a geodynamic model of mantle density heterogeneity using cenozoic and mesozoic plate motion reconstructions we derive a model of present day mantle density heterogeneity under the assumption that subducted slabs sink vertically into the mantle the thermal buoyancy of these slabs is estimated from the observed thermal subsidence cooling of oceanic lithosphere slab velocities in the upper mantle are computed from the local convergence rate we assume that slabs cross the upper lower mantle interface and continue sinking into the lower mantle with a reduced velocity for a velocity reduction factor between 2 and 5 our slab heterogeneity model is as correlated with current tomographic models as these models are correlated with each other we have also computed a synthetic geoid from our density model for a viscosity increase of about a factor of 40 from the upper to lower mantle our model predicts the first 8 spherical harmonic degrees of the geoid with statistical confidence larger than 95 and explains 84 of the observed geoid assuming that the model c21 and s21 terms are absent due to a long relaxation time for earth s rotational bulge otherwise 73 of the geoid variance is explained the viscosity increase is consistent with our velocity reduction factor for slabs entering the lower mantle since downwelling velocities are expected to scale roughly as the logarithm of viscosity loge 40 3 7 these results show that the history of plate tectonics can explain the main features of the present day structure of the mantle the dynamic topography induced by this heterogeneity structure consists mainly of about 1 km amplitude lows concentrated along the active continental margins of the pacific basin our model can also be used to predict the time variation of mantle heterogeneity and the gravity field we find that the age of the geoid defined as the time in the past before which the geoid becomes uncorrelated with the present geoid is about 50 m y our model for the history of the degree 2 geoid which is equivalent to the history of the inertia tensor should give us a tool to study the variations in earth s rotation pole indicated in paleomagiietic studies

itrf2008 plate motion model 1 the itrf2008 velocity field is demonstrated to be of higher quality and more precise than past itrf solutions we estimated an absolute tectonic plate motion model made up of 14 major plates using velocities of 206 sites of high geodetic quality far from plate boundaries deformation zones and glacial isostatic adjustment gia regions derived from and consistent with itrf2008 the precision of the estimated model is evaluated to be at the level of 0 3 mm a wrms no gia corrections were applied to site velocities prior to estimating plate rotation poles as our selected sites are outside the fennoscandia regions where the gia models we tested are performing reasonably well and far from gia areas where the models would degrade the fit antarctica and north america our selected velocity field has small origin rate bias components following the three axis x y z respectively 0 41 0 54 0 22 0 64 and 0 41 0 60 95 per cent confidence limits comparing our model to nnr nuvel 1a and the newly available nnr morvel56 we found better agreement with nnr morvel56 than with nnr nuvel 1a for all plates except for australia where we observe an average residual rotation rate of 4 mm a using our selection of sites we found large global x rotation rates between the two models 0 016 ma and between our model and nnr morvel56 of 0 023 ma equivalent to 2 5 mm a at the earth surface

new inferences of mantle viscosity from joint inversion of long wavelength mantle convection and post glacial rebound data we perform joint inversions for mantle viscosity of geophysical observables associated with both mantle convection and glacial isostatic adjustment gia our data include coefficients of the non hydrostatic geoid up to degree 8 and decay times associated with post glacial relative sea level rsl variations in hudson bay and fennoscandia we find that both data sets may be reconciled using a single profile of mantle viscosity which is characterized by a significant increase with depth across this region this result weakens previous arguments that the mantle rheology has significant transient effects the viscosity profiles we obtain are found to reconcile the observed free air gravity anomaly over hudson bay

on secular geocenter motion the impact of climate changes abstract we investigate the impact of recent climate changes on the long term displacement of the center of figure cf of the earth also defined as the geocenter in our convention with respect to the center of mass of the whole earth cm the two realizations of the international terrestrial reference system itrs entitled itrf2000 and itrf2005 present a difference of 1 8 mm yr between the velocities of their respective frame origins suggesting an acceleration of the geocenter towards the north pole we investigate if such a displacement could be explained by geophysical phenomena such as the present ice melting and the sea level rise using published observations on ice caps and glaciers we calculated the range of geocenter motion that may occur today we found that the global ice melting induces long term displacements of the geocenter mainly along the z axis toward the north pole the geocenter velocity is today between 0 3 and 0 7 0 8 mm yr and has doubled during last decade with the recent acceleration of ice melting combining with greff lefftz 2000 results on post glacial rebound we conclude that a present secular geocenter velocity of 1 mm yr is possible however the recent increase of the geocenter velocity cannot explain the difference observed between the two last realizations of the itrs our results comfort the previous conclusions about itrf2000 and itrf2005 and the pre analysis of itrf2008 data suggesting that the large z translation rate between the itrs realizations is probably due to an imprecise itrf2000 origin finally we show that determining precisely the geocenter velocity would give a new type of information that may be useful to more precisely constrain mass exchanges associated with climate changes

itrf2008 contribution to glacial isostatic adjustment and recent ice melting assessment 1 we investigate what information station vertical velocities of the itrf2008 provide on global geodetic parameters and by extension on glacial isostatic adjustment gia and recent ice melting rim processes we infer degree 2 spherical harmonic coefficients shc of the earth figure change and thej2 gravity rate j 2 which we compare with five gia models we find j 2 to be 0 0 2 4 10 11 yr 1 which is consistent with recent studies that propose a j 2 change in the 1990s due to rim whose contribution to the j 2 would be today around 3 5 4 0 2 4 10 11 yr 1 such results favor peltier 2004 vm2 or paulson et al 2007 gia models the itrf2008 shc that are directly impacted by the gia rotational feedback confirm with a good precision recent results from grace mission that initiated a debate on gia rotational feedback and about peltier gia model quality we find a coefficient consistent with paulson s and other model and more than 7 times smaller than coefficients in peltier s models two explanations are possible 1 if the model of peltier 2004 vm2 were to be correct then the strong rotational feedback in the model must be counteracted by a strong rotational feedback in the opposite direction generated by current ice loss 2 if the model of paulson et al 2007 were to be correct therefore gia and rim separately induce negligible rotational feedbacks both answers are quite extreme and call for more investigation on gia modeling and rotational feedback

the rotational stability of an ice age earth summary predictions of glaciation induced changes in the earth s rotation vector exhibit sensitivities to earth structure that are unique within the suite of long wavelength observables associated with glacial isostatic adjustment henceforth gia and despite nearly a quarter of a century of research these sensitivities remain enigmatic previous predictions of present day true polar wander tpw speed driven by gia have indicated for example a strong sensitivity to variations in the thickness of the elastic lithosphere and the treatment phase or chemical of the density discontinuity at 670 km depth nakada recently presented results that suggest that the predictions are also sensitive to the adopted rheology of the lithosphere however his results have introduced an intriguing paradox in particular predictions generated using a model with an extremely high viscosity lithospheric lid do not converge to results for a purely elastic lithosphere of the same thickness mitrovica as cited by nakada has suggested that the paradox originates from an inaccuracy in the traditional rotation theory e g wu peltier associated with the treatment of the background equilibrium rotating form upon which any load and rotation induced perturbations are superimposed we revisit these issues using a new treatment of the linearized euler equations governing load induced rotation perturbations on viscoelastic earth models we demonstrate that our revised theory in which the background form of the planet combines a hydrostatic component and an observationally inferred excess ellipticity resolves the apparent paradox calculations using the revised theory indicate that earlier predictions based on earth models with purely elastic lithospheric lids are subject to large errors indeed previously noted sensitivities of tpw speed predictions to the thickness and rheology elastic versus viscous of the lithosphere largely disappear in the application of the new theory significant errors are also incurred by neglecting the stabilizing influence of the earth s excess ellipticity finally we demonstrate that the contribution from rotational feedback on predictions of present day rates of change of the geoid sea surface and crustal velocities are overestimated by the traditional rotation theory and this has implications for analyses of ongoing satellite e g grace missions and geodetic gps surveys

a complete formalism for the inversion of post glacial rebound data resolving power analysis summary a formal inverse theory for mantle viscosity based upon the data of glacial isostatic adjustment is here formulated and applied to synthetic data in this theory full account has been taken of the normal mode nature of the forward problem for realistic viscoelastic maxwell models of the planet since it is impossible to accurately infer the excitation and decay constants of the individual normal modes from the observations the formalism is cast in terms of the observed gross earth data in the time domain in this analysis expressions are required for the first order perturbations in both the modal amplitudes and relaxation times that are induced by an arbitrary radial perturbation to the starting viscosity profile a numerical technique is developed which enables us to accurately determine differential kernels for the modal amplitudes the analogous kernels for the modal decay times are derived analytically peltier 1976 and the complete set of kernels is shown to satisfy the physical constraint imposed by the uniqueness of the state of isostatic equilibrium for the viscously incompressible maxwell models that we employ when the problem is parametrized in terms of the logarithm of viscosity the kernels are capable of accurately predicting shifts in the normal mode characteristics for at least an order of magnitude variation in mantle viscosity using bayesian statistics a formal inversion is applied to a set of synthetically generated data these data chosen to reproduce the space time coverage of the actual observables include a subset related to the global gravity field and a large sequence of idealized relative sea level rsl curves it is found that even very weak a priori constraints can provide a stable and accurate inversion a resolving power analysis indicates a spatial resolution of approximately 1200km near the core mantle boundary cmb with a gradual improvement to better than 350km in the middle of the upper mantle subsets of the synthetic data are inverted in order to examine conditions on stability and accuracy and to determine their relative contributions to the spatial resolution data from progressively older beaches are shown to contribute most to the spatial resolution at all depths though the improvement in lower mantle resolution converges for data obtained from beaches formed within the last 5000 yr furthermore the rsl curves in the vicinity of the peripheral bulge of the ancient laurentide ice sheet are significant contributors to lower mantle resolution as demonstrated in previous analyses of the forward problem the inversion of this subset of the data also appears to be encouragingly stable

convective patterns under the indo atlantic box using fluid mechanics we reinterpret the mantle images obtained from global and regional tomography together with geochemical geological and paleomagnetic observations and attempt to unravel the pattern of convection in the indo atlantic box and its temporal evolution over the last 260 myr the box presently contains a a broad slow seismic anomaly at the cmb which has a shape similar to pangea 250 myr ago and which divides into several branches higher in the lower mantle b a superswell centered on the western edge of south africa c at least 6 primary hotspots with long tracks related to traps and d numerous smaller hotspots in the last 260 myr this mantle box has undergone 10 trap events 7 of them related to continental breakup several of these past events are spatially correlated with present day seismic anomalies and or upwellings laboratory experiments show that superswells long lived hotspot tracks and traps may represent three evolutionary stages of the same phenomenon i e episodic destabilization of a hot chemically heterogeneous thermal boundary layer close to the bottom of the mantle when scaled to the earth s mantle its recurrence time is on the order of 100 200 myr at any given time the indo atlantic box should contain 3 to 9 of these instabilities at different stages of their development in agreement with observations the return flow of the downwelling slabs although confined to two main boxes indo atlantic and pacific by subduction zone geometry may therefore not be passive but rather take the form of active thermochemical instabilities

observed and numerically simulated structure of a mature supercell thunderstorm abstract through the interactive use of doppler radar analyses and a three dimensional numerical storm simulation the detailed structure of a supercell tornadic storm is analyzed this storm named the del city storm occurred in central oklahoma on 20 may 1977 the storm exhibits certain important features which are essential to maintaining its longevity and which promote the storm s transition to its tornadic phase these features are strongly influenced by the rotational character of the storm separates the precipitation from the updraft and which orients the resulting downdrafts to which reinforce low level convergence along the gust front and sustain the storm analyses of air parcel and rain trajectories within the storm provide a detailed visualization of this internal structure these trajectories reveal that air parcels rising through the cyclonically rotating updraft actually turn anticyclonically with height owing to the influence of the storm relative environmental wind field downdraft traj

thermal and chemical heterogeneity in the mantle a seismic and geodynamic study of continental roots abstract chemical differences in the mantle below continents and oceans are investigated in the context of a recent seismic model of three dimensional mantle structure this analysis of the existence and magnitude of deep continent ocean chemical differences is based on a model of a viscous flowing mantle and it suggests that this continent ocean heterogeneity is internally supported and thus produces little flow this stabilization reduces the vertical flow of mass and heat across the upper mantle and results in a large continent ocean signal in the surface gravity and topography fields the stabilization of continent ocean heterogeneity also provides an explanation for the large amplitude of the nonhydrostatic ellipticity in the earth s geoid

grace gravity observations constrain weichselian ice thickness in the barents sea the barents sea is subject to ongoing postglacial uplift since the melting of the weichselian ice sheet that covered it the regional ice sheet thickness history is not well known because there is only data at the periphery due to the locations of franz joseph land svalbard and novaya zemlya surrounding this paleo ice sheet we show that the linear trend in the gravity rate derived from a decade of observations from the gravity recovery and climate experiment grace satellite mission can constrain the volume of the ice sheet after correcting for current ice melt hydrology and far field gravitational effects regional ice loading models based on new geologically inferred ice margin chronologies show a significantly better fit to the grace data than that of ice 5g the regional ice models contain less ice in the barents sea than present in ice 5g 5 6 3 m equivalent sea level versus 8 5 m which increases the ongoing difficulty in closing the global sea level budget at the last glacial maximum

recent earth oblateness variations unraveling climate and postglacial rebound effects earth9s dynamic oblateness j2 has been decreasing due to postglacial rebound pgr however j2 began to increase in 1997 indicating a pronounced global scale mass redistribution within earth9s system we have determined that the observed increases in j2 are caused primarily by a recent surge in subpolar glacial melting and by mass shifts in the southern pacific and indian oceans when these effects are removed the residual trend in j2 2 9 x 10 11 year 1 becomes consistent with previous estimates of pgr from satellite and eclipse data the climatic significance of these rapid shifts in glacial and oceanic mass however remains to be investigated

plasmaspheric drainage plume observed by the polar satellite in the prenoon sector and the image satellite during the magnetic storm of 11 april 2001 1 during the early main phase of a geomagnetic storm on 11 april 2001 the polar satellite was inside the magnetosphere in the prenoon sector 1000 1100 magnetic local times and experienced a magnetopause crossing at l 6 because of the high solar wind dynamic pressure and strong southward interplanetary magnetic field imf just before the magnetopause crossing polar observed cold dense plasma that is the cold dense plasma was immediately adjacent to the compressed magnetopause using simultaneous observations by the image extreme ultraviolet euv imager we confirm that the cold dense plasma observed by polar is a plasmaspheric drainage plume extending outward from the plasmasphere to the magnetopause during the interval of high geomagnetic activity and strong southward imf we compare plasmaspheric mass densities determined from ground magnetometer data at l 2 3 and 2 9 for a magnetically quiet time interval to mass densities determined during the magnetic storm time interval we find no significant differences in the mass density between both intervals these observations suggest that the sunward convecting plasmaspheric plasma observed at polar is due to erosion of the outer layers of the plasmasphere beyond l 2 9

length of day variations due to mantle dynamics at geological timescale summary the geological evolution of length of day lod variations is mainly controlled by the frictional tidal torque responsible for the secular slowdown of the earth s rotation and for the receding of the moon superimposed on this variation which has existed since the early history of the planet there are at shorter timescales less than 1 myr lod perturbations induced by the glaciation deglaciation cycles in this paper we investigate the influence of mantle dynamics on lod at the geological timescale we use the complete non linear equations to compute the influence of mantle density heterogeneities on the angular velocity of the rotation that is to say on the lod we discuss the degree zero coefficient of the spherical harmonic expansion of the mantle mass anomaly which is strongly dependent on the conservation of mass of the earth we first compute the effects induced by upwelling domes and subducted plates sinking into the mantle which are known to induce geological variations in the orientation of the rotation axis with respect to a fixed terrestrial frame the so called true polar wander we find that the time variable mantle density heterogeneities associated with the large scale pattern of plate tectonic motions since 120 ma and with the upwelling domes can perturb lod by about per year that is with an order of magnitude smaller than the effects induced by the last deglaciation superimposed on this linear trend we show that there are fluctuations around 0 1 0 2 s myr 1 on a timescale of a few tens of millions of years we then combine a spherical model of mantle circulation with solutions for the equations governing the rotation of a viscous planet to improve the constraint of mantle mass conservation finally we compare our results with other effects

dynamic mantle density heterogeneities and global geodetic observables summary we investigate the influence of mantle dynamics on low degree deformations of the earth at geological timescale we first compute surface deformations and discuss the analytical form of the tangential surface displacement induced by internal loads in a reference frame related to the centre of mass of the planet we use the theoretical love numbers formalism since the earth has a viscoelastic behaviour at geological timescale then we quantify degree one and degree two deformations induced by upwelling domes and subducted plates sinking into the mantle we use a simple model in which the slabs are modelled as blobs diving vertically through the mantle and in which the domes are assumed to be stable over the last 120 ma their location is modelled from seismic tomography within the lower mantle the temporal evolutions of the j2 gravitational potential coefficient and of the geocentre motion are plotted since 120 ma we find that 1 the mantle density heterogeneities within the mantle can explain the present day non hydrostatic flattening of the earth however they vary at a too slow timescale to significantly perturb the coefficient 2 although there is a significant discrepancy of about a few hundred metres between the centre of figure and the centre of mass of the earth the secular variation of the geocentre motion is one order of magnitude smaller than the one induced by surface loads

vortex lines within low level mesocyclones obtained from pseudo dual doppler radar observations abstract vortex lines passing through the low level mesocyclone regions of six supercell thunderstorms three nontornadic three tornadic are computed from pseudo dual doppler airborne radar observations obtained during the verification of the origins of rotation in tornadoes experiment vortex in every case at least some of the vortex lines emanating from the low level mesocyclones form arches that is they extend vertically from the cyclonic vorticity maximum then turn horizontally usually toward the south or southwest and descend into a broad region of anticyclonic vertical vorticity this region of anticyclonic vorticity is the same one that has been observed almost invariably to accompany the cyclonic vorticity maximum associated with the low level mesocyclone the vorticity couplet straddles the hook echo of the supercell thunderstorm the arching of the vortex lines and the orientation of the vorticity vector along the vortex line arches compared to the orientation of the ambient barotrop

a study of the tornadic region within a supercell thunderstorm abstract the transition of a supercell thunderstorm into its tornadic phase is investigated through high resolution numerical cloud model simulations initiated within the interior portion of a previously simulated mature supercell storm with the enhanced grid resolution the low level cyclonic vorticity increases dramatically and the gust front rapidly occludes as small scale downdrafts develop in the vicinity of the low level center of circulation as the occlusion progresses a ring of high vorticity air surrounds the circulation center and could be conducive to multiple vortex tornado formation numerous features of the simulated transition bear resemblance to those observed in tornadic storms in the model simulation the large low level vorticity is generated through the tilting and intense stretching of air from the inflow side of the storm this vertical vorticity is derived from the horizontal vorticity of the environmental shear and also from horizontal vorticity generated solenoidally as low l

effect of plasmaspheric drainage plumes on solar wind magnetosphere coupling evidence is uncovered that plasmaspheric drainage plumes flowing into the dayside reconnection site mass load the reconnection rate and thereby reduce the coupling of the solar wind to the earth s magnetosphere solar wind magnetosphere coupling is statistically analyzed with the 1963 2003 omni2 data set matched up with the ae au and pci geomagnetic indices times when plasmaspheric drainage plumes are flowing are discerned using multiple spacecraft with plasma detectors in geosynchronous orbit it is found that for a given value of vbz of the solar wind the geomagnetic indices ae au and pci are statistically lower when plasmaspheric drainage plumes are present than when plumes are not present this is taken as a measure of a weakened coupling of the solar wind to the earth s magnetosphere caused by the plumes an addendum examines the effects of polar cap saturation on the auroral electrojet index

slabs in the lower mantle results of dynamic modelling compared with tomographic images and the geoid abstract the recent increase in resolution of tomographic images of the earth s interior has enabled us to see slabs in the lower mantle on the other hand the distribution of slabs can be inferred from subduction history using a dynamical model of mantle flow comparison of tomographic images with model results can help to distinguish between alternative models of subduction history tomographic models and mantle flow models and thus improve our understanding of the earth here a simple dynamic model of subduction is used and some results are presented amounts and locations of subduction are inferred from published models of plate motion and plate boundaries for the past 120 ma the latter have been interpolated on 2 ma time intervals mantle flow driven by the density anomalies corresponding to subducted slabs is calculated with the method of hager and o connell for a viscosity structure that features an increase in viscosity from 4 10 20 pa below the lithosphere to 4 10 22 pa in the lower part of the lower mantle slabs are advected in the flow field in the model slabs sink on average about 1700 km through the mantle during 100 ma however the calculated average horizontal motion of slabs throughout most of the mantle is only about 600 700 km for slabs that have sunk to the lowermost mantle it is about 1000 km this is in accordance with the previously observed good correlation between subduction locations and lowermost mantle heterogeneities slabs sink fastest in regions with abundant subduction and little trench migration e g below east asia in the lowermost mantle predicted slab locations tend to lie in areas with high seismic velocities however there are large areas of fast seismic velocities where no slabs are predicted and which therefore presumably correspond to earlier subduction in some regions e g below japan our model approximately reproduces the observed shape of the slab in other regions where the agreement is poor the results can help to further constrain models of subduction history and associated mantle flow additionally the predicted geoid is computed and compared with the actual geoid predicted and observed geoid have similar magnitude and a number of features in common however an optimization of the fit is not attempted here since in order to do this also the hot upwellings from the lower boundary layer presumably in the form of plumes would have to be included

secular variation of the geocenter the degree 1 deformations of earth induced by a surface load are computed in a reference frame related to the center of mass of the planet using a theoretical approach love number formalism at secular timescale where earth has a viscoelastic behavior the temporal variation of the coordinates of the geocenter induced by the pleistocenic deglaciation is investigated for two loading histories three ice sheets with the same time dependence or ice 3g model testing different viscosity profiles within the mantle the present day secular variation of earth s geocenter induced by postglacial rebound is found to be from 0 2 up to 0 5 mm yr and consequently we suggest that observations from space geodesy of this rate could be used to constrain the viscosity contrast between upper and lower mantle

mantle viscosity inferences from joint inversions of pleistocene deglaciatio induced changes in geopotential with a new slr analysis and polar wander joint inversions of post glacial rebound induced secular changes in low degree harmonics of the geopotential and true polar wander tpw systematically indicate that the upper mantle viscosity has a value that is considerably smaller than 10 21 pas the lower mantle viscosity is about one order of magnitude larger than the upper mantle viscosity discrepancies in the viscosity profiles inferred from even and odd zonals are likely an indication of recent unmodeled glacial forcings and or insufficient precision in the evaluation of the mass loss from pleistocene ice sheets the influence of systematic errors in slr data reduction due to thermal drag on the lageos satellites for the uneven zonals of the geopotential is avoided by making use of the starlette and stella satellites to recover the uneven zonals and by considering lumped coefficients for these uneven terms

the inference of mantle viscosity from an inversion of the fennoscandian relaxation spectrum summary a formal inverse theory for mantle viscosity is here applied to a relaxation spectrum derived from the post glacial uplift of fennoscandia the spectrum represents the set of eigenfrequencies or inverse decay times for the fundamental mode of viscous gravitational relaxation between the spherical harmonic degrees 14 to 45 and 65 to 80 theoretical predictions of the eigenfrequencies are based upon the determination of the zeroes of the secular determinant function derived for a spherically symmetric self gravitating visco elastic planet differential kernels relating shifts in the eigenfrequencies to arbitrary perturbations in the radial viscosity profile i e frechet kernels are computed using the variational principle derived by peltier 1976 the inversions are performed within the framework of non linear bayesian inference and the problem has been parameterized in terms of the logarithm of viscosity the inversions have yielded a set of robust constraints which all models for the radial viscosity profile below fennoscandia must satisfy the a posteriori estimates and variance reduction are found to be insensitive to the a priori variance ascribed to the model layers the constraints have furthermore been summarized into a set of a posteriori estimates of the average model viscosity value in radial regions consistent with the resolving power of the data which decreases from a radial length scale of approximately 120km at the base of the lithosphere to 1200km at 1000km depth the data provide essentially no information regarding the mantle rheology below 1200km depth for example for earth models with a lithospheric thickness lt of 100 km the volumetric average logarithm of viscosity in regions in the depth ranges 1040 400 km 670 210 km and 235 100 km is constrained to be respectively 21 03 0 09 20 70 0 08 and 20 37 0 19 we have repeated the inversions for a number of assumed lithospheric thicknesses and have found that a relatively low viscosity layer in the sublithospheric region with respect to the underlying upper mantle is required for lt 120km in this respect we have quantified the previously described trade off between a decrease in the viscosity of this region and a decrease in lt cathles 1975 in forward analyses of the glacial isostatic adjustment data set it is common to use earth models with isoviscous upper and lower mantle regions to investigate this two layer case we have also performed inversions which assume perfect correlation amongst the model layers in the upper and separately the lower mantle under this strict model space limitation the inversions yield models with upper and lower mantle viscosities in the range 3 7 1020 4 5 1020 pa s and 2 2 1021 1 9 1021 pa s respectively the ranges are obtained from a suite of inversions using lithospheric thickness from 70 km to 145 km the a posteriori constraints generated from the bayesian inversions are used together with a statistic based on the computed misfit to the fennoscandian relaxation spectrum to rule out a number of previously published viscosity models

geophysical interpretation of observed geocenter variations geocenter variations are caused by mass redistribution within the earth system especially the atmosphere oceans and continental water using surface pressure fields and soil moisture and snow depth fields of the ncep ncar climate data assimilation system i cdas i 1 we estimate contributions from variations in atmospheric surface pressure and continental water storage to the earth s geocenter center of mass variation in addition sea surface anomalies determined by the topex poseidon altimeter are used to investigate geocenter variations resulting from ocean mass redistribution these sea surface height data were corrected using a simplified steric model a comparison with observed geocenter variations derived from lageos 1 and 2 satellite laser ranging data indicates that the atmosphere oceans and continental hydrological cycle all provide significant contributions at different frequencies geocenter variations estimated in this paper are in reasonably good agreement with results given by dong et al 1997 for atmospheric and ocean contributions but not for the estimates of continental hydrological contributions

joint analysis of goce gravity gradients data of gravitational potential and of gravity with seismological and geodynamic observations to infer mantle properties joint analysis of the seismic velocities and geoid gravity and gravity gradients are used to constrain the viscosity profile within the mantle as well as the lateral density variations recent esa s gravity field and steady state ocean circulation explorer measurements of the second order derivatives of the earth s gravity potential give new possibilities to determine these mantle properties using a simple mantle model and seismic tomography results we investigate how the gravitational potential the three components of the gravity vector and the gravity gradients can bring information on the radial viscosity profile and on the mantle mass anomalies we start with lateral density variations in the earth s mantle based either on slab history or deduced from seismic tomography the main uncertainties are for the latter case the relationship between seismic velocity and density the so called density velocity scaling factor and for the former case the variation with depth of the density contrast between the cold slabs and the surrounding mantle we perform a monte carlo search for the viscosity and the density velocity scaling factor profiles within the mantle which allows to fit the observed geoid gravity and gradients of gravity we compute the posterior probability distribution of the unknown parameters and find that the gravity gradients improve the estimate of the scaling factor within the upper mantle because of their sensitivity to the masses within the upper mantle whereas the geoid and the gravity better constrain the scaling factor in the lower mantle in the upper mantle it is less than 0 02 in the upper part and about 0 08 0 14 in the lower part and it is significantly larger for depths greater than 1200 km about 0 32 0 34 in any case the density velocity scaling factor between 670 and 1150 km depth is not well constrained we show that the viscosity of the upper part of the mantle is strongly correlated with the viscosity of the lower part of the mantle and that the viscosity profile is characterized by a decrease in the lower part of the upper mantle about 10 20 2 10 20 pa s and by an increase about 10 23 2 10 23 pa s at the top of the lower mantle between 670 and 1150 km

boundary layer structure and dynamics in outer hurricane rainbands part i mesoscale rainfall and kinematic structure abstract results of hurricane boundary layer experiments conducted in outer rainbands of hurricanes josephine 1984 and earl 1986 are presented comparisons of precipitation and kinematic structures in these storms and in hurricane floyd 1981 indicate that principal rainbands have common characteristic mesoscale and convective scale features in the boundary layer the two dimensional mesoscale structure suggests that these rainbands are made up of a linear aggregate of cellular reflectivity elements on the inner upshear side of the band and stratiform rain on the outer downshear side the bands are oriented perpendicular to the shear above the boundary layer and cells move downband at about 85 of the density weighted mean wind speed of the 0 2 6 km layer the boundary layer wind field is strongly influenced by the rainband with alongband and crossband wind maxima located on the outer side of the band axis and minima 4 8 km to the inner side maximum crossband convergence and cyclonic shear vor

direct observations of the role of convection electric field in the formation of a polar tongue of ionization from storm enhanced density 1 we examine the relationship of convection electric fields to the formation of a polar cap tongue of ionization toi from midlatitude plumes of storm enhanced density sed observations from the geomagnetic storm on 26 27 september 2011 are presented for two distinct sed events during an hour long period of geomagnetic activity driven by a coronal mass ejection a channel of high density f region plasma was transported from the dayside subauroral ionosphere and into the polar cap by enhanced convection electric fields extending to middle latitudes this toi feature was associated with enhanced hf backscatter indicating that it was the seat of active formation of small scale irregularities after the solar wind interplanetary magnetic field conditions quieted and the dayside convection electric fields retreated to higher latitudes an sed plume was observed extending to but not entering the dayside cusp region this prominent feature in the distribution of total electron content tec persisted for several hours and elongated in magnetic local time with the rotation of the earth no ionospheric scatter from superdarn radars was observed within this sed region the source mechanism enhanced electric fields previously drawing the plasma from midlatitudes and into the polar cap as a toi was no longer active resulting in a fossil feature we thus demonstrate the controlling role exercised by the convection electric field in generating a toi from midlatitude sed

enceladus s and dione s floating ice shells supported by minimum stress isostasy enceladus gravity and shape have been explained in terms of a thick isostatic ice shell floating on a global ocean in contradiction of the thin shell implied by librations here we propose a new isostatic model minimizing crustal deviatoric stress and demonstrate that gravity and shape data predict a 38 4km thick ocean beneath a 23 4km thick shell agreeing with but independent from libration data isostatic and tidal stresses are comparable in magnitude south polar crust is only 7 4km thick facilitating the opening of water conduits and enhancing tidal dissipation through stress concentration enceladus resonant companion dione is in a similar state of minimum stress isostasy its gravity and shape can be explained in terms of a 99 23km thick isostatic shell overlying a 65 30km thick global ocean thus providing the first clear evidence for a present day ocean within dione

total meltwater volume since the last glacial maximum and viscosity structure of earth s mantle inferred from relative sea level changes at barbados and bonaparte gulf and gia induced j2

the lageos constraint on deep mantle viscosity results from a new normal mode method for the inversion of viscoelastic relaxation spectra the recently observed acceleration in the node of the orbit of the lageos satellite has previously been shown to provide a good constraint on the viscosity of the earth s mantle beneath the 670 km seismic discontinuity this paper explores the extent to which the previously inferred lower mantle viscosity may be traded off against variations of other properties of the radial viscoelastic structure we show explicitly that the nontidal acceleration of rotation inferred from the lageos data and predicted as a consequence of the earth s response to the last deglaciation event of the current ice age is relatively insensitive both to variations of lithospheric thickness and to the presence or absence of plausible chemical heterogeneity across the 670 km interface it therefore provides a high quality constraint on the viscosity of the deep mantle with the upper mantle viscosity fixed at the nominal value of 1021 pa s the bounds on lower mantle viscosity lm are such that 2 1021 pa s lm 6 1021 pa s even when allowance is made for the presence of a viscous boundary layer at the base of the upper mantle such as would exist if the mantle convective circulation were layered

global plasmasphere evolution 22 23 april 2001 1 the evolution of the plasmasphere during the moderate 22 23 april 2001 storm is studied by comparing observed plasmasphere behavior to the predictions of a simulation the plasmasphere observations include global images from image euv and density and flow measurements from lanl mpa the subjective uncertainty in the euv plasmapause was found to be 0 2l inward plasmapause motion was correlated with southward interplanetary magnetic field imf with a 27 min delay the electric e field at the plasmapause was approximately 13 of the solar wind e field the observations support the idea that plasmaspheric erosion begins with a partial plasmapause indentation which then gradually widens in magnetic local time mlt to encompass the entire nightside in situ measurements confirm a dayside plume of sunward flowing plasma and images show that the plume subsequently experienced phases of mlt narrowing and rotation wrapping to simulate the event we employed a test particle representation of the plasmapause using a parametric e field model that includes corotation and convection from two sources dayside magnetopause reconnection dmr and the subauroral polarization stream saps the model captures the phases of plume evolution and it reproduces the observed plasmapause with maximum mean error 0 7l 0 24l the model fails to reproduce important subglobal features e g a predawn plasmaspheric shoulder and grossly misplaces the inner edge of the rotating and wrapping plume saps contributes significantly to the duskside flows but the simulated flows are about 50 smaller than those seen by lanl mpa the simulated plasmapause e field is about 70 of the euv inferred value

detection of a large scale mass redistribution in the terrestrial system since 1998 earth9s dynamic oblateness j2 had been undergoing a decrease according to space geodetic observations over the past 25 years until around 1998 when it switched quite suddenly to an increasing trend that has continued to the present the secular decrease in j2 resulted primarily from the postglacial rebound in the mantle the present increase whose geophysical cause s are uncertain thus signifies a large change in global mass distribution with a j2 effect that considerably overshadows that of mantle rebound

itrf2005 a new release of the international terrestrial reference frame based on time series of station positions and earth orientation parameters 1 unlike the past international terrestrial reference frame itrf versions where global long term solutions were combined the itrf2005 uses as input data time series weekly from satellite techniques and 24 h session wise from very long baseline interferometry of station positions and daily earth orientation parameters eops the advantage of using time series of station positions is that it allows to monitor station non linear motion and discontinuities and to examine the temporal behavior of the frame physical parameters namely the origin and the scale the itrf2005 origin is defined in such a way that it has zero translations and translation rates with respect to the earth center of mass averaged by the satellite laser ranging slr time series spanning 13 years of observations its scale is defined by nullifying the scale and its rate with respect to the very long baseline interferometry vlbi time series spanning 26 years of observations the itrf2005 orientation at epoch 2000 0 and its rate are aligned to the itrf2000 using 70 stations of high geodetic quality the estimated level of consistency of the itrf2005 origin at epoch 2000 0 and its rate with respect to the itrf2000 is respectively 0 1 0 8 5 8 mm and 0 2 0 1 1 8 mm yr along the x yand z axis we estimate the formal errors on these components to be 0 3 mm and 0 3 mm yr we believe that this low level of agreement between the two frame origins is most probably due to the poor slr network geometry and its degradation over time the itrf2005 combination involving 84 co location sites revealed a scale inconsistency of 1 ppb 6 3 mm at the equator at epoch 2000 0 and 0 08 ppb yr between the slr and vlbi long term solutions as obtained by the stacking of their respective time series possible causes of this inconsistency may include the poor slr and vlbi networks and their co locations local tie uncertainties systematic effects and possible inconsistent model corrections used in the data analysis of both techniques for the first time of the itrf history the itrf2005 rigorous combination provides self consistent series of eops including polar motion from vlbi and satellite techniques and universal time and length of day from vlbi only a velocity field of 152 sites with an error less than 1 5 mm yr is used to estimate absolute rotation poles of 15 tectonic plates that are consistent with the itrf2005 frame this new absolute plate motion model supersedes and significantly improves that of the itrf2000 which involved six major tectonic plates citation altamimi z x collilieux j legrand b garayt and c boucher 2007 itrf2005 a new release of the international terrestrial reference frame based on time series of station positions and earth orientation parameters j geophys res 112 b09401

evidence for postglacial signatures in gravity gradients a clue in lower mantle viscosity abstract the earth s surface was depressed under the weight of ice during the last glaciations glacial isostatic adjustment gia induces the slow recession of the trough that is left after deglaciation and is responsible for a contemporary uplift rate of more than 1 cm yr around hudson bay the present day residual depression an indicator of still ongoing gia is difficult to identify in the observed topography which is predominantly sensitive to crustal heterogeneities according to the most widespread gia models which feature a viscosity of 2 3 10 21 pa s on top of the lower mantle the trough is approximately 100 m deep and cannot explain the observed gravity anomalies across north america these large anomalies are therefore usually attributed to subcontinental density heterogeneities in the tectosphere or to slab downwelling in the deep mantle here we use observed gravity gradients gg to show that the uncompensated gia trough is four times larger than expected and that it is the main source of the north american static gravity signal we search for the contribution to these ggs from mantle mass anomalies which are deduced from seismic tomography and are mechanically coupled to the global mantle flow this contribution is found to be small over laurentia and at least 82 of the ggs are caused by gia such a contribution from gia in these gg observations implies a viscosity that is greater than 10 22 pa s in the lower mantle our conclusions are a plea for gia models with a highly viscous lower mantle which confirm inferences from mantle dynamic models any change in gia modelling has important paleoclimatological and environmental implications encouraging scientists to re evaluate the past ice history at a global scale these implications in turn affect the contribution of bedrock uplift to the contemporaneous mass balance over antarctica and greenland and thus the present day ice melting rate as deduced from the grace space mission additionally studies of the thermo chemical structure of the lithosphere crust under north america that exploit gravity or geodetic data should be corrected for a gia model which is not the case today

mantle dynamics geoid inertia and tpw since 120 myr abstract we investigate the effect of internal masses redistributions on the position of the earth rotational pole for the last 120 myr we use a geodynamic model based on plate reconstructions that estimates the location and rate of subducted slabs under the assumption that they sink vertically into the mantle ricard et al 1993b our model also takes into account the effect of large scale upwellings domes derived from an analysis of seismic tomography their location is assumed to remain stable with time we then compute the geoid associated with the time dependent mantle density heterogeneities in order to reconcile the computed and observed geoids we investigate the influence of the depth down to which the subducted pacific plates beneath the americas present a significant density contrast with respect to the surrounding mantle on the present day geoid and propose a plate model in which we obtain a variance reduction greater than 0 9 for the degree 2 we show that the vertical oscillation of domes within mantle only modulates the amplitude of the associated geoid the temporal variation of the mantle density heterogeneities is consequently essentially due to changes in the subduction history the temporal evolution of the principal inertia axis pia of the earth derived from our model the rotational axis is aligned to the maximum pia is then investigated and finally compared to estimations of tpw both the maximum and intermediate pias have moved in a plane perpendicular to africa along a circle corresponding to the low of geoid induced by subduction around the pacific the minimum pia seems to be relatively stable since 120 myr and close to the maximum degree 2 geoid high under africa this can account for observed tpw or african apw in the last 200 myr

long lived plasmaspheric drainage plumes where does the plasma come from long lived weeks plasmaspheric drainage plumes are explored the long lived plumes occur during long lived high speed stream driven storms spacecraft in geosynchronous orbit see the plumes as dense plasmaspheric plasma advecting sunward toward the dayside magnetopause the older plumes have the same densities and local time widths as younger plumes and like younger plumes they are lumpy in density and they reside in a spatial gap in the electron plasma sheet in sort of a drainage corridor magnetospheric convection simulations indicate that drainage from a filled outer plasmasphere can only supply a plume for 1 5 2 days the question arises for long lived plumes and for any plume older than about 2 days where is the plasma coming from three candidate sources appear promising 1 substorm disruption of the nightside plasmasphere which may transport plasmaspheric plasma outward onto open drift orbits 2 radial transport of plasmaspheric plasma in velocity shear driven instabilities near the duskside plasmapause and 3 an anomalously high upflux of cold ionospheric protons from the tongue of ionization in the dayside ionosphere which may directly supply ionospheric plasma into the plume in the first two cases the plume is drainage of plasma from the magnetosphere in the third case it is not where the plasma in long lived plumes is coming from is a quandary to fix this dilemma further work and probably full scale simulations are needed

an explanation for earth s long term rotational stability paleomagnetic data show less than approximately 1000 kilometers of motion between the paleomagnetic and hotspot reference frames that is true polar wander during the past 100 million years which implies that earth s rotation axis has been very stable this long term rotational stability can be explained by the slow rate of change in the large scale pattern of plate tectonic motions during cenozoic and late mesozoic time provided that subducted lithosphere is a major component of the mantle density heterogeneity generated by convection therefore it is unnecessary to invoke other mechanisms such as sluggish readjustment of the rotational bulge to explain the observed low rate of true polar wander

ice 3g a new global model of late pleistocene deglaciation based upon geophysical predictions of post glacial relative sea level change a new high resolution global model of late pleistocene deglaciation is inferred on the basis of geophysical predictions of postglacial relative sea level variations in which the ice ocean solid earth interaction is treated in a gravitationally self consistent fashion for the purpose of these analyses the radial viscoelastic structure of the planet is assumed known on the basis of previously published sensitivity tests on solutions of the forward problem only radiocarbon controlled relative sea level histories from sites that were actually ice covered with one or two additions are employed to constrain the model leaving relative sea level rsl data from sites that were not ice covered to be employed to confirm its consistency results for these confirmatory analyses are reported elsewhere here the new deglaciation model referred to as ice 3g is compared to previous models derived by several independent means and tested against a number of additional observations other than sea level histories including geologically controlled retreat isochrones oxygen isotope data from deep sea sedimentary cores and coral terrace elevations the latter two observations strongly constrain the net sea level rise that has occurred since the onset of deglaciation and therefore the mass of ice that melted during the last glacial interglacial transition

hook echoes and rear flank downdrafts a review abstract nearly 50 years of observations of hook echoes and their associated rear flank downdrafts rfds are reviewed relevant theoretical and numerical simulation results also are discussed for over 20 years the hook echo and rfd have been hypothesized to be critical in the tornadogenesis process yet direct observations within hook echoes and rfds have been relatively scarce furthermore the role of the hook echo and rfd in tornadogenesis remains poorly understood despite many strong similarities between simulated and observed storms some possibly important observations within hook echoes and rfds have not been reproduced in three dimensional numerical models

numerical simulation of tornadogenesis in an outer rainband minisupercell of typhoon shanshan on 17 september 2006 abstract on 17 september 2006 three tornadoes occurred along the east coast of kyusyu island in western japan during the passage of an outer rainband in the right front quadrant of typhoon shanshan to clarify the structure of the tornado producing storms and the mechanism of tornadogenesis quadruply nested numerical simulations were performed using a nonhydrostatic model with an innermost horizontal grid spacing of 50 m several simulated convective storms in the outermost rainband exhibited characteristics of a minisupercell one storm had a strong rotating updraft of more than 30 m s 1 and a large vertical vorticity exceeding 0 06 s 1 this storm spawned a tornado when the low level mesocyclone intensified the tornado was generated on the rear flank gust front near the mesocyclone center when a secondary rear flank downdraft rfd surge advanced cyclonically around the low level mesocyclone and overtook the rear flank gust front at its left front edge backward trajectories and vorticity budget anal

global response of the plasmasphere to a geomagnetic disturbance 1 global images of the plasmasphere obtained by the extreme ultraviolet euv imager on the image satellite are used to study the evolving structure of the plasmasphere during two geomagnetic disturbances by tracking the location of the plasmapause as a function of l shell and magnetic local time quantitative measurements of radial and azimuthal motions of the boundary are made for intervals 7 hours in duration with a time resolution of 10 min the two cases presented are 26 27 june 2001 a relatively weak but isolated geomagnetic disturbance and 9 10 june 2001 a moderate event with a multistaged onset and recurring substorm activity after the main disturbance in both cases the onset of the disturbance correlated with a southward turning of the imf is characterized by inward motion or erosion of the plasmapause and a smoothing of any existing azimuthal variations across the nightside over a period of many hours a plasmaspheric plume forms in the afternoon sector as a result of sunward flows from dusk and corotational flows across the dayside azimuthal variations in the plasmapause radius tend to form in the local time sector from dawn to the western edge of the plume including mesoscale 0 5 in l and 2 hours in local time crenulations and larger scale shoulder features while the nightside boundary remains featureless in the 26 27 june 2001 case the magnetosphere entered a period of deep quiet after the main disturbance and the plasmaspheric plume began to corotate with the main plasmasphere from the afternoon sector across the nightside in contrast the plume in the 9 10 june 2001 event became wrapped around the main plasmasphere and a second plume formed in the afternoon sector perhaps due to continued substorm activity in situ density data for these events show highly irregular density structure within the plumes as measured at geosynchronous orbit whereas a measurement by image rpi suggests that there may be less structure near the base of the plume closer to the main plasmasphere

ionospheric signatures of plasmaspheric tails 1 we make direct comparisons between gps maps of total electron content tec over the north american continent millstone hill radar observations of storm enhanced density and low and high altitude satellite measurements of the perturbation of the outer plasmasphere during the march 31 2001 geomagnetic storm we find that storm enhanced density sed and plumes of greatly elevated tec are associated with the erosion of the outer plasmasphere by strong sub auroral polarization electric fields the sed tec plumes identified at low altitude map closely onto the magnetospheric determination of the boundaries of the plasmapause and plasmaspheric tail determined by euv imaging from the image spacecraft characteristics of the sed tec plumes tails for the march 31 2001 event are tec 100 tecu f region sunward velocity 1000 m s sunward flux 5 1024 ions s 1 total transport to dayside magnetopause merging region 3 hr event 5 1028 ions

polar motion of a viscoelastic earth due to glacial cycle mass loading the growth and decay of ice sheets can change the symmetry axis of the global mass distribution and thus excite motion of the rotation axis of the earth we develop a simple normal mode expansion of the operator which converts surface load histories into polar motion histories and use it to characterize the polar motion response to arbitrary surface loading excitation in terms of gain and phase for a wide range of earth models and excitation time scales uncertainties in loading history presently limit the utility of constraints on mantle rheology which can be obtained from matching the present direction and rate of motion of the pole because of its magnitude and distance from the pole the laurentide ice sheet alone can induce motion of the rotation pole by over 100 km this will influence the pattern of incident radiation on continents and oceans and may play a significant role in limiting ice sheet growth differential motion of the mantle and core on a glacial timescale may also influence the geomagnetic field

changes of the earth s rotation axis owing to advection of mantle density heterogeneities polar wander the secular motion of the earth s rotation axis relative to its surface has been studied for many years dynamical arguments1 3 show that polar wander can arise from the redistribution of mass in a plastic deformable earth the rate depending on both the rate of mass redistribution and the rate at which the earth s rotational bulge can readjust to the changing rotation axis here we use a viscosity structure obtained through geoid modelling4 a mantle flow field consistent with tomographic anomalies5 and time dependent lithospheric plate motions6 to calculate the advection of mantle density heterogeneities and corresponding changes in the degree two geoid during the cenozoic era we show that the rotation axis will follow closely any imposed changes of the axis of maximum non hydrostatic moment of inertia the resulting path of the rotation axis agrees well with palaeomagnetic results7 with the model predicting a current rate of polar motion that explains 40 of that observed geodetically8

redistributing earth s mass since the end of the last glaciation postglacial rebound of earth9s crust has resulted in a net transfer of mass from the equatorial regions to high latitudes this small mass transfer has been monitored for 25 years but a report by cox and chao suggests that since 1998 the mass transfer has changed direction in their perspective cazenave and nerem discuss possible mechanisms that may have caused this change

dynamic topography and lithospheric stresses since 400 ma we present a global model of dynamic topography and lithospheric stresses for the last 400 ma our starting point is a simple geodynamic model combining both contributions of subducted lithosphere and long wavelength upwellings in a reference frame linked to the fixed african plate a dominant feature of plate tectonics is the quasi permanence of a girdle of subductions around the pacific ocean or its ancestor which creates large wavelength positive topography anomaly within the ring they form the superimposition of the resultant extension with the one induced by the dome leads to a permanent extensional regime over africa and the future indian ocean which creates faults with azimuth directions depending on the direction of the most active part of the ring of subductions we thus obtain fractures with nw se azimuth during the period 275 165 ma parallel to the strike of the subduction zone of the west south american active margin which appears to be very active during this period between 155 95 ma subduction became more active along the eastern australian coast involving a change in the direction of the faults toward an e w direction in agreement with the observed fault systems between africa and india antartica and australia during the mesozoic and the cenozoic we correlate the permanent extensional regime over africa and indian ocean with the observed rift systems finally we emphasize the role of three primary hotspots as local additional contributors to the stress field imposed by our proposed subduction doming system which help in the opening of indian and south atlantic oceans

statistical analysis of the plasmaspheric plume at the magnetopause 1 during times of enhanced magnetospheric convection cold dense plasma from the plasmasphere can form a plume extending sunward toward the dayside magnetopause a statistical study is presented of cold high density plasmaspheric plasma at the magnetopause observations from the time history of events and macroscale interactions themis spacecraft show the plume to be present at the dayside magnetopause during 12 5 148 of 1184 of the crossings its most common location in magnetic local time when contacting the magnetopause is at 13 6 h the magnetopause crossings show evidence for reconnection in 68 of events with the plume while only 47 of events without plume although the plume is more likely to be observed at the magnetopause when reconnection is occurring the typical reconnection jet velocity is lower for plume events than nonplume events indicating the presence of the plume may be slowing the efficiency of the reconnection process