rectification of the madden julian oscillation into the enso cycle an ocean general circulation model forced with idealized purely oscillating wind stresses over the western equatorial pacific similar to those observed during the madden julian oscillation mjo developed rectified low frequency anomalies in sst and zonal currents compared to a run in which the forcing was climatological the rectification in sst resulted from increased evaporation under stronger than normal winds of either sign from correlated intraseasonal oscillations in both vertical temperature gradient and upwelling speed forced by the winds and from zonal advection due to nonlinearly generated equatorial currents the net rectified signature produced by the mjo like wind stresses was sst cooling about 0 48c in the west pacific and warming about 0 18c in the central pacific tending to flatten the background zonal sst gradient it is hypothesized that in a coupled system such a pattern of sst anomalies would spawn additional westerly wind anomalies as a result of sst induced changes in the low level zonal pressure gradient this was tested in an intermediate coupled

dependence of the energy balance of the greenland ice sheet on climate change influence of katabatic wind and tundra the summer time atmospheric circulation at the margin of a large ice sheet with an extended adjacent tundra is investigated with a two dimensional atmospheric model the assumed topography corresponds to the section through west greenland for which the greenland ice margin experiment gimex was performed with this model the local sensitivity of the ablation of the ice sheet to changes in the external parameters which pertain to climate is explored the main focus is the sensitivity which is related to atmospheric dynamics a comparison is made between the results with an exposed tundra and results with a snow covered tundra in the latter case the katabatic wind is strongly reduced close to the ice margin so that the downward sensible heat flux for the ablation zone is more than halved this shows that the influence of the exposed tundra on the energy balance of the ice sheet is important increasing the initial air temperatures leads to a stronger katabatic wind as a consequence the downward sensible heat flux at the ablation zone is strongly enhanced neglecting the change of the katabatic wind would lead to a much smaller growth of this flux which shows that the presence of an exposed tundra increases the sensitivity of the energy balance of the ice sheet to climate change for those runs the large scale wind is zero but in the presence of an inland directed large scale wind a strong surface wind parallel to the glacier front is found to develop above the ablation zone by which the sensible heat flux is increased the advection of heated air from the tundra to the ice sheet plays a lesser role

kinematic considerations for mantle mixing recent experimental and computational studies tal and computational mixing studies in highly controlled show that islands u mixedrcgions that donot interactwith flows show that even seemingly inconsequential errors in the surrounding regions are ubiquitous features in chaotically computed velocity field of 3 d or time dependent flows can advecting fluids such is ands uitenaturall account for the geochemically inferred coexistence of apparently distinct long lived geochemical heterogeneity with relatively homo geneous regions of an actively convecting mantle these results also indicate that mixing patterns the set of islands and folds characterizing the large scale material advection are sensitive to small variations in the rheology of the fluid therefore interpretation of numerical simulations of mantle transport and mixing is less straightforward than currently supposed computational studies of analytic flow solutions with systematically introduced and controlled errors indi cate that mantle simulations are unlikely to accurately com pute individual trajectories for even moderate time but that tmjectory ensembles can be accuntely computed for long time significantly computations also indicate that mixing and transport resultsmay not evolve smoothly with increased rheological realism

maintenance of northern summer stationary waves in a gcm abstract the maintenance of northern summer stationary waves is studied with data from a 15 year integration of the general circulation model gcm experiment performed at the geophysical fluid dynamics laboratory the model has relatively high resolution rhomboidal 30 wavenumbers 9 vertical levels and simulates the summertime stationary waves reasonably well a steady linear baroclinic model is used to understand the various forcing mechanisms for the northern summer stationary waves the linear model response to global diabatic heating is found to play a dominant role in maintaining the summertime stationary waves in the gcm especially in the subtropics this response to diabatic heating shows a baroclinic structure in the vertical with a node at about 0 5 on the other hand stationary nonlinear interaction terms are found to be largely responsible for the extratropical equivalent barotropic stationary wave features it is hypothesized that this nonlinear interaction is a result of the therm

ocean temperature and salinity components of the madden julian oscillation observed by argo floats new diagnostics of the madden julian oscillation mjo cycle in ocean temperature and for the first time salinity are presented the mjo composites are based on 4 years of gridded argo float data from 2003 to 2006 and extend from the surface to 1 400 m depth in the tropical indian and pacific oceans the mjo surface salinity anomalies are consistent with precipitation minus evaporation fluxes in the indian ocean and with anomalous zonal advection in the pacific the argo sea surface temperature and thermocline depth anomalies are consistent with previous studies using other data sets the near surface density changes due to salinity are comparable to and partially offset those due to temperature emphasising the importance of including salinity as well as temperature changes in mixed layer modelling of tropical intraseasonal processes the mjo forced equatorial kelvin wave that propagates along the thermocline in the pacific extends down into the deep ocean to at least 1 400 m coherent statistically significant mjo temperature and salinity anomalies are also present in the deep indian ocean

geostrophic circulation in the tropical north pacific ocean based on argo profiles absolute geostrophic currents in the north pacific ocean are calculated from the newly gridded argo profiling float data using the p vector method for the period of 2004 11 the zonal geostrophic currents based on the argo profile data are found to be stronger than those based on the traditional world ocean atlas 2009 woa09 data a westward mean geostrophic flow underneath the north equatorial countercurrent is identified using the argo data which is evidenced by sporadic direct current measurements and geostrophic calculations in history this current originates east of the date line and transports more than 4 x 10 6 m 3 s 1 of water westward in the subsurface northwestern tropical pacific ocean the authors name this current the north equatorial subsurface current the transport in the geostrophic currents is compared with the sverdrup theory and found to differ significantly in several locations analyses have shown that errors of wind stress estimation cannot account for all of the differences the largest differences are found in the area immediately north and south of the bifurcation latitude of the north equatorial current west of the date line and in the recirculation area of the kuroshio and its extension where nonlinear activities are vigorous it is therefore suggested that the linear dynamics of the sverdrup theory is deficient in explaining the geostrophic transport of the tropical northwestern pacific ocean

a characteristics based method for solving the transport equation and its application to the process of mantle differentiation and continental root growth summary purely advective transport of composition is of major importance in the geosciences and efficient and accurate solution methods are needed a characteristics based method is used to solve the transport equation we employ a new hybrid interpolation scheme which allows for the tuning of stability and accuracy through a threshold parameter eth stability is established by bilinear interpolations and bicubic splines are used to maintain accuracy with this scheme numerical instabilities can be suppressed by allowing numerical diffusion to work in time and locally in space the scheme can be applied efficiently for preliminary modelling purposes this can be followed by detailed high resolution experiments first the principal effects of this hybrid interpolation method are illustrated and some tests are presented for numerical solutions of the transport equation second we illustrate that this approach works successfully for a previously developed continental evolution model for the convecting upper mantle in this model the transport equation contains a source term which describes the melt production in pressure released partial melting in this model a characteristic phenomenon of small scale melting diapirs is observed de smet et al 1998 de smet et al 1999 high resolution experiments with grid cells down to 700 m horizontally and 515 m vertically result in highly detailed observations of the diapiric melting phenomenon

a mechanistic model of the northern annular mode 1 the northern annular mode nam is the leading mode of variability in the northern hemisphere the nam consists of a meridional dipole of the zonal mean zonal wind that extends into the stratosphere during the winter season during the high index state of the nam high latitude westerly winds are stronger than normal leading to a stronger and colder polar vortex over the past few decades observations show a trend toward higher nam index values to investigate whether this trend is a result of natural variability or is related to greenhouse warming a mechanistic model is developed that provides a simple analogue of the nam the model represents the interaction between the zonally symmetric flow and planetary waves for two meridional modes of variation greenhouse warming is specified in the model by varying the radiative equilibrium meridional temperature gradient variations in the second meridional mode qualitatively resemble those of the observed nam model runs that correspond to larger greenhouse gas concentrations yield on average higher nam index values

on the nonlinear versus linearized lower boundary conditions for topographically forced stationary long waves abstract for quasi geostrophic stationary long waves forced by topography the nonlinear lower boundary condition is derived in terms of the geopotential height and compared with the linearized version the common practice of replacing terms describing the flow over and around a mountain by upstream zonal flow over the mountain and evaluating the resulting condition at sea level is found to be a good approximation for the cases considered and does not need to be modified as sometimes suggested specifically it is found that this approximation does not affect for most cases the lower boundary condition expressed in terms of the geopotential height provided that the stationary wave is not near resonance at resonance the eddy advection terms may become important for large amplitude waves when dissipation and surface diabatic heating are taken into account

second and first baroclinic kelvin modes in the equatorial pacific at intraseasonal timescales 1 topex poseidon sea level and time series from the tao tropical atmosphere ocean array of moorings over 1992 1999 are used to investigate the spatiotemporal characteristics of equatorial kelvin waves in the pacific at period shorter than 180 days spectral analyses show high oceanic energy in two separate bands of period around 70 days and 120 days signals are coherent in both bands all along the equator ocean general circulation model ogcm simulations forced by different wind stress fields are also analyzed and exhibit the same features observed and modeled sea level dynamic height and 20 c isotherm depth band pass filtered around 70 days show an eastward propagation at phase speed of 2 4 2 9 m s 1 typical of the first baroclinic kelvin mode the meridional and vertical structures of the equatorial waves at the onset of the 1997 el nino are also those expected for a first kelvin mode at 120 day period phase speeds meridional and vertical structures are closer to those expected for a second baroclinic mode both modes are nevertheless present in the two frequency bands a simple kelvin wave model shows that the wind at 120 day period seems to force the kelvin waves at the same period however the predominance of second baroclinic mode at 120 day period cannot be explained solely by the characteristics of the wind ogcm simulations rather suggest the importance of internal oceanic processes such as vertical redistribution of energy from first to second baroclinic mode as the waves propagate eastward model outputs over 1984 1999 indicate that these equatorial kelvin waves at 70 and 120 day period may have an effect on el nino since they seem to be stronger at its onset

estimated global hydrographic variability an estimate is made of the three dimensional global oceanic temperature and salinity variability omitting the seasonal cycle both as a major descriptive element of the ocean circulation and for use in the error estimates of state estimation historical hydrography recent data from the world ocean circulation experiment and argo profile data are all used root mean square vertical displacements in the upper 300 m of the ocean are generally smaller than 50 m except in energetic boundary currents and in the north atlantic subpolar gyre variability in temperature and salinity is strongly correlated below the top 100 m salinity contributions to sea surface height variability appear more significant at low latitudes than expected possibly resulting from advective and diffusive processes results are generally consistent with altimetric variability under two simple kinematic hypotheses and much of the observed structure coincides with known dynamical features a large fraction of the sea surface height variability is consistent with the hypothesis of dominance of the first baroclinic mode

time scales of upper ocean temperature variability inferred from the pirata data 1997 2000 1 time series from the pirata 10 minute measurements are investigated in order to study the upper ocean thermal field time scales of variability using the serial covariance power spectra method and wavelet analysis this is one of the few studies that analyze in time and space the pirata buoy data in the region analysis of the depth of the 20 c isotherm show distinct patterns for the northwestern atlantic at 8n 38w and the southeastern atlantic at 10s 10w in the west warm surface waters are accompanied by a shallower thermocline while in the east warm surface waters are associated with its deepening consistent with houghton 1991 at higher frequencies the dominant signals in sea surface temperature are the diurnal and semi diurnal cycles spectral analysis of the depth of the 20 c isotherm show a predominance of the semi diurnal period in the eastern atlantic there are two additional dominant bands in the spectra 10 14 days 25 27 days and for the depth of the 20 c isotherm there is also a lower frequency band at 20 40 days associated with tropical instability waves at the equator the first band can be associated with atmospherically forced motions and the lower frequency band with barotropic instability waves

understanding the seasonality of orographically forced stationary waves interaction between mechanical and thermal forcing abstract idealized simulations of the atmosphere s stationary response to the rockies tibetan plateau and the greenland ice sheet are made using a nonlinear quasigeostrophic model and are compared to observations observational data indicate low level heating cooling occurs above the rockies and tibet in the summer winter low level cooling is found above greenland in both seasons the atmosphere responds to both diabatic heating termed thermal forcing and low level flow being obstructed by the mountain s presence termed mechanical forcing the response to thermal and mechanical forcing together can be very different from the response to either forcing individually the presence of modest low level heating or cooling 1 5 k day 1 causes significant changes to the mechanical forcing and thereby to the stationary wave response for example while the nonlinear response to mechanical forcing and low level heating is characterized by a cyclone over the orography the response to mechanical forc

dynamical consequences on fast subducting slabs from a self regulating mechanism due to viscous heating in variable viscosity convection the authors have studied 2 d time dependent convection for a rheology which is both non newtonian and temperature dependent strong effects associated with viscous heating are found in the downwelling sheets which are heated on both sides with an intensity around o 10 sup 2 times the chondritic value the magnitude of viscous heating increases strongly with the subduction speed the slab interior is weakened by viscous heating and slab breakoff then takes place this process provides a self regulating mechanism for governing the speed of intact slabs able to reach the deep mantle timescales associated with viscous heating are quite short a few million years internal heating by radioactivity decreases the amount of shear heating 13 refs 5 figs

orographically induced stationary waves dependence on latitude abstract a general circulation model gcm with idealized boundary conditions is used to study the effects of a mountain s latitudinal position on the stationary wave response in each of a series of experiments the only asymmetry in the boundary conditions is a gaussian shaped mountain with an e folding width of 15 latitude placed at 0 15 30 45 and 60 latitude in separate integrations the stationary wave response in the gcm is analyzed using a linearized primitive equation model a 3d wave flux vector and a barotropic ray tracing technique stationary waves in the gcm are generated by modifications to the diabatic heating field termed thermal forcing and by obstructing the surface winds termed mechanical forcing with a mountain at 0 latitude latent heating anomalies provide the forcing mechanism in the 15 mountain experiment forcing by anomalous latent heating is also found but mechanical forcing which occurs within the easterlies seems to dominate in the 30 45 and 60 mounta

on the relation between seismic anisotropy and finite strain because seismic anisotropy in the upper mantle is due primarily to lattice preferred orientation lpo of olivine crystals induced by deformation observations of anisotropy can provide constraints on mantle deformation and flow in this paper we use a previously published theory for deformation induced lpo ribe and yu 1991 to quantify the relation between seismic anisotropy and deformation for two model compositions a pure olivine dunite aggregate and a harzburgite comprising 70 olivine and 30 enstatite analytical and numerical solutions of the governing equations show that the predicted lpo and hence also the seismic anisotropy depends only on the finite strain and not on the deformation path by which that strain is produced the magnitude of the anisotropy depends only on the ratios c1 c2 and c2 c3 where c1 c2 c3 are the lengths of the principle axes of the finite strain ellipsoid and the directions of maximum and minimum compressional wave velocity vp coincide with the axes c1 and c3 respectively we calculate the percent anisotropies for compresional and shear waves propagating along the three principle axes of the finite strain ellipsoid as functions of the axial ratios c1 c2 and c2 c3 for our two model compositions however inferences of the magnitude of finite strain obtained using these results are likely to be minimum estimates because our theory neglects the effects of dynamic recrystallization finally we present as a byproduct of this study a new direct method for calculating the finite strain produced by an arbitiary deformation history

northern winter stationary waves theory and modeling a review is provided of stationary wave theory the theory for the deviations from zonal symmetry of the climate to help focus the discussion the authors concentrate exclusively on northern winter several theoretical issues including the external rossby wave dispersion relation and vertical structure critical latitude absorption the nonlinear response to orography and the interaction of forced wave trains with preexisting zonal asymmetries are chosen for discussion while simultaneously presenting a decomposition of the wintertime stationary wave field using a nonlinear steady state model

on the three dimensional propagation of stationary waves abstract a locally applicable nonzonally averaged conservation relation is derived for quasi geostrophic stationary waves on a zonal flow a generalization of the eliassen palm relation the flux which appears in this relation constitutes it is argued a useful diagnostic of the three dimensional propagation of stationary wave activity this is illustrated by application to a simple theoretical model of a forced rossby wave train and to a northern hemisphere winter climatology results of the latter procedure suggest that the major forcing of the stationary wave field derives from the orographic effects of the tibetan plateau and from nonorographic effects diabatic heating and or interaction with transient eddies in the western north atlantic and north pacific oceans and siberia no evidence is found in the data for wave trains of tropical origin forcing by the orographic effects of the rocky mountains seems to be of secondary importance

comparison of mixing properties in convection with the particle line method spatial resolution in mixing processes is an acute problem we propose a line method akin to the contour dynamics technique which is an extension of the particle method but with the particles redistributed on the line with time we have used up to 10 5 particles per line and ten lines to investigate the dynamical and structural properties of mixing for both newtonian and non newtonian temper ature dependent viscosity convection in 2d geometry the spatial structures and the time history of the lines formed in newtonian convection are dierent from those produced in non newtonian convection which has the tendency for producing long living horizontal structures ecient mixing in the upper mantle would be inhibited by non newtonian rheology

scales of variability in the equatorial pacific inferred form tropical atmosphere ocean buoy array abstract the highly temporally resolved time series from the tropical atmosphere ocean moored buoy array are used to evaluate the scales of thermal variability in the upper equatorial pacific the tao array consists of nearly 70 deep ocean moorings arranged nominally 15 longitude and 2 3 latitude apart across the equatorial pacific the bulk of the data from the array consists of daily averages telemetered in real time with some records up to 15 years long however at several sites more finely resolved data exist in some cases with resolution of 1 minute these data form the basis for spectral decomposition spanning virtually all scales of variability from the brunt vaiala frequency to the el nino southern oscillation timescale the spectra are used to define the signal to noise ratio as a function of sample rate and frequency and to investigate the effects of aliasing that results from sparser sampling such as ship based observational techniques the results show that the signal to noise ratio is

enso and short term variability of the south equatorial current entering the coral sea abstracthistorical section data extending to 1985 are used to estimate the interannual variability of transport entering the coral sea between new caledonia and the solomon islands typical magnitudes of this variability are 5 8 sv sv 106 m3 s 1 in the 0 400 m layer relative to 400 m and 8 12 sv in the 0 2000 m layer relative to 2000 m on a mean of close to 30 sv relative to 2000 m transport increases a few months after an el nino event and decreases following a la nina interannual transport variability is well simulated by a reduced gravity long rossby wave model vigorous westward propagating mesoscale eddies can yield substantial aliasing on individual ship or glider surveys since transport variability is surface intensified and well correlated with satellite derived surface geostrophic currents a simple index of south equatorial current transport based on satellite altimetry is developed

the evolution of material surfaces in convection with variable viscosity as monitored by a characteristics based method we have studied the evolution of material surfaces in strongly time dependent convection for both newtonian and non newtonian temperature and depth dependent rheologies a spline characteristic method has been employed the method of characteristics is second order in time and fourth order in space our strategy is to employ a very dense grid for the material surface field with about 50 to 100 times more points than for the temperature field grid we have detected sharp entrainment of the surrounding material into both the ascending and descending flow structures we have observed the breakoff process involving the descending plume mixing takes place very differently for the two rheologies with time small vortical features are developed inside the newtonian plumes while unmixed islands still persist in the non newtonian flow

orographically forced planetary waves in the northern hemisphere winter steady state model with wave coupled lower boundary formulation abstract a planetary wave model has been developed in which the orographic forcing at the lower boundary arising from the kinematically induced vertical motion is due to the total flow impinging on the mountains rather than just the zonal mean basic state component of the flow over the mountains used in previous models consequently the effects of the vertical motions produced by the eddies at the lower boundary are included and are found to be as large if not larger than the zonal mean component the model remains linear mathematically but all the planetary waves become coupled through the lower boundary condition lbc and the model wave equations have to be solved for simultaneously a contrast is drawn between the wave coupled solutions and the solutions using the traditional lower boundary formulation in which the planetary waves are decoupled the model is symmetric about the equator and uses the linear balance set of equations on the sphere with full spherical geometry and spherical harmonic f

dynamical consequences of depth dependent thermal expansivity and viscosity on mantle circulations and thermal structure the effects of both depth dependent thermal expansivity and depth dependent viscosity on mantle convection have been examined with two dimensional finite element simulations in aspect ratio ten boxes surface rayleigh numbers between 107 and 6 107 have been considered the effects of depth dependent properties acting singly or in concert are to produce large scale circulations with a few major upwellings the interior of the mantle is cooled by the many cold instabilities which are slowed down and eventually swept about by the large scale circulation the interior temperature of the mantle can be influenced by the trade off between depth dependent properties and internal heating for chondritic abundance of internal heating and depth dependent thermal expansivity the viscosity increase across the mantle can be no greater than a factor of around ten in order to keep the lower mantle adiabatic the thermal contrasts between the cold blobs and the surrounding mantle are strongly reduced by depth dependent properties whereas the lateral differences between the hot upwelling and the ambient lower mantle can be significant over several hundred degrees depth dependent properties also encourage the formation of a stronger mean flow in the upper mantle which may be important for promoting long term polar motions

monthly period oscillations in the pacific north equatorial countercurrent monthly period oscillations in temperature and velocity in the vicinity of the north equatorial countercurrent along 140 w are examined using moored time series data collected during 1988 1989 these oscillations which presumably derive their energy from instability of the large scale shear of the zonal equatorial current system are found to be energetic across a broad band of periods of about 15 50 days along 7 n wavelike motions at these periods propagate westward with a phase speed of about 30 40 cm s 1 and a zonal wavelength of 750 1150 km the oscillations are approximately in geostrophic balance with the thermal field with the velocity vector rotating anticyclonically around westward propagating high sea level centers zonal volume transport variations associated with these waves between 5 and 9 n at 20 180 m depth have a standard deviation of about 4 1 sv with peak to peak changes in some instances approaching 20 sv maximum temperature variance along 140 w occurs between 5 and 7 n at 100 150 m depth in a region of strong mean vertical and meridional temperature gradient associated with a thermocline sloping upward to the north at the surface maximum temperature variability occurs from 2 to 5 n in the vicinity of the strong sea surface temperature front north of the equator analysis of the upper ocean temperature balance at 7 n 140 w reveals that meridional advection is important both in the surface layer and in the thermocline vertical advection estimated using vertical velocity calculated from a simplified linear vorticity balance is also important in the thermocline where it contributes a variance comparable to that of meridional advection zonal advection is likely to be significant in the upper 80 m below which it is probably of secondary importance compared to meridional and vertical advection one consequence of advection in the temperature balance is that variance is shifted toward lower frequencies in temperature vis a vis velocity spectra this red shift may account for the apparent difference between periods for instability waves inferred from near equatorial meridional velocity spectra and slightly longer periods reported for oscillations of the sea surface temperature front north of the equator based on satellite imagery

interannual variability of deep convection over the tropical warm pool satellite data show that the total amount of deep convection was nearly constant from year to year over the warm pool region of the tropical indian and pacific oceans but the spatial distribution varied in the 1986 1987 warm el nino southern oscillation event the maximum of deep convective activity was over the high sea surface temperature sst of the west central pacific with a local minimum over the eastern indian ocean in the 1988 1989 cold enso event the maximum convective activity switched to the eastern indian ocean with a minimum over the west central pacific the sst changed very little over the eastern indian ocean from year to year and the centers of convective activity were always collocated with the four month mean low level westerlies in each year the latitude of the cloudy region of the intraseasonal oscillation iso varied interannually the interannual differences in deep convective activity over the warm pool were accounted for almost exclusively by the occurrence or nonoccurrence of extremely large long lasting deep mesoscale cloud systems cloud tops 208 k with horizontal dimensions 300 700 km such cloud systems occurred more frequently than normal over the western pacific during the warm enso event and over the eastern indian ocean during the cold event they occurred more frequently over the tropical eastern indian and western pacific oceans than over the maritime continent thus accounting for the seesaw pattern of the observed cold cloudiness between the two oceanic regions on both interannual and intraseasonal timescales