field as well as with a selected high quality paleointensity data set for western and central europe

geomagnetic field hemispheric asymmetry and archeomagnetic jerks abstract we investigate the origin of the so called archeomagnetic jerks detected in the french archeomagnetic record over the past three millennia although only very large scale global archeomagnetic field models are currently available we show that the occurrence of archeomagnetic jerks is intimately linked to what we define as most eccentric events i e periods of time when a simple description of the geomagnetic field in terms of an eccentric dipole reveals the center of this eccentric dipole to strongly move away from the earth s center from the behavior of the much better known historical field we interpret the evolution of the center of the eccentric dipole as reflecting the production and gathering of flux patches at the core mantle boundary within preferential hemispheres archeomagnetic jerks would thus correspond to episodes of maximum geomagnetic field hemispheric asymmetry such most eccentric events could also provide an explanation for some of the properties previously reported in the long term paleomagnetic field

intensity of the earth s magnetic field in greece during the last five millennia new data from greek pottery abstract new archaeointensity results have been obtained from the study of four ceramic collections coming from four different archaeological sites in greece the ages of the ceramic fragments based on archaeological constrains and radiocarbon analysis range from 2200 bc to 565 ad low field magnetic susceptibility versus temperature reveals a good thermal stability for most of the samples however for some samples the thermomagnetic curves are not reversible indicating mineralogical changes during heating isothermal remanent magnetisation irm acquisition curves and thermal demagnetisation of three orthogonal irm components have also been performed the rock magnetic results identify magnetite and or ti magnetite as the main magnetic carriers in the studied samples classical thellier experiments with regular partial thermoremanent magnetisation ptrm checks have been conducted on 125 specimens belonging to 34 independent ceramic fragments only 61 archaeointensity determinations at specimen level that correspond to linear nrm trm plots were used for the calculation of the site mean archaeointensities the effect of the anisotropy of the thermoremanent magnetisation trm and cooling rate upon trm intensity acquisition have been investigated in all specimens the maximum difference between the trm anisotropy corrected and uncorrected intensities is around 30 at specimen level confirming that the trm effect can be very important in ceramic samples cooling rate correction factors determined per specimen are up to 10 with only one exception that reaches 35 despite the moderate success rate of archaeointensity determination around 50 reliable mean site intensities have been obtained with in situ intensities ranging from 53 6 4 1 to 69 3 3 9 t corresponding to virtual axial dipole moments from 9 2 0 7 to 11 9 0 7 10 22 am 2 the new data are reasonably consistent with other available data for the studied region as well as with the sv reference curves for greece and the south balkan peninsula and the regional and global geomagnetic field models combined with previously published data from the area they confirm that important changes of the earth s magnetic field intensity occurred in greece during the last five millennia for some periods the available archaeointensity data for the balkan area show a large dispersion even for data corresponding to high quality intensity standards whereas for other periods their limited number prevents an accurate description of geomagnetic field intensity changes this evidences the need of new reliable and well dated archaeointensity data in order to obtain a robust description of geomagnetic field intensity changes during the last five millennia in this area

syncontractional crustal anatexis and deformation during emplacement of 1435 ma plutons western needle mountains colorado mesoproterozoic deformation and biomodal magmatism in southwest colorado offer important insight into the nature and tectonic regime of 1 4 ga magmatism in the western united states we document syncontractional emplacement of coeval gabbroic and granitic plutons in the middle crust at 1435 ma in the western needle mountains this is incompatible with extension dominated anorogenic models proposed for the generation of 1 4 ga plutonic rocks in the southwest but lends further support for synkinematic intracontinental magmatism in response to regional tectonic strains created by transpressive or compressive plate margin interactions between 1500 1300 ma intrustion of the 1435 ma electra lake gabbro and eolus granite into paleoproterozoic rocks caused local crustal anatexis and extensive thermal metamorphism in the needle mountains deformation of paleoproterozoic country rocks at 1435 ma is widespread but is concentrated in pluton aureoles where thermally softened crust accommodated the strain we int

fabric reactivation an example from the hualapai mountains nw arizona usa abstract foliation reactivation involves renewed movement on preexisting fabrics and can lead to difficulty in determining temporal and spatial relationships of fabrics to larger structures as well as correlation of fabrics to tectonic events porphyroblasts that contain internal fabrics allow for interpretation of the structural history of an area including the potential for foliation reactivation in boriana canyon hualapai mountains nw arizona three vertical foliations s 2 s 4 are preserved in the contact aureole of the 1 40 ga boriana granite foliation s 2 strikes northeast and is parallel with regional foliation that formed post or syn 1 68 ga foliation s 3 occurs throughout the canyon but is most prevalent in the contact aureole where close to the pluton it forms the main cleavage andalusite and garnet porphyroblasts overgrew s 3 crenulations foliation s 4 is parallel to the s 2 regional fabric and in some outcrops deformation associated with s 4 has decrenulated the s 3 fabric although s 3 is preserved in garnet and andalusite porphyroblasts in these outcrops s 4 is also axial planar to f 2 folds recognition of fabric reactivation of this aureole allows for discrimination of foliation forming episodes that are separated by 250 m y and a better understanding of the proterozoic geologic history for this part of nw arizona

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

delayed enso impact on spring precipitation over north atlantic european region the delayed impact of winter sea surface temperature sst anomalies in tropical pacific on spring precipitation over the north atlantic european nae region is examined using both measured and modeled data for the period 1901 2002 in an amip type atmospheric general circulation model agcm ensemble the observed delayed spring precipitation response in europe to winter enso related sst anomalies is well reproduced a series of targeted agcm coupled gcm experiments are performed to further investigate the mechanisms for this delayed influence it is found that late winter enso sst anomalies lead to the well documented rossby wave train arching from the pacific into the atlantic region a positive negative enso event leads to a quasi barotropic trough ridge in the north atlantic region the resulting wind and cloud changes cause anomalies in the surface heat fluxes that result in negative positive sst anomalies in the central north atlantic and anomalies of the opposite sign further to the south the sst anomalies persist into spring and the atmospheric response to these anomalies is an extension of the enso induced trough ridge into the european region leading to enhanced reduced moisture flux and low level convergence divergence and thus positive negative precipitation anomalies although the signal is overall relatively weak correlation coefficients of european spring rainfall with winter enso ssts of about 0 3 a proper representation of the outlined mechanism in seasonal forecasting systems may lead to improved seasonal predictions

periodicity in stromatolitic lamination a potential record of enso nao and sunspot in the miocene lacustrine record of the ebro basin spain abstract the spectral decomposition of time series obtained from ancient rock records can be used to study the similarity between the dynamics of present day and past climate systems a high resolution periodicity analysis of luminance and lamina thickness of lacustrine stromatolites in the ebro basin northeast of iberian peninsula reveals a significant signal of interannual and decadal climatic variability in the miocene this is one out of very few works that presents the use of spectral analysis to estimate the potential of stromatolite lamination as multiple scale recorders of climate parameters the effects of precipitation and evaporation variations on stromatolite lamination have been detected at three orders of cyclicity based on textural and high resolution stable isotope analyses c and o obtained in prior studies these analyses also revealed that the light and dark simple lamina couplets are identified with annual cycles third order isotopic cycles in the present study the spectral analysis results obtained through different paths in five stromatolite specimens reveal significant periods in the power spectrum at around 2 5 3 7 5 7 10 and 22 years these cycles can be correlated with the typical oscillation bands of different climate related agents the 2 5 year period corresponds to the quasi biennial oscillation qbo or to the biennial component of the el nino southern oscillation enso or to the north atlantic oscillation nao the 3 to 5 and 5 to 7 year bands can be linked to enso or nao variability second order isotopic cycles the 8 to 11 year bands fit the 11 year schwabe first order isotopic cycles and 22 to 23 year fit the 22 year hale sunspot cycles thus the stromatolite growth was controlled by enso nao and solar activity cycles the close relationship between these climate related agents makes it difficult to specify the dominant agent controlling the stromatolite growth nevertheless the significant periods obtained from this study within interannual 2 5 3 7 5 7 years decadal 10 22 years and even multidecadal bands 37 42 years support the existence and concurrence of enso and nao precursors during the early and middle miocene

synkinematic intrusion of the 1 4 ga boriana canyon pluton northwestern arizona implications for ca 1 4 ga regional strain in the western united states abstract the transcontinental belt of ca 1 4 ga granite plutons that extends from southern california to labrador has conventionally been interpreted as either anorogenic or emplaced in an extensional tectonic setting recent studies in the western united states however demonstrate that several ca 1 4 ga plutons were emplaced in a broadly northwest southeast shortening strain field our study of the documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewcommand sfdefault wncyss renewcommand encodingdefault ot2 normalfont selectfont declaretextfontcommand textcyr cyr pagestyle empty declaremathsizes 10 9 7 6 begin document landscape 1404 1 5 end document ma boriana canyon pluton northwestern arizona est

extended and revised archaeomagnetic database and secular variation curves from bulgaria for the last eight millennia the efforts of geophysicists to describe geomagnetic field behaviour in the past lead to creation of different geomagnetic field models on the other hand the established regional palaeosecular variations of geomagnetic elements are increasingly used for dating purposes in archaeology both of these goals can be achieved if sufficient amounts of long archaeomagnetic data sets exist for different geographical regions the accumulation of archaeomagnetic determinations began at the middle of the last century parallel with the progressive development of experimental methodology and acceptance criteria the presence of great number of old determinations requires their critical assessment the important question about the reliability of the associated dating intervals should be also re assessed all this requires the continuous refinement and extension of the accumulated databases this paper presents the last synthesis of bulgarian archaeomagnetic database and the local palaeosecular variation curves obtained using a statistical treatment based on bayesian approach rencurve software the rock magnetic characteristics of the newly included non published results are summarized

improving geomagnetic field reconstructions for 0 3 ka global geomagnetic field reconstructions on millennial time scales can be based on comprehensive paleomagnetic data compilations but especially for older data these still suffer from limitations in data quality and age controls as well as poor temporal and spatial coverage here we present updated global models for the time interval 0 3 ka where additions to the data basis mainly impact the south east asian alaskan and siberian regions we summarize recent progress in millennial scale modelling documenting the cumulative results from incremental modifications to the standard algorithms used to produce regularized time varying spherical harmonic models spanning 1000 bc to 1990 ad from 1590 to 1990 ad gauss coefficients from the historical gufm1 model supplement the paleomagnetic information in addition to absolute paleointensities calibrated relative paleointensity data from sediments are now routinely included iterative data rejection and recalibration of relative intensity records from sediments ensure stable results bootstrap experiments to generate uncertainty estimates for the model take account of uncertainties in both age and magnetic elements and additionally assess the impact of sampling in both time and space based on averaged results from bootstrap experiments taking account of data and age uncertainties we distinguish more conservative model estimates cals3k nb representing robust field structure at the core mantle boundary from relatively high resolution models cals3k n for model versions n 3 and 4 we assess the impact of newly available data and modifications to the modelling method by comparing the previous cals3k 3 the new cals3k 4 and the conservative new model cals3k 4b we conclude that with presently available data it is not feasible to produce a model that is equally suitable for relatively high resolution field predictions at earth s surface and robust reconstruction of field evolution avoiding spurious structure at the core mantle boundary cmb we presently consider cals3k 4 the best high resolution model and recommend the more conservative lower resolution version for studies of field evolution at the cmb

archaeomagnetic study of five mounds from upper mesopotamia between 2500 and 700 bce further evidence for an extremely strong geomagnetic field ca 3000 years ago the distribution of archaeomagnetic data in eastern europe and the near and middle east shows a remarkable gap in turkey this study presents the first archaeomagnetic results from five different mounds in southeast turkey the northern part of mesopotamia the rock magnetic experiments indicate that in the majority of the samples the dominant magnetic carrier is magnetite which is stable to heating to temperatures of 700 1c in general the demagnetization diagrams are single component and all five sets display well defined characteristic magnetizations and clustered directions for the period between 2500 and 700 bce the declinations are between 3501 and 201 while inclinations are in the range of 49 641 the directional results are compared with the global geomagnetic field models cals7k 2 arch3k cst 1 and cals3k 4 and the data from the archaeomagnetic database geomagia50v2 the results are coherent with both the data and the models except for two nearcontemporaneous sets dating 2000 bce which are offset to the east by more than 201 with respect to cals7k 2 archaeointensity measurements were made using the microwave and conventional thermal thellier methods applied to five sets of samples four furnaces and a mud brick wall these yielded comparable and intriguing results while those from the furnaces are slightly higher than the cals7k 2 model and in agreement with the geomagia50v2 and the middle east data the results from the mud brick wall suggest a high intensity of 100 8 mt 17 7 10 22 am 2 a t 1000 bce this result is

on the possible occurrence of archaeomagnetic jerks in the geomagnetic field over the past three millennia abstract archaeomagnetism can provide a high resolution full vector description of the earth s magnetic field for the past several thousand years we analyse the bulk of archaeomagnetic data both direction and intensity obtained recently in western europe and the eastern mediterranean covering the past three millennia we demonstrate a remarkable coincidence between sharp cusps in geomagnetic field direction and intensity maxima two clear ones at ad 200 and 1400 two presently less well constrained at 800 bc and ad 800 these sharp changes may constitute a new feature of geomagnetic secular variation archaeomagnetic jerks with time characteristics intermediate between geomagnetic jerks and magnetic excursions

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

geomagnetic field intensity during the last 60 000 years based on 10be and 36cl from the summit ice cores and 14c abstract based on 10 be 36 cl and 14 c records we reconstruct past changes in the geomagnetic field intensity under the assumption that radionuclide records are mainly influenced by changes in their production rates subsequent comparison of these records with independent geomagnetic field reconstructions allows us to assess the reliability of our approach and to identify periods where our method or the geomagnetic field reconstructions might be problematic the geomagnetic field derived from the 10 be flux to summit in central greenland agrees well with independent geomagnetic field intensity reconstructions however compared to independent palaeomagnetic data the radionuclide record suggests increased geomagnetic field intensities especially for the period from 20 000 to 30 000 years bp 36 cl from the grip ice core agrees well with the 10 be record for the last ice age and hence also the reconstructed geomagnetic field based on the tree ring radiocarbon record it is possible to reconstruct geomagnetic field intensity changes during the holocene a comparison of radiocarbon based and independent geomagnetic field reconstructions indicates that changes in the carbon cycle significantly influenced the atmospheric radiocarbon concentration before 10 000 years bp

paleoclimate of the southern adriatic sea region during the medieval climate anomaly reflected by organic walled dinoflagellate cysts to obtain insight into the character and forcing of southern italian climate change during the medieval climate anomaly c ad 900 1200 marine sediments deposited between ad 990 and 1200 from t

shrimp rg u pb zircon geochronology of mesoproterozoic metamorphism and plutonism in the southwesternmost united states abstract mesoproterozoic intrusive and granulite grade metamorphic rocks in southern california have been inferred to be exotic to north america on the basis of perceived chronologic incompatibility with autochthonous cratonal rocks ion microprobe geochronology indicates that zircons in granulite grade gneisses dated at 1 4 ga using conventional methods are composed of 1 68 1 80 ga cores and 1 19 ga rims these early proterozoic gneisses were metamorphosed at extremely high temperatures and moderate pressures during emplacement of the 1 19 ga san gabriel anorthosite complex the lack of a 1 4 ga metamorphic event suggests that proterozoic rocks in this region rather than being exotic to north america may in fact be a midcrustal window into mesoproterozoic crustal evolutionary processes in southwestern north america

geomagnetic intensity variations for the past 8 kyr new archaeointensity results from eastern china abstract in this study we have carried out paleointensity experiments on 918 specimens spanning the last 7 kyr including pottery fragments baked clay and slag collected from shandong liaoning zhejiang and hebei provinces in china approximately half of the specimens yielded results that passed strict data selection criteria and give high fidelity paleointensities the virtual axial dipole moments vadms of our sites range from 2 10 22 to 13 10 22 am 2 at 2250 bce our results suggest a paleointensity low of 2 10 22 am 2 which increases to a high of 13 10 22 am 2 by 1300 bce this rapid less than 1000 yrs six fold change in the paleointensity may have important implications for the dynamics of core flow at this time our data from the last 3 kyr are generally in good agreement with the arch3k 1 model but deviate significantly at certain time periods from the cals3k 4 and cals10k 1b model which is likely due to differences in the data used to constrain these models at ages older than 3 ka where only the cals10k 1b model is available for comparison our data deviate significantly from the model combining our new results with the published data from china and japan we provide greatly improved constraints for the regional model of eastern asia when comparing the variations of geomagnetic field in three global representative areas of eastern asia the middle east and southern europe a common general trend of sinusoidal variations since 8 ka is shown likely dominated by the dipole component however significant disparities are revealed as well which we attribute to non dipolar components caused by movement of magnetic flux patches at the core mantle boundary

the superposition of eastward and westward rossby waves in response to localized forcing abstractrossby waves are a principal form of atmospheric communication between disparate parts of the climate system these planetary waves are typically excited by diabatic or orographic forcing and can be subject to considerable downstream modification because of differences in wave properties including vertical structure phase speed and group velocity rossby waves exhibit a wide range of behaviors this study demonstrates the combined effects of eastward propagating stationary barotropic rossby waves and westward propagating very low zonal wavenumber stationary barotropic rossby waves on the atmospheric response to wintertime el nino convective forcing over the tropical pacific experiments are conducted using the community atmosphere model version 4 0 in which both diabatic forcing over the pacific and localized relaxation outside the forcing region are applied the localized relaxation is used to dampen rossby wave propagation to either the west or east of the forcing region and isolate the al

core flow constraints on extreme archeomagnetic intensity changes abstract recent studies ben yosef et al 2009 shaar et al 2011 propose extreme archeomagnetic intensity changes termed spikes in the range 4 5 t year c a 1000 bc in the near east around 40 to 50 times larger than values typical of the present day in order to investigate whether such extreme changes are consistent with a model of the source region of the magnetic field namely the fluid flow at the surface of earth s core we construct upper bounds for instantaneous magnetic intensity change at an arbitrary site on the earth s surface these bounds are constrained by the amount of kinetic energy available to sustain the change taken here to be a prescribed value for the root mean squared surface velocity of 13 km yr as inferred from the current state of the core further we focus attention on two end members of optimised core surface flow structure unrestricted and purely toroidal as the derivation of the bounds demands complete knowledge of the geomagnetic field at the core surface we model the unknown field by means of a monte carlo approach extending to high degree the chaos 4 epoch 2010 ad and cals10k1 b epoch 1000 bc geomagnetic field models using 2000 realisations for each family of stochastic field models we find that optimised core flows are always large scale and that they tend to generate a non dipole quadrupole dominated secular variation at the earth s surface the dependence of the upper bounds as a function of site location reflects the large scale structure of the intensity itself stronger field permits more rapid change for the site in the near east purely toroidal flows have upper bounds of approximately 0 62 0 02 t year whereas unrestricted flows increase this bound to 1 20 0 02 t year we favour the former as more geophysically sound on the account of a large body of previous results from core surface flow inversions and consistency with the existence of a stratified layer at the top of the core even if we allow for a generous threefold increase in the prescribed rms velocity and a concomitant threefold increase in the bound we conclude that the reported occurrences of extreme intensity changes as suggested in the near east are not compatible with the commonly accepted structure of core surface flow however it may be that an explanation for spikes lies beyond our current perception of core dynamics and future work would be further motivated by seeking corroborative evidence of rapid intensity change from sites elsewhere on earth s surface we therefore also discuss the form that the secular variation would take in the case of simultanenous archeomagnetic spikes

the seasonal effects of enso on atmospheric conditions associated with european precipitation model simulations of seasonal teleconnections abstractthe seasonal upper tropospheric teleconnection between enso and the north atlantic european sector is explored through a series of model experiments a barotropic vorticity equation model is linearized about climatological conditions for each season of the year and divergence forcing is applied over the equatorial pacific to mimic el nino related convective activity during boreal fall winter and spring this forcing similarly excites a northeastward propagating stationary barotropic rossby wave train that extends across the north atlantic to the european coast strong anomalies develop over the british isles in the vicinity of the north atlantic jet exit solutions during boreal summer produce no clear wave train however evidence exists for a north atlantic response because of both eastward and westward propagating signals these direct responses over the atlantic and europe are qualitatively similar to observed enso associated anomalies during boreal spring and fall but differ structurall

mechanisms of eastern mediterranean rainfall variability abstract this paper presents a simple theory for the association between observed eastern mediterranean em rainfall anomalies and north atlantic na climate variability large scale na atmospheric mass rearrangements primarily a modulation of the icelandic low and the subtropical high pressure systems tend to extend beyond the na a particularly strong such teleconnection exists between the northern na and southern europe and the mediterranean basin pressure anomalies over greenland iceland are thus associated with reversed polarity anomalies centered over the northern adriatic affecting the entire mediterranean basin elevated greenland pressure is accompanied by an anomalous cyclone over the mediterranean and a mediterranean high pressure system is present when pressure over greenland is reduced in the em these anomalies result in anomalous southerlies during greenland highs and northerlies during greenland lows eastern mediterranean southerlies warm the em while northerlies cool locally b

thermodynamics of eastern mediterranean rainfall variability abstract this note focuses on thermodynamic changes caused by eastern mediterranean em subsidence anomalies subsidence anomalies are shown to modulate em wide stability with respect to moist ascent additionally convective available potential energy cape generation rates as well as mean cape change coherently during extreme em rainfall anomalies it is suggested that the resulting modulation of convective rain generation is the process directly responsible for the observed rainfall anomalies

geomagnetic field variations in western europe from 1500 bc to 200 ad part ii new intensity secular variation curve abstract in order to extend the secular variation curve svc of archaeointensity in western europe to the first millennium bc we studied 24 kilns and hearths in place two displaced hearths and six sets of pottery sherds from french archaeological sites archaeological artefacts radiocarbon and dendrochronology dated the acquisition of the thermoremanent magnetization trm carried by the studied objects rock magnetism experiments suggest that the main carrier of the magnetization is a ti poor titanomagnetite archaeointensity was determined by the thellier thellier classical protocol with ptrm checks a strict criteria set was applied to select only the most reliable results with linear nrm trm diagrams 55 of total specimens this study demonstrates that pottery sherds with two trms give reliable archaeointensities in the low temperature interval if the nrm trm diagram is adequately adjusted eighteen new mean archaeointensities 14 corrected from the anisotropy of trm and 16 from cooling rate were computed the comparison with previously published western europe paleointensities show a strong dispersion between data primarily due to their variable quality western europe data were weighted following the archaeointensity protocol the number of specimens per site and the type of studied materials in order to better highlight the secular variation of archaeointensity during the first millennium bc the svc built with sliding windows of 160 years shifted every 50 years presents at paris a maximum of 90 t around 800 bc and a minimum of 60 t around 250 bc these archaeointensity maximum and minimum correspond to cusps of the geomagnetic field direction in western europe this new curve is consistent with mesopotamian and eastern europe data the archaeointensity secular variation in western europe predicted by global geomagnetic models cals3k 4 arch3k 1 and arch3k cst 1 is smoother than our svc we used our directional dataset herve et al 2013 to build a new western europe vgps and vdms mean curves comparison with the predictions given by the global models points out a possible persistent non dipole fields effect over europe between 1000 bc and 600 500 bc finally we note that the strong variations of intensity of the geomagnetic field with a mean decrease rate per century close to 6 t will be useful for archaeomagnetic dating purposes

a geomagnetic field model for the holocene based on archaeomagnetic and lava flow data abstract we propose a new geomagnetic field model for the holocene period based on archaeomagnetic and lava flow data avoiding the use of lake sediment data the source of data comes from the geomagia50v2 database which has been updated with the new archaeomagnetic and volcanic studies published during the last 3 yr the model called sha dif 14k allows us to analyse the behaviour of the geomagnetic field for the last 14 000 yr from 12 000 bc to 1900 ad for the model construction we use the spherical harmonic analysis in space and the penalized cubic b splines in time both spatial and temporal regularization norms are used to constrain the inversion problem and applied at the core mantle boundary cmb to assure the convergence of the model for the last 3 ka the model predictions agree with those given by the global model arch3k 1 and the european model scha dif 3k for older epochs the new model presents a clear improvement in field resolution with respect to other current models of the geomagnetic field for the holocene for the last 9 ka the time evolution of the dipolar moment obtained from the dipole field shows a clear minimum between 5500 bc and 3000 bc and the well known continuous decreasing trend of the geomagnetic field strength for the last millennium and a half a general view of the time average evolution of the geomagnetic field flux lobes at the cmb for the northern hemisphere suggests a marked lobe of positive magnetic flux when the dipole moment was maximum this lobe vanishes when the dipolar field is decreasing the north polar wander paths of both north magnetic dip and geomagnetic poles were obtained showing an average rate of motion of 5 1 km yr and 3 7 km yr respectively the model shows that the geomagnetic field can be averaged as axial dipolar in 2000 yr within an error of 5 the typical uncertainty of the palaeomagnetic studies finally and following the recent definition of archaeomagnetic jerks we found 8 critical events in the time evolution of the geomagnetic field for the last 8 ka characterized by a maximum in the hemispheric asymmetry of the proposed model the model is available in the earth ref digital archive at http earthref org erda 1897

the effect of enso on tibetan plateau snow depth a stationary wave teleconnection mechanism and implications for the south asian monsoons abstract an atmospheric stationary wave teleconnection mechanism is proposed to explain how enso may affect the tibetan plateau snow depth and thereby the south asian monsoons using statistical analysis the short available record of satellite estimates of snow depth and ray tracing it is shown that wintertime enso conditions in the central pacific may produce stationary barotropic rossby waves in the troposphere with a northeastward group velocity these waves reflect off the north american jet turning equatorward and enter the north african asian jet over the eastern atlantic ocean once there the waves move with the jet across north africa south asia the himalayas and china anomalous increases in upper tropospheric potential vorticity and increased wintertime snowfall over the tibetan plateau are speculated to be associated with these rossby waves the increased snowfall produces a larger tibetan plateau snowpack which persists through the spring and summer and weakens the intensity of the

an atmospheric teleconnection linking enso and southwestern european precipitation abstract numerous studies have demonstrated statistical associations between the el nino southern oscillation enso and precipitation in the mediterranean basin the dynamical bases for these teleconnections have yet to be fully identified here observational analyses and model simulations are used to show how enso variability affects rainfall over southwestern europe iberia southern france and italy a precipitation index for the region named southwestern european precipitation swep is used the observational analyses show that enso modulates swep during the september december wet season these precipitation anomalies are associated with changes in large scale atmospheric fields to the west of iberia that alter low level westerly winds and onshore moisture advection from the atlantic the vorticity anomalies associated with swep variability are linked to enso through a stationary barotropic rossby wave train that emanates from the eastern equatorial pacific and propagates eastward to the atlant

el nino modoki and its possible teleconnection 1 using observed data sets mainly for the period 1979 2005 we find that anomalous warming events different from conventional el nino events occur in the central equatorial pacific this unique warming in the central equatorial pacific associated with a horseshoe pattern is flanked by a colder sea surface temperature anomaly ssta on both sides along the equator empirical orthogonal function eof analysis of monthly tropical pacific ssta shows that these events are represented by the second mode that explains 12 of the variance since a majority of such events are not part of el nino evolution the phenomenon is named as el nino modoki pseudo el nino modoki is a classical japanese word which means a similar but different thing the el nino modoki involves ocean atmosphere coupled processes which include a unique tripolar sea level pressure pattern during the evolution analogous to the southern oscillation in the case of el nino hence the total entity is named as el nino southern oscillation enso modoki the enso modoki events significantly influence the temperature and precipitation over many parts of the globe depending on the season the impacts over regions such as the far east including japan new zealand western coast of united states etc are opposite to those of the conventional enso the difference maps between the two periods of 1979 2004 and 1958 1978 for various oceanic atmospheric variables suggest that the recent weakening of equatorial easterlies related to weakened zonal sea surface temperature gradient led to more flattening of the thermocline this appears to be a cause of more frequent and persistent occurrence of the enso modoki event during recent decades

the dynamics of the enso atlantic hurricane teleconnection enso related changes to the north african asian jet affect atlantic basin tropical cyclogenesis abstract the nature of the teleconnection linking enso variability with atlantic basin tropical storm formation is investigated solutions of the linearized barotropic vorticity equation forced with august october el nino event divergence produce upper tropospheric vorticity anomalies over the sahel and at the mouth of the north african asian naa jet over the tropical atlantic these responses are similar in magnitude and orientation to observed enso vorticity variability for this region further investigation reveals that the vorticity anomalies over the subtropical atlantic develop primarily in response to very low wavenumber westward propagating stationary rossby waves excited by el nino related convective activity over the equatorial pacific ocean however the dynamics of this teleconnection change as the atlantic basin hurricane season progresses in august and september the response is dominated by the westward propagating stationary rossby waves that alter vorticity within the naa jet and to it

variations in the geomagnetic dipole moment during the holocene and the past 50 kyr all absolute paleointensity data published in peer reviewed journals were recently compiled in the geomacia50 database based on the information in geomagia50 we reconstruct variations in the geomagnetic dipole moment over the past 50 kyr with a focus on the holocene period a running window approach is used to determine the axial dipole moment that provides the optimal least squares fit to the paleointensity data whereas associated error estimates are constrained using a bootstrap procedure we subsequently compare the reconstruction from this study with previous reconstructions of the geomagnetic dipole moment including those based on cosmogenic radionuclides be 10 and c 14 this comparison generally lends support to the axial dipole moments obtained in this study our reconstruction shows that the evolution of the dipole moment was highly dynamic and the recently observed rates of change 5 per century do not appear unique we observe no apparent link between the occurrence of archeomagnetic jerks and changes in the geomagnetic dipole moment suggesting that archeomagnetic jerks most likely represent drastic changes in the orientation of the geomagnetic dipole axis or periods characterized by large secular variation of the non dipole field this study also shows that the holocene geomagnetic dipole moment was high compared to that of the preceding similar to 40 kyr and that similar to 4 10 22 am 2 appears to represent a critical threshold below which geomagnetic excursions and reversals occur c 2008 elsevier b v all rights reserved less

on the development of strong ridge episodes over the eastern north atlantic 1 the occurrence of strong and persistent mid latitude anticyclonic ridges over the eastern north atlantic is a major contributor to the occurrence of severe winter droughts over western iberia we analyze the development of strong and persistent ridge episodes within 40 50 n 40 w 5 e which are defined as 300 hpa geopotential height anomalies above 50 gpm that persist for at least 10 consecutive days results suggest that the generation and maintenance of these episodes with positive stratospheric geopotential anomalies over the north american continent and the adjacent north pacific are associated with an intensified polar jet such positive anomalies tend to detach from the main stratospheric anomaly and propagate eastwards and downwards as rossby tropospheric waves furthermore the eastern north atlantic ridge is generated and repeatedly reinforced until the stratospheric anomaly dissipates results also show evidence for waves breaking anticyclonically during the episodes which is dynamically coherent with their persistency and quasi stationarity

40ar 39ar evidence for middle proterozoic 1300 1500 ma slow cooling of the southern black hills south dakota midcontinent north america implications for early proterozoic p t evolution and posttectonic magmatism 40ar 39ar total gas and plateau dates from moscovite and biotite in the southern black hills south dakota provide evidence for a period of middle proterozoic slow cooling early proterozoic 1600 1650 ma mica dates were obtained from metasedimentary rocks located in a synformal structure between the harney peak and bear mountain domes and also south of bear mountain metamorphic rocks from the dome areas and undeformed samples of the 1710 ma harney peak granite hpg yield middle proterozoic mica dates 1270 1500 ma two samples collected between the synform and bear mountain dome yield intermediate total gas mica dates of 1550 ma we suggest two end member interpretations to explain the map pattern of cooling ages 1 subhorizontal slow cooling of an area which exhibits variation in mica ar retention intervals or 2 mild folding of a middle proterozoic 1500 ma 300 c isotherm according to the second interpretation the preservation of older dates between the domes may reflect reactivation of a preexisting synformal structure and downwarping of relatively cold rocks during a period of approximately east west contraction and slow uplift during the middle proterozoic the mica data together with hornblende data from the black hills published elsewhere indicate that the ambient country rock temperature at the 3 4 kbar depth of emplacement of the hpg was between 350 c and 500 c suggesting that the average upper crustal geothermal gradient was 25 40 c km prior to intrusion the thermochronologic data suggest hpg emplacement was followed by a 200 m y period of stability and tectonic quiescence with little uplift we propose that crust thickened during the early proterozoic was uplifted and erosionally thinned prior to 1710 ma and that the hpg magma was emplaced into isostatically stable crust of relatively normal thickness we speculate that uplift and crustal thinning prior to hpg intrusion was the result of differential thinning of the subcrustal lithosphere beneath the black hills if so this process would have also caused an increase in mantle heat flux across the moho and triggered vapor absent melting of biotite to produce the hpg magma this scenario for posttectonic granite generation is supported in part by the fact that in the whole of the black hills the hpg is spatially associated with the deepest exposed early proterozoic country rock

new archaeomagnetic data recovered from the study of roman and visigothic remains from central spain 3rd 7th centuries summary new archaeomagnetic results from four heated combustion structures recovered from two archaeological sites in central spain are reported they have been dated by archaeological evidence and in two cases by radiocarbon dating rock magnetic experiments indicate low coercivity magnetic phases such as magnetite and thermally stable maghaemite as the main carriers of the remanent magnetization haematite has been observed in poorly heated baked clays archaeomagnetic directions have been obtained from either alternating field or thermal demagnetization experiments performed on 57 specimens coming from 46 independently oriented samples the four well defined archaeomagnetic directions obtained are in good agreement with previous archaeomagnetic data and with recent regional and global field models they define the beginning of easterly declination drift that was initiated around 350 400 ad and culminated around 800 850 ad and delineate the maximum in inclination that took place around 600 650 ad in addition classical thellier thellier experiments including thermal remanent magnetization anisotropy and cooling rate corrections were conducted on 23 specimens only 13 specimens corresponding to well defined single component behaviour gave reliable results new mean archaeointensities have been obtained for two of the four studied structures vbk1 64 2 5 0 t and vbt1 62 4 2 6 t the new data suggest that two relative intensity maxima occurred in western europe around 320 and 630 ad being of lower magnitude that observed in eastern europe

new archeointensity data from spain and the geomagnetic dipole moment in western europe over the past 2000 years archeomagnetic studies on 14 kilns a group of jar fragments and a collection of baked bricks dated between 1000 and 1959 ad plus one roman pottery kiln have been conducted in order to obtain high quality archeointensity data to enhance the western european database the thellier method with corrections for anisotropy of thermoremanent magnetization trm and for cooling rate dependence upon trm acquisition was used the effect of trm anisotropy is only important for the bricks where the corrected and uncorrected mean intensities differ by more than 5 cooling rate correction factors determined per sample are up to 15 and per site up to 7 7 our 17 new data together with 62 previously published results were used to obtain by bayesian modeling the geomagnetic field intensity over the past two millennia for western europe our results indicate that geomagnetic intensity remained more or less constant between the 1st and 4th centuries and between the 14th and 16th centuries mean values at paris around 65 and 57 t respectively whereas an important decrease occurs between 1600 and 1800 ad the detailed evolution of geomagnetic field intensity during the high middle ages is not yet well established despite their differences geomagnetic global models predict our results reasonably well this work indicates the need to obtain a number of archeointensity data for each time interval in order to reliably record variations of the geomagnetic field and to test whether any relationship exists between field intensity and climate

globally strong geomagnetic field intensity circa 3000 years ago abstract high fidelity geomagnetic field intensity determination was carried out using 191 baked fragments collected from 20 kilns or hearths with ages ranging between 1200 bc and ad 1725 in south korea geomagnetic field intensity variation displayed three narrow minima at 800 700 bc ad 700 and ad 1600 and two maxima at 1200 1100 bc and ad 1000 1100 in most time intervals virtual axial dipole moment vadm variation is confined within 20 of the present vadm however geomagnetic field intensity circa 3000 yr ago is nearly 40 larger than the present value such high vadms circa 3000 yr ago are in phase with those in other longitudinal bands in northern hemisphere centered at 5e france 30e the middle east and 200e hawaii although strong geomagnetic field intensity circa 3000 yr ago is globally synchronous the highest vadm occurs at slightly different time intervals in different locations hence it is possible that the globally strong geomagnetic field intensity circa 3000 yr ago reflects the migration of persistent hemispheric flux in northern hemisphere or an episode of geomagnetic field hemispheric asymmetry

evidence for rapid geomagnetic field intensity variations in western europe over the past 800 years from new french archeointensity data abstract the number of reliable archeointensity determinations obtained from western europe for the past millennium remains limited moreover the large scatter between different datasets available is puzzling the present study analyzed 31 new groups of baked clay ceramic or brick fragments sampled in france 29 groups and in belgium 2 groups these groups contain several fragments collected from different artefacts and are precisely dated principally from historical constraints between the xiiith and the xixth centuries additionally we re evaluated 14 intensity values that we previously obtained from the same time period the fragments were analyzed using two different thermal methods 1 the in field zero field iz or the izzi version of the classical thellier and thellier method and 2 the triaxe protocol that involves high temperature magnetization measurements data were corrected for the anisotropy of thermoremanent magnetization trm and the dependence of trm acquisition on the cooling rate was taken into account in the different protocols archeointensity data obtained on twin specimens sampled from the same fragment and using both experimental techniques generally show a good agreement i e within 5 at the fragment and at the site level all retained site level averaged intensity results 43 of 45 groups have standard deviations of less than 5 t furthermore groups of approximately the same age have very consistent archeointensity altogether the data presented herein recover a detailed and smoothed geomagnetic field intensity variation curve characterized by two peaks in intensity the first during the second half of the xivth century and the second around ad 1600 followed by a significant decreasing trend in intensity during most the xviith and xviiith centuries this evolution does not satisfactorily fit with the expected intensity values for france derived from geomagnetic field models relying on a different evolution of the axial dipole moment our results lead us to propose that the axial dipole moment decreased from ad 1600 to the end of the xviiith century then slightly increased up to ad 1850 before decreasing again to present day

geomagnetic field intensity how high can it get how fast can it change constraints from iron age copper slag article the intensity of the geomagnetic field varies over different time scales yet constraints on the maximum intensity of the field as well as for its maximum rate of change are inadequate due to poor temporal resolution and large uncertainties in the geomagnetic record the purpose of this study is to place firm limits on these fundamental properties by constructing a high resolution archaeointensity record of the levant from the 11th century to the early 9th century bce a period over which the geomagnetic field reached its maximum intensity in eurasia over the past 50 000 years we investigate a 14 c dated sequence of ten layers of slag material which accumulated within an ancient industrial waste mound of an iron age copper smelting site in southern israel depositional stratigraphy constrains relative ages of samples analyzed for paleointensity and 14 c dates from different horizons of the mound constrain the age of the whole sequence the analysis yielded 35 paleointenisty data points with accuracy better than 94 and precision better than 6 covering a period of less than 350 years most probably 200 years we construct a new high resolution quasi continuous archaeointensity curve of the levant that displays two dramatic spikes in geomagnetic intensity each corresponding to virtual axial dipole moment vadm in excess of 200 zam 2

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