utilizing the aspect sea ice thickness data set to evaluate a global coupled sea ice ocean model 1 simulated sea ice thickness in the orca2 lim coupled sea ice ocean model is compared with thicknesses from the antarctic sea ice processes and climate aspect database we find a qualitative agreement of the large scale patterns of ice thickness distribution regional averages for the various sectors of the southern ocean yield a very good correspondence between observations and model data exceptions are the eastern bellingshausen and northwestern weddell seas a poor representation of the antarctic peninsula in the atmospheric forcing data and the related overestimation of westerly winds in this region lead to a spurious accumulation of sea ice on the western side of the peninsula and to an underestimation of sea ice coverage on the eastern side since the spatial scale of observations is not comparable to the size of a model grid cell there is little agreement between individual observations and the corresponding model ice thicknesses a model analysis of the seasonal and interannual variability indicates that the aspect data underestimate the climatological ice thickness in the central and southern weddell sea and the eastern ross sea by up to 1 m because of a winter bias in the observations an overestimation of similar magnitude is expected in the bellingshausen sea ice thickness data in most of the indo pacific sector appear to be representative for the long term climatology a model estimate of the bias is used to compute a revised distribution of climatological sea ice thickness

western pacific interannual variability associated with the el nino southern oscillation observations of sea surface temperature sst sea level pressure slp surface wind and outgoing longwave radiation olr show that the el nino southern oscillation enso displays western pacific anomaly patterns in addition to eastern pacific anomaly patterns during the warm phase of enso warm sst and low slp anomalies in the equatorial eastern pacific and low olr anomalies in the equatorial central pacific are accompanied by cold sst and high slp anomalies in the off equatorial western pacific and high olr anomalies in the off equatorial far western pacific also while the zonal wind anomalies over the equatorial central pacific are westerly those over the equatorial far western pacific are easterly the nearly out of phase behavior between the eastern and western tropical pacific is also observed during the cold phase of enso but with anomalies of opposite sign these western pacific interannual anomaly patterns are robust features of enso independent of data sets it is argued that equatorial easterly westerly wind anomalies over the far western pacific during the warm cold phase of enso are initiated by off equatorial western pacific cold warm sst anomalies and that these winds are important for the evolution of enso an atmosphere model is employed to demonstrate that small off equatorial western pacific cold warm sst anomalies compared to those in the east are sufficient to produce equatorial easterly westerly wind anomalies as observed over the far western pacific the coupled ocean atmosphere model of zebiak and cane is then modified to investigate the evolution of the western pacific interannual anomaly patterns in a coupled ocean atmosphere system by including a meridional structure to the subsurface temperature parameterization in the western pacific the modified model produces both western and eastern pacific interannual anomaly patterns

planetary scale selection of the madden julian oscillation in an air sea coupled dynamic moisture model the authors present an air sea coupled dynamic moisture asdm model to explore the mechanism of preferred planetary scale of the madden julian oscillation mjo this asdm model extended from the original frictionally coupled dynamic moisture model and a mixed layer model can present a good simulation of planetary scale characteristics of the mjo including a slow eastward propagation of 5 m s 1 coupled rossby kelvin wave like structure and phase leading of convective center by warm sea surface temperature sst it is interesting that the planetary scale selection in terms of instability is only found in the nonlinear asdm model with the assumption of positive only heating such a scale selection however cannot be found in the asdm model with linear heating or in an uncoupled atmosphere model the essential mechanism for the scale selection is nonlinear positive only heating and the air sea interaction primarily provides an instability source to support this scale selection this scale selection is attributed to different phase speeds of coupled moist rossby kelvin waves and dry kelvin waves from short wave initial perturbations the easterly wind anomalies of eastward propagating dry kelvin waves from a stronger wave component will catch up with other weaker moist components and suppress their westerly wind anomalies resulting in weak sst gradient as well as reduced moisture convergence and precipitation for these suppressed components as a result the wavenumber one structure is selected the warm pool like mean state will select the stronger component among the initial short wave perturbations and accelerate this scale selection process these results provide new insight into mjo mechanism in terms of air sea interaction

turbulent heat flux in the upper ocean under sea ice turbulence data from three arctic drift station experiments demonstrate features of turbulent heat transfer in the oceanic boundary layer time series analysis of several w t records shows that heat and momentum flux occur at nearly the same scales typically by turbulent eddies of the order of 10 20 m in horizontal extent and a few meters in vertical extent probability distribution functions of w t have large skewness and kurtosis where the latter confirms that most of the flux occurs in intermittent events with positive and negative excursions an order of magnitude larger than the mean value an estimate of the eddy heat diffusivity in the outer ekman part of the boundary layer based on measured heat flux and temperature gradient during a diurnal tidal cycle over the yermak plateau slope north of fram strait agrees reasonably well with the eddy viscosity with values as high as 0 15 m2 s 1 an analysis of measurements made near the ice ocean interface at the three stations shows that heat flux increases with both temperature elevation above freezing and with friction velocity at the interface it also reveals a surprising uniformity in parameters describing the heat and mass transfer e g the thickness of the transition sublayer from a modified version of the yaglom kader theory is about 10 cm at all three sites despite nearly a fivefold difference in the under ice roughness z0 which ranges from approximately 2 to 9 cm a much simplified model for heat and mass transfer at the ice ocean interface suggested by the relative uniformity of the heat transfer coefficients at the three sites is outlined

relative roles of elevated heating and surface temperature gradients in driving anomalous surface winds over tropical oceans abstract elevated heating by cumulus convection and sea surface temperature gradients are both thought to contribute to surface winds over tropical oceans the relative strength and role of each mechanism is examined by imposing forcing derived from data on a linear primitive equation model with idealized parameterizations for the two forcings and comparing the response with observed surface winds two test cases are studied one related to the el nino southern oscillation and the other related to the dipole mode in the tropical atlantic it is found that in both cases elevated heating dominates the surface zonal wind response and contributes significantly to the meridional wind response especially in the subtropics and the south pacific and south atlantic convergence zone regions surface temperature gradients dominate the meridional wind forcing in regions near the equator with strong meridional temperature gradients

modis based mosaic of antarctica moa data sets continent wide surface morphology and snow grain size abstract we present digital image mosaics of surface morphology and optical snow grain size for the antarctic continent and surrounding islands assembled from 260 moderate resolution imaging spectroradiometer modis images the products are derived from modis band 1 red light 647 nm and band 2 infrared 857 nm orbit swath data acquired during the 2003 2004 austral summer multiple images of all areas are combined in a data cumulation scheme to improve spatial resolution and increase radiometric content of the mosaics the component images were de striped geo registered and re sampled to the projection grid using the modis swath to grid toolbox ms2gt software a 125 m ground equivalent polar stereographic projection was used identical to previous radar image mosaics and similar to several other continent wide data sets geo location accuracy of the final mosaics is better than 125 m swath acquisition times were limited to the range 05 00 13 30 ut to provide broad but uniform mosaic illumination regions of cloud cover blowing snow and intense forward scattering were masked prior to compositing the moa snow grain size data set image provides the first continent wide semi quantitative map of mean summer snow firn and blue ice grain size optical grain size radius was determined using a normalized difference index derived from modis band 1 and band 2 rad values atmospheric correction adjustments for directional reflectance variation and snow grain size estimation were accomplished by a look up table generated by a combination of published models of snow spectral reflectance and atmosphere radiative transfer validation of the snow grain size image is provided by in situ spectra of snow covered sea ice made in october 2003 we use the new data sets to determine major ice shelf areas and shelf edge coastline and ice grounding line vector files and determine areas of selected blue ice regions these data sets are available for download at http nsidc org data moa

atmospheric convergence feedback in a simple model for el nino abstract a parameterization is developed for the feedback between dynamics and heating associated with moisture convergence in the tropical atmospheric boundary layer the feedback improves the ability of a simple model to simulate observed anomalies of the tropical atmosphere during el nino events in particular two features of the observations are reproduced by including the feedback process the smaller scale of atmospheric anomalies as compared to sst anomalies and the focusing of the anomalies in the vicinity of the mean convergence zones the principal remaining shortcomings of the model are discussed

studies of the antarctic sea ice edge and ice extent from satellite and ship observations abstract passive microwave derived ice edge locations in the antarctic are assessed against in situ observations from ships between 1989 and 2000 during the growth season march october the ship data agrees with satellite data very well with r2 values of 0 99 and 0 97 for the bootstrap and team algorithms respectively during the melt season november february the agreement is not so good with the passive microwave ice edge typically 1 2 of latitude south of the observations this is due to the low concentration and saturated nature of the ice and the r2 values for this period are 0 92 and 0 80 for the bootstrap and team algorithms respectively sensitivity studies show that such an offset in the summer ice edge location can cause significant errors in trend studies of the extent of sea ice cover in the southern ocean the passive microwave ice concentration at the ice edge observed by ship varies greatly averaging 14 for the team algorithm and 19 for the bootstrap comparisons between passive microwave data and sar landsat and ols data during the ice growth season show that while small scale details in ice edge location are lost the passive microwave data generally provide good and consistent representation of the higher resolution imagery

maintenance of the sea ice edge abstract a coupled global climate model is used to evaluate processes that determine the equilibrium location of the sea ice edge and its climatological annual cycle the extent to which the wintertime ice edge departs from a symmetric ring around either pole depends primarily on coastlines ice motion and the melt rate at the ice ocean interface at any location the principal drivers of the oceanic heat flux that melts sea ice are absorbed solar radiation and the convergence of heat transported by ocean currents the distance between the ice edge and the pole and the magnitude of the ocean heat flux convergence at the ice edge are inversely related the chief exception to this rule is in the east greenland current where the ocean heat flux convergence just east of the ice edge is relatively high but ice survives due to its swift southward motion and the protection of the cold southward flowing surface water in regions where the ice edge extends relatively far equatorward absorbed solar radiation is t

on the relationship between sst gradients boundary layer winds and convergence over the tropical oceans a linear mixed layer model that skillfully reproduces observed surface winds and convergence over the tropicaloceans is used to examine the relative influenceof boundarylayer and free tropospheric processes on the distribution of climatological surface winds and convergence the semiempirical model assumes a subcloud layer momentum force balance between pressure gradients coriolis acceleration linearized friction and downward momentum mixing and it utilizes boundary conditions from the 40 yr ecmwf re analysis era 40 observed pressure gradients are linearly decomposed into boundary layer defined as the region below 850 hpa and free tropospheric components and the surface winds and convergence associated with these components are computed results show that surface zonal winds are predominantly associated with a combination of free tropospheric pressure gradients and downward momentum mixing whereas the distribution of convergence is primarily due to boundary layer temperature gradients which are closely related to sst gradients the authors conclude that the climatological distribution of boundary layer convergence is primarily a function of the pattern of sst gradients and is better regarded as a cause rather than a consequence of deep convection

investigating the variability of the arctic sea ice thickness in response to a stochastic thermodynamic atmospheric forcing the natural low frequency variability of the sea ice thickness in the arctic is investigated based on a 10 000 years simulation with a one dimensional thermodynamic sea ice model forced by random perturbations of the air surface temperature and solar radiation the simulation results suggest that atmospheric random perturbations are integrated by the sea ice moreover those perturbations occurring at the onset of ice melting force the largest ice thickness anomalies which are successively amplified in summer by the albedo feedback and damped in winter by the feedback of the heat conduction through the ice they also result in a global shift of the melting season which in the mean annual cycle leads to earlier melting as compared to the mean climatological cycle the power spectrum of the ice anomalies suggests that the thickness of the perennial ice should vary preferentially on a time scale of approximately 20 years the shape of the spectrum is consistent with that of a first order markov process in which the characteristic time scale of the ice fluctuations would be the relaxation time scale associated with the linear feedback the equivalent markov model is constructed by linearizing the ice growth rate anomaly equations and allows us to derive an analytical expression of the feedback and of the forcing of the anomalies the characteristic time scale depends explicitly on those model parameters involved in the atmosphere ice interaction but also on the mean seasonal characteristics of the forcing and of the ice thickness

remapping the thickness distribution in sea ice models in sea ice models with multiple thickness categories the ice thickness distribution evolves in time the evolution of the thickness distribution as ice grows and melts is analogous to one dimensional fluid transport and can be treated by similar numerical methods one such method remapping is applied here thickness categories are represented as lagrangian grid cells whose boundaries are projected forward in time the thickness distribution is approximated as a linear or quadratic polynomial in each displaced category and ice area and volume are transferred between categories so as to restore the original boundaries in simple test problems and in a single column model with forcing typical of the central arctic remapping performs significantly better than methods previously used in sea ice models it is less diffusive than a scheme that fixes the ice thickness in each category and behaves better numerically than a scheme that represents the thickness distribution as a set of delta functions also remapping converges faster i e with fewer thickness categories than the alternative schemes with five to seven categories the errors due to finite resolution of the thickness distribution are much smaller than the errors due to other sources linear remapping performs as well as the more complex quadratic version and is recommended for climate modeling its computational cost is minimal compared to other sea ice model components

influence of the sea ice thickness distribution on polar climate in ccsm3 abstract the sea ice simulation of the community climate system model version 3 ccsm3 t42 gx1 and t85 gx1 control simulations is presented and the influence of the parameterized sea ice thickness distribution itd on polar climate conditions is examined this includes an analysis of the change in mean climate conditions and simulated sea ice feedbacks when an itd is included it is found that including a representation of the subgrid scale itd results in larger ice growth rates and thicker sea ice these larger growth rates represent a higher heat loss from the ocean ice column to the atmosphere resulting in warmer surface conditions ocean circulation most notably in the southern hemisphere is also modified by the itd because of the influence of enhanced high latitude ice formation on the ocean buoyancy flux and resulting deep water formation changes in atmospheric circulation also result again most notably in the southern hemisphere there are indications that the itd also modifies simulated sea

a new paradigm for the predominance of standing central pacific warming after the late 1990s canonical el nino has a warming center in the eastern pacific ep but in recent decades el nino warming center tends to occur more frequently in the central pacific cp the definitions and names of this new type of el nino however have been notoriously diverse which makes it difficult to understand why the warming center shifts here we show that the new type of el nino events is characterized by 1 the maximum warming standing and persisting in the cp and 2 the warming extending to the ep only briefly during its peak phase for this reason we refer to it as standing cp warming cpw global warming has been blamed for the westward shift of maximum warming as well as more frequent occurrence of cpw however we find that since the late 1990s the standing cpw becomes a dominant mode in the pacific meanwhile the epochal mean trade winds have strengthened and the equatorial thermocline slope has increased contrary to the global warming induced weakening trades and flattening thermocline we propose that the recent predominance of standing cpw arises from a dramatic decadal change characterized by a grand la nina like background pattern and strong divergence in the cp atmospheric boundary layer after the late 1990s the anomalous mean cp wind divergence tends to weaken the anomalous convection and shift it westward from the underlying sst warming due to the suppressed low level convergence feedback this leads to a westward shift of anomalous westerly response and thus a zonally in phase sst tendency preventing eastward propagation of the sst anomaly we anticipate more cpw events will occur in the coming decade provided the grand la nina like background state persists

interhemispheric influence of the atlantic warm pool on the southeastern pacific abstract the atlantic warm pool awp is a large body of warm water comprising the gulf of mexico caribbean sea and western tropical north atlantic the awp can vary on seasonal interannual and multidecadal time scales the maximum awp size is in the boreal late summer and early fall with the largest extent in the year being about 3 times the smallest one the awp alternates with the amazon basin in south america as the seasonal heating source for circulations of the hadley and walker type in the western hemisphere during the boreal summer fall a strong hadley type circulation is established with ascending motion over the awp and subsidence over the southeastern tropical pacific this is accompanied by equatorward flow in the lower troposphere over the southeastern tropical pacific as dynamically required by the sverdrup vorticity balance it is shown by analyses of observational data and ncar community atmospheric model simulations that an anomalously large small awp during the boreal summer f

diagnostic studies of pacific surface winds abstract analyses are performed using surface winds derived from the monthly mean fsu pacific pseudo stress fields vorticity budget calculations reveal the relative contributions of various terms and allow simplification of the full momentum equations based on the simplified equations a procedure is developed for estimating surface pressure and then adjusting the winds the wind field adjustments fall well within the uncertainty of the data while allowing generally large imbalances in the vorticity budget to be removed completely further validation of the procedure is provided by comparisons between estimated and observed pressure anomalies the adjusted winds and pressure are then used to infer boundary layer and upper level forcing within the context of particular model formulations these forcing fields an compared with sea surface temperature outgoing longwave radiation and highly reflective cloud data in order to infer the dominant mechanisms contributing to observed surface circulation anom

discussion of a re assessment of phase equilibria involving two liquids in the system k2o al2o3 feo sio2 by g m biggar

exploring the initial errors that cause a significant spring predictability barrier for el nino events 1 within the zebiak cane model we identify two types of initial errors that have significant season dependent evolutions related to the spring predictability barrier spb for el nino events one type includes the sea surface temperature anomaly ssta errors that have a zonal dipolar pattern with positive anomalies in the central equatorial pacific and negative ones in the eastern equatorial pacific the other type consists of the ssta errors with a spatial structure opposite to that of the former type the zonal dipolar pattern shows negative anomalies in the central equatorial pacific and positive anomalies in the eastern equatorial pacific the patterns of these two types of errors are nearly opposite of each other the former causes the el nino event to be underpredicted and the latter causes the el nino event to be overpredicted for strong el nino events the former tends to have a larger effect on the predictions than the latter but for weak el nino events it is very difficult to determine which type of initial errors results in worse predictions it is thought that strong weak el nino events could be affected by strong weak nonlinearities there are also other initial errors however they do not yield considerable season dependent evolutions nor can a common characteristic be extracted from their patterns the two types of initial errors suggest two dynamical behaviors of error growth related to the spb in one case the initial errors grow in a manner similar to the el nino events in the other case the initial errors develop with a tendency opposite to the el nino events the two types of initial errors may capture the errors that exhibit significant season dependent evolutions related to the spb in addition they may provide information regarding the sensitive area of enso predictions because of their localized regions therefore if these types of initial errors exist in the realistic el nino southern oscillation enso predictions and if a data assimilation or a target method can filter them the enso forecast skill may be improved for ensemble forecast studies different signs of prediction errors caused by the two types of initial errors could illustrate why the ensemble mean offers a better forecast than a single prediction

an air sea coupled skeleton model for the madden julian oscillation this work is an extension and improvement of the minimal madden julian oscillation mjo skeleton model developed by majda and stechmann which can capture some important features of the mjo slow eastward propagation quadrupole vortex structure and independence of frequency on wavelength but is unable to produce unstable growth and selection of eastward propagating planetary waves with the addition of planetary boundary layer frictional moisture convergence these deficiencies can be remedied the frictional boundary layer selects the planetary scale eastward propagation as the most unstable mode but the dynamics remains confined to atmospheric processes only here the authors study the role of air sea interaction by implementing an oceanic mixed layer ml model of wang and xie into the mjo skeleton model in this new air sea coupled skeleton model the features of the original skeleton model remain additionally the air sea interaction under mean westerly winds is shown to produce a strong instability that selectively destabilizes the eastward propagating planetary scale waves although the cloud shortwave radiation seasurfacetemperature crs feedbackdestabilizesbotheastwardand westward modes theair sea feedback associated with the evaporation and oceanic entrainment favors planetary scale eastward modes over the western hemisphere where easterly background winds prevail the evaporation and entrainment feedbacks yield damped modes indicating that longitudinal variation of the mean surface winds plays an important role in regulation of the mjo intensity in addition to the longitudinal variation of the mean sea surface temperature or mean moist static stability this theoretical analysis suggests that accurate simulation of the climatological mean state is critical for capturing the realistic air sea interaction and thus the mjo

simulating the ice thickness distribution in a coupled climate model climate simulations in a global coupled model are investigated using a dynamic thermodynamic sea ice and snow model with sophisticated thermodynamics and a subgrid scale parameterization for multiple ice thicknesses in addition to the sea ice component the model includes a full primitive equation ocean and a simple energy moisture balance atmosphere we introduce a formulation of the ice thickness distribution that is lagrangian in thickness space the method is designed to use fewer thickness categories because it adjusts to place resolution where it is needed most and it is free of diffusive effects that tend to smooth eulerian distributions experiments demonstrate that the model does reasonably well in simulating the mean arctic climate we find the climate of the arctic and northern north atlantic is sensitive to resolving the ice thickness distribution when comparing the model results to a simulation with a two level sea ice model the ice thickness distribution causes ice export through fram strait to be more variable and more strongly linked to meridional overturning in the north atlantic ocean the lagrangian formulation of the ice thickness distribution allows for the inclusion of a vertical temperature profile with relative ease compared to an eulerian method we find ice growth rates and ocean surface salinity differ in our model with a well resolved vertical temperature profile in the ice and snow and an explicit brine pocket parameterization compared to a simulation with semtner zero layer thermodynamics although these differences are important for the climate of the arctic the effects of an ice thickness distribution are more dramatic and extend into the northern north atlantic sensitivity experiments indicate that five ice thickness categories with 50 cm vertical temperature resolution capture the effects of the ice thickness distribution on the heat and freshwater exchange across the surface in the presence of sea ice in these simulations

predictability of a coupled model of enso using singular vector analysis part i optimal growth in seasonal background and enso cycles the fastest initial error growth optimal growth in the zebiak and cane zc forecast model for the el nino southern oscillation enso is analyzed by singular value decomposition of a forward tangent model along a trajectory in a reduced eof space in this paper part i of ii optimal growth about the seasonally varying background and enso cycles from a long model run are discussed among the many forms of nonlinearity in zc the discontinuity of the slope in subsurface temperature at zero thermocline depth and the nonlinear advection of sst are the most significant that positive perturbations grow much faster than negative perturbations around the seasonally varying background is first attributable to the discontinuity and second attributable to nonlinear advection about the seasonally varying background 6 month optimal growth is largest for early boreal spring starts which is related to the enhanced atmospheric heating due to equatorward movement of the itcz one dominant growing structure is found characterized by north south and east west sst dipoles convergent winds on the equator in the eastern pacific and a deepened thermocline in the whole equatorial belt this structure is insensitive to start month and optimization time optimal growth about enso cycles in a long model run is generally much smaller than that about the seasonally varying background as before one dominant growing structure insensitive to start time and optimization time is found during the warm phase of enso optimal growth is modulated by season as is that about the seasonal varying background during the onset and mature phases of enso the final pattern of the optimal structure in 6 months is confined to the eastern pacific during the decay phase of enso it spreads to the western pacific as well during the cold phase of enso optimal growth has two maxima in a year early spring and fall the optimal perturbation propagates westward associated with surface layer wind interaction the authors also compare the singular vector analysis in eof space and the standard one in physical space the importance of norm definition to optimal growth and optimal structure is discussed

oxidation and microprobe induced potassium mobility in iron bearing phyllosilicates from the otago schists new zealand abstract biotite chlorite and stilpnomelane have undergone post metamorphic oxidation in situ in the otago schist due to surficial weathering the oxidation results in changes in the chemistry of these minerals oxidation of biotite and stilpnomelane is accompanied by loss of potassium and stilpnomelane with its full metamorphic potassium content is probably rare analytical work such as k ar dating which depends critically on k 2 o contents of biotite and stilpnomelane should therefore proceed with due caution potassium in stilpnomelane is very mobile under the microprobe beam and only approximate k 2 o analyses may be obtained

drift of pancake ice floes in the winter antarctic marginal ice zone during polar cyclones high temporal resolution in situ measurements of pancake ice drift are presented from a pair of buoys deployed on floes in the antarctic marginal ice zone during the winter sea ice expansion over 9 days in which the region was impacted by four polar cyclones concomitant measurements of wave in ice activity from the buoys are used to infer that the ice remained unconsolidated and pancake ice conditions were maintained over at least the first 7 days analysis of the data shows i the fastest reported ice drift speeds in the southern ocean ii high correlation of drift velocities with the surface wind velocities indicating absence of internal ice stresses 100 km from the ice edge where remotely sensed ice concentration is 100 and iii presence of a strong inertial signature with a 13 hr period a lagrangian free drift model is developed including a term for geostrophic currents that reproduce the 13 hr period signature in the ice motion the calibrated model provides accurate predictions of the ice drift for up to 2 days and the calibrated parameters provide estimates of wind and ocean drag for pancake floes under storm conditions

modeling tropical precipitation in a single column abstract a modified formulation of the traditional single column model for representing a limited area near the equator is proposed this formulation can also be considered a two column model in the limit as the area represented by one of the columns becomes very large compared to the other only a single column is explicitly modeled but its free tropospheric temperature rather than its mean vertical velocity is prescribed this allows the precipitation and vertical velocity to be true prognostic variables as in prior analytical theories of tropical precipitation two models developed by other authors are modified according to the proposed formulation the first is the intermediate atmospheric model of j d neelin and n zeng but with the horizontal connections between columns broken rendering it a set of disconnected column models the second is the column model of n o renno k a emanuel and p h stone in the first model the set of disconnected column models is run with a fixed temperature

the role of the mean state in meridional mode structure and growth abstractthis study uses a simple linear coupled model to investigate the role of the wes feedback and itcz mean states in meridional mode variability optimal structures that maximize transient growth are calculated for mean states characteristic of boreal spring and boreal fall in the tropical atlantic during boreal spring the leading optimal structure is a zonal mode that propagates westward and does not resemble the observed meridional mode in contrast the leading optimal structure during fall is a sea surface temperature sst monopole over the northern hemisphere nh that propagates equatorward and westward and that closely matches meridional mode variability during this season it is found that the boreal fall optimal growth greatly exceeds growth of the corresponding optimal during boreal spring despite the observed boreal spring peak in atlantic meridional mode variance sensitivity studies are used to explore the role of northern or southern hemisphere initial conditions itcz width and itcz

a simple atmospheric model of the local and teleconnection responses to tropical heating anomalies abstract a minimal complexity model of both the local and remote stationary responses of the atmosphere to tropical heating anomalies is described and demonstrated two levels are recast as baroclinic and barotropic components with thermal advection in the tropics neglected the model is linearized about some idealized and realistic background wind fields and forced with a localized heating for illustration in the tropics the baroclinic responses are familiar from the matsuno gill model these excite barotropic responses by advective interactions with vertical background wind shear the barotropic signals are in turn transmitted to high latitudes only in the presence of barotropic background westerly winds for an el nino like equatorial heating the barotropic response has anticyclones to the north and south of the heating reinforcing opposing the anticyclonic cyclonic baroclinic gyres in the upper lower troposphere with realistic background flows the model reproduces the hemispheric asymmetry

phase locking of equatorial atlantic variability through the seasonal migration of the itcz the equatorial atlantic is marked by significant interannual variability in sea surface temperature sst that is phase locked to late boreal spring and early summer the role of the atmosphere in this phase locking is examined using observations reanalysis data and model output the results show that equatorial zonal surface wind anomalies which are a main driver of warm and cold events typically start decreasing in june despite sst and sea level pressure gradient anomalies being at their peak during this month this behavior is explained by the seasonal northward migration of the intertropical convergence zone itcz in early summer the north equatorial position of the atlantic itcz contributes to the decay of wind anomalies in three ways 1 horizontal advection associated with the cross equatorial winds transports air masses of comparatively low zonal momentum anomalies from the southeast toward the equator 2 the absence of deep convection leads to changes in vertical momentum transport that reduce the equatorial wind anomalies at the surface while anomalies aloft remain relatively strong 3 the cross equatorial flow is associated with increased total wind speed which increases surface drag and deposit of momentum into the ocean previous studies have shown that convection enhances the surface wind response to sst anomalies the present study indicates that convection also amplifies the surface zonal wind response to sea level pressure gradients in the western equatorial atlantic where sst anomalies are small this introduces a new element into coupled air sea interaction of the tropical atlantic

the interplay of dynamic and thermodynamic processes in driving the ice edge location in the southern ocean a stand alone sea ice model cice4 was used to investigate the physical processes affecting the ice edge location particular attention is paid to the relative contributions of dynamic and thermodynamic processes in advancing the ice edge equatorward during ice growth results from 10 years of an 11 year numerical simulation have been verified against satellite observations from 1998 to 2007 the autumn advance of the sea ice edge is primarily due to thermodynamic processes with significant dynamic contributions limited to regions such as 60 708 e and 310 3408 e in the dynamically dominated regions winds with a southerly component cause equatorward ice advection but also induce thermodynamic growth of new ice which occurs well poleward of the 15 iceconcentration contour where air temperature is lowest as the ice moves into warmer water it melts hence extending equatorward the region with ocean mixed layer at freezing point this accelerates the northward progression of the ice edge and permits thermodynamic ice growth as soon as the air temperature reaches below the ocean freezing point in regions where thermodynamic processes are dominant e g 340 408 e maximum ice production occurs just poleward of the 15 ice concentration contour where thin sea ice is prevalent in these longitude bands autumn ice melt is generally absent at the ice edge due to ineffective equatorward ice advection

pacific east asian teleconnection part ii how the philippine sea anomalous anticyclone is established during el nino development the anomalous philippine sea anticyclone psac conveys impacts of el nino to east asian climate during the mature and decay of an el nino from the winter to ensuing summer it is shown that the anomalous psac forms in fall about one season prior to the peak el nino its strength increases with the el nino intensity and its sign reverses during a la nina the psac formation concurs with abnormal deepening of the east asian trough and with increasing number of northward recurvature of tropical storms in the western pacific the psac establishment is abrupt coupling with a swing from a wet to dry phase of an intraseasonal oscillation iso and often concurrent with early retreat of the east asian summer monsoon the iso becomes inactive after psac establishment the development of the psac is attributed to combined effects of the remote el nino forcing tropical extratropical interaction and monsoon ocean interaction the developing el nino induces off equatorial as cending rossby wave responses and land surface cooling in northeast asia both deepen the east asian trough in fall and induces vigorous tropical extratropical exchange of air mass and heat which enhances the cold air outbreak and initiation of the psac through exciting descending rossby waves the el nino induced indonesian subsidence generates low level anticyclonic vorticity over south asia which is advected by mean monsoon westerly instigating the anomalous psac the iso interacting with the underlying ocean plays a critical role in the abrupt establishment of psac the wind evaporation entrainment feedback tends to amplify suppress iso before after winter northeasterly monsoon commences suggesting the roles of atmosphere ocean inter action and the seasonal march of background winds in changing the philippine sea iso intensity and maintaining psac

modeling sea ice transport using incremental remapping sea ice models contain transport equations for the area volume and energy of ice and snow in various thickness categories these equations typically are solved with first order accurate upwind schemes which are very diffusive with second order accurate centered schemes which are highly oscillatory or with more sophisticated second order schemes that are computationally costly if many quantities must be transported e g multidimensional positive definite advection transport algorithm mpdata here an incremental remapping scheme originally designed for horizontal transport in ocean models is adapted for sea ice transport this scheme has several desirable features it preserves the monotonicity of both conserved quantities and tracers it is second order accurate except where the accuracy is reduced locally to preserve monotonicity and it efficiently solves the large number of equations in sea ice models with multiple thickness categories and tracers remapping outperforms the first order upwind scheme and basic mpdata scheme in several simple test problems in realistic model runs remapping is less diffusive than the upwind scheme and about twice as fast as mpdata

the influence of atmospheric convection on the interaction between the indian ocean and enso abstractin recent years it has been proposed that a negative positive indian ocean dipole iod in boreal autumn favors an el nino la nina at a lead time of 15 months observational analysis suggests that a negative iod might be accompanied by easterly anomalies over the western pacific such easterlies can enhance the western pacific warm water volume thus favoring el nino development from the following boreal spring onward however a gill model response to a negative iod forcing would lead to nearly zero winds over the western pacific the authors hypothesize that a negative iod or even a cool western indian ocean alone leads to low level air convergence and hence enhanced convectional heating over the maritime continent which in turn amplifies the wind convergence so as to cause easterly winds over the western pacific this hypothesis is tested by coupling an idealized indian ocean model and a convective feedback model over the maritime continent to the zebiak cane model it is found that for a

el nino and la nina abstract el nino and la nina are the two complementary phase of the southern oscillation during e1 nina the area of high sea surface temperatures increases while the atmospheric convection zones of the tropical pacific expand and merge so that there is a tendency toward spatially homogeneous conditions la nina is associated with low sea surface temperatures near the equator with atmospheric convergence zones that are isolated from each other and with spatial wales smaller than those of el nina it is proposed that both phases of the southern oscillation can be attributed to unstable interactions between the tropical ocean and atmosphere during el nina the increase release of latent heat to the atmosphere drives the instability during la nina when the heating of the atmosphere decreases the compression of the convection into smaller and smaller areas permits an instability that intensifies the trade winds and the oceanic currents the unstable air sea interactions are modulated by the seasonal m

a mechanism for decadal changes of enso behavior roles of background wind changes this study explains why a number of el nino properties period amplitude structure and propagation have changed in a coherent manner since the late 1970s and why these changes had almost concurred with the pacific decadal climate shift evidence is presented to show that from the pre shift 1961 1975 to the post shift 1981 1995 epoch significant changes in the tropical pacific are found in the surface winds and temperature whereas changes in the thermocline are uncertain numerical experiments with the cane and zebiak model demonstrate that the decadal changes in the surface winds qualitatively reproduce the observed coherent changes in el nino properties the fundamental factor that altered the model s el nino is the decadal changes of the background equatorial winds and associated upwelling the annual cycle is also necessary for the mean state to modulate el nino from the pre to post shift epoch the changes in the background winds and upwelling modify the structure of the coupled mode eastward displacement of the equatorial westerly anomalies by reallocating anomalous atmospheric heating and sst gradient along the equator this structural change amplifies the enso cycle and prolongs the oscillation period by enhancing the coupled instability and delaying transitions from a warm to a cold state or vice versa the changes in the mean currents and upwelling reduce the effect of the zonal temperature advection while enhance that of the vertical advection thus the prevailing westward propagation is replaced by eastward propagation or standing oscillation our results suggest a critical role of the atmospheric bridge that rapidly conveys the influences of extratropical decadal variations to the tropics and the possibility that the pacific climate shift might have affected el nino properties in the late 1970s by changing the background tropical winds and the associated equatorial upwelling

an investigation of the el nino southern oscillation cycle with statistical models 2 model results we have constructed two sets of linear statistical models for predicting equatorial pacific sea surfaces temperatures ssts from the tropical wind field and from the near global sea level pressure slp field the wind models were constructed to encompass the domains relevant to the forcing of trapped equatorial waves associated with the el nino thus they provide a measure against which the performance of some simple physical models may be compared the slp models were constructed to better define the roles of the observed motion of slp features and changes in the southern oscillation as they relate to subsequent equatorial ssts the wind models were designed to provide forecasts at lead times of 1 to 5 months and the slp models were designed to provide forecasts at lead times of 7 to 16 months the models were constructed using a combination of extended empirical orthogonal functions and canonical correlation analysis a technique we found well suited to the handling of large data sets and the analysis of model structures forecast skills were estimated by cross validation the results show that the wind field models do well at predicting eastern and central pacific ssts during much of the year and their structure is in general agreement with the idea that kelvin rossby waves initiated by remote wind forcing are responsible for much of the observed sst signal however the models do not track the onset of warm and cold events well particularly in the eastern pacific this suggests that well organized consistent wind anomalies are not responsible for the initial temperature anomalies the slp models did not do well in least squares sense but performed skillfully when applied with a simple el nino no el nino decision rule at lead times of up to 16 months

trade wind fluctuations associated with el nino southern oscillation events wind fields associated with el nino southern oscillation enso events are investigated using 20 years 1965 1984 of monthly mean wind vectors along a ship track from 30 s to 30 n in the western pacific ocean the analysis shows that off equatorial trade wind fluctuations play a significant role in enso events in particular the meridional component is found to have strong deviations during enso events southerly deviations from the mean meridional field are noted during the enso events of 1965 1972 1976 and 1982 the trade wind deviations are consistent with atmospheric convergence into an equatorial convection region to the east of the ship track it is hypothesized that these wind fields can cause anomalous oceanic mass convergence toward the equator

enso simulated by intermediate coupled models and evaluated with observations over 1970 98 part i role of the off equatorial variability enso simulations are investigated in 30 yr integrations of various intermediate coupled models and compared with observed sst wind and thermocline depth anomalies over the tropical pacific the cane and zebiak model simulates warm events with a period close to the observations but with westerlies that are located 30 8 east of them and thermocline anomalies in the western pacific that are much shallower between two warm events the model simulates a series of three weak and short cold sst peaks and hardly ever simulates easterlies the sst in the eastern equatorial pacific is not sensitive to thermocline depth anomalies but to the anomalous downwelling of surface currents induced by ekman shear the model simulates a pair of very strong cyclonic wind stress curl anomalies on both sides of the equator in the eastern off equatorial domain between 78 and 158 lat these are necessary to maintain the oscillatory regime so are the ocean meridional rossby modes higher than 5 the thermocline zonal slopes required to balance the off equatorial curl anomalies are about three times steeper than the ones required to balance the zonal stress along the equator thus the off equator exerts an excess of zonal pressure which by continuity affects the equatorial ocean and plays a crucial role in reversing and triggering the growing events six months after the warm peaks the whole ocean between 158s and 158n is significantly upwelled the equatorial oceanic heat content is recharged from the south prior to a warm event contrary to simulations when the model is driven by observed wind anomalies increasing the friction in the baroclinic ocean does not decrease the off equatorial variability but significantly alters the low frequency oscillations that are no longer enso like introducing the parameterization of subsurface temperature derived from hydrographic profiles in the ocean component does not allow the coupled model to recover cold events as in a forced context introducing the parameterization of convection derived from high cloud temperature measurements is the most effective improvement but results still poorly agree with observations and are in contrast with the simulations driven by observed sst biased toward westerlies in the central pacific upwelled thermocline in the west and warm sst in the east thus modifying the ocean component only or the atmosphere only does not have the same impact on simulations as in a forced context the coupling allows new mechanisms to grow and govern the model behavior one of them is the slow meridional oceanic mass adjusment in quasi sverdrup balance with the winds

a simple model of climatological rainfall and vertical motion patterns over the tropical oceans abstract a simple model is developed that predicts climatological rainfall vertical motion and diabatic heating profiles over the tropical oceans given the sea surface temperature sst using statistical relationships deduced from the 40 yr ecmwf re analysis era 40 the model allows for two modes of variability in the vertical motion profiles a shallow mode responsible for all boundary layer convergence between 850 hpa and the surface and a deep mode with no boundary layer convergence the model is based on the argument expressed in the authors companion paper that boundary layer convergence can be usefully viewed as a forcing on deep convection not just a result thereof the shallow mode is either specified from satellite observations or modeled using a simple mixed layer model that has sst as well as 850 hpa geopotential height winds and temperature as boundary conditions the deep mode amplitude is empirically shown to be proportional to a simple measure of conditional instability in conve

estimates of large scale divergence in the lower troposphere over the western equatorial pacific a network of 915 mhz wind profilers measured half hourly lower tropospheric winds over the western equatorial pacific with vertical resolutions as high as 100 m during november 1992 through february 1993 the intensive observing period iop of the tropical ocean global atmosphere coupled ocean atmosphere response experiment toga coare these wind data are used in conjunction with collocated surface wind measurements to examine the near surface divergent flow over the western pacific warm pool during austral summer as well as the synoptic scale variability of divergence in both time and space the synoptic scale wind field estimated from profiler data exhibits stronger near surf ace divergence than sonde based estimates from the same time period temporal variations of the lower tropospheric divergence profiles are described by three vertical structure functions derived from varimax rotated eigenvector analysis one vertical mode appears to be associated with deep convection one with near surface processes and one with shallower convection these structure functions vary zonally across the coare region with the convective modes having convergence maxima at lower elevations to the west of the intensive flux array ifa than over and east of it

modeling the thermodynamics of a sea ice thickness distribution 2 sea ice ocean interactions in this paper we examine the coupling of an ice thickness distribution model with an ocean mixed layer model the annual cycle of the modeled mixed layer temperature salinity and depth are compared to observations from the drifting ice stations of the arctic ice dynamics joint experiment aidjex the role of the ice thickness distribution in determining the ice ocean coupling is examined we find that the ice thickness distribution is important for the exchange of heat salt and fresh water between the ice and the ocean especially with regard to the effects of thin first year ice several different parameterizations of the ice ocean turbulent heat exchange are compared the results indicate that the storage of heat in the ocean mixed layer is an important physical process for determining the annual average ice thickness double diffusion and the stabilizing effects of meltwater also impact the exchange of heat between the ocean and ice cover questions remain as to the relative importance of these processes and their accurate parameterization in ice ocean coupled models

origin of archean anorthosites evidence from the bad vermilion lake anorthosite complex ontario the bad vermilion lake anorthosite complex 2 700 m y is exposed over an area of about 100 km2 near rainy lake ontario as is typical of other archean anorthosites it is composed of coarse 1 30 cm across equidimensional euhedral to subhedral calcic an80 plagioclase in a finer grained mafic matrix the amount of mafic matrix in individual samples ranges from none to about 70 by volume the complex has been variably metamorphosed to greenschist facies zoisite chlorite and hornblende are abundant but primary plagioclase is preserved in many places