on the factors controlling the development of shallow convection in eddy diffusivity mass flux models abstractthis study addresses key aspects of shallow moist convection as simulated by a multiplume eddy diffusivity mass flux edmf model two factors suggested in the literature to be essential f

a combined eddy diffusivity mass flux approach for the convective boundary layer a better conceptual understanding and more realistic parameterizations of convective boundary layers in climate and weather prediction models have been major challenges in meteorological research in particular parameterizations of the dry convective boundary layer in spite of the absence of water phase changes and its consequent simplicity as compared to moist convection typically suffer from problems in attempting to represent realistically the boundary layer growth and what is often referred to as countergradient fluxes the eddy diffusivity ed approach has been relatively successful in representing some characteristics of neutral boundary layers and surface layers in general the mass flux mf approach on the other hand has been used for the parameterization of shallow and deep moist convection in this paper a new approach that relies on a combination of the ed and mf parameterizations edmf is proposed for the dry convective boundary layer it is shown that the edmf approach follows naturally from a decomposition of the turbulent fluxes into 1 a part that includes strong organized updrafts and 2 a remaining turbulent field at the basis of the edmf approach is the concept that nonlocal subgrid transport due to the strong updrafts is taken into account by the mf approach while the remaining transport is taken into account by an ed closure large eddy simulation les results of the dry convective boundary layer are used to support the theoretical framework of this new approach and to determine the parameters of the edmf model the performance of the new formulation is evaluated against les results and it is shown that the edmf closure is able to reproduce the main properties of dry convective boundary layers in a realistic manner furthermore it will be shown that this approach has strong advantages over the more traditional countergradient approach especially in the entrainment layer as a result this edmf approach opens the way to parameterize the clear and cumulus topped boundary layer in a simple and unified way

the structure of west antarctica from geophysical studies the subglacial topographical and geological configurations of west antarctica and the boundary zone between east and west antarctica are poorly known yet they are crucial to our understanding of the tectonic evolution of the pacific proto atlantic margin of gondwanaland preliminary results are presented of simultaneous airborne radio echo and magnetic sounding of 106 km2 of west antarctica including detailed maps of ice sheet and bedrock surfaces magnetics radio echo and other available geophysical data suggest interpretations of sub glacial geology

on postglacial sea level summary an exact method is presented for calculating the changes in sea level that occur when ice and water masses are rearranged on the surface of elastic and viscoelastic non rotating earth models the method is used to calculate the instantaneous elastic and delayed vi scoelastic sea level changes following the partial melting of late quaternary ice sheets we find that there can be large errors in the usual assumption that changes in sea level are uniform over the ocean basins if a quantity of ice equivalent to a uniform 100 m rise in sea level melts from the laurentide and fennoscandian ice sheets then in the south pacific the instantaneous rise in sea level can be as large as 120m in the north atlantic the instantaneous rise is always less than 100 m there is a zone in the north atlantic with almost no sea level change and near greenland and norway the sea level falls rather than rises by over 100 m one thousand years after the melting a forebulge migrating towards the ice loads causes water to flow from the south pacific into the north pacific suggesting that raised beaches should occur in the south pacific the gravitational attraction of an ice mass upon a nearby ocean tends to hold sea level high in the vicinity of the ice this extra load near the ice may have a significant influence on postglacial isostatic adjustment

a dual mass flux framework for boundary layer convection part i transport abstract this study considers the question of what is the least complex bulk mass flux framework that can still conceptually reproduce the smoothly varying coupling between the shallow convective cloud layer and the subcloud mixed layer to this end the model complexity of the classic single bulk mass flux scheme is enhanced inspired by recent large eddy simulation results the authors argue that two relatively minor but key conceptual modifications are already sufficient to achieve this goal i retaining a dry transporting updraft in the moist limit and ii applying continuous updraft area partitioning to this dual mass flux dualm framework the dry updraft represents all internal mixed layer updrafts that terminate near the mixed layer top whereas the moist updraft represents all updrafts that condense and rise out of the mixed layer as buoyant cumulus clouds the continuous area partitioning between the dry and moist updraft is a function of moist convective inhibition above the mixed layer top

regime of the filchner ronne ice shelves antarctica seismic radio echo twerle balloon and oceanographic data of the filchner ronne ice shelves are analysed a large thin area in the central ronne ice shelf is found to differ from the morphology of the ross and filchner ice shelves this area is partly filled by basal saline ice which can be attributed to regional regelation caused by oceanic circulation

deglacial hypsometry of antarctica abstract a new and more detailed analysis of the hypsometry of the antarctic continent based upon 1 digital data on ice thickness and surface and subglacial elevations shows that antarctica even when deglaciated according to a simple airy isostatic model is an unusual continent it is the only one with a markedly bimodal hypsometric curve and separation of the two modes shows that they are the single modes of west antarctica at 450 m a s 1 and east antarctica at 950 m a s 1 respectively the two parts of the continent are probably distinct tectonic entities the modal height of east antarctica is 700 m higher than that of the global ensemble of continents suggesting that hotspot epeirogeny or a less well known mechanism has affected its recent history the age of this modal height anomaly has important tectonic and especially climatic implications it is equivalent to a 4 6 c cooling of the continental surface the area of dry land after deglaciation is 10 5 10 6 km 2 the volume of ice in antarctica is estimated at 26 9 10 6 km 3 and of ice in the northern hemisphere at 2 5 10 6 km 3 these figures lead to a eustatic sea level equivalent for present day glacier ice of 68 m or somewhat less

large eddy simulation of the diurnal cycle of shallow cumulus convection over land summary large eddy simulations of the development of shallow cumulus convection over land are presented many characteristics of the cumulus layer previously found in simulations of quasi steady convection over the sea are found to be reproduced in this more strongly forced unsteady case furthermore the results are shown to be encouragingly robust with similar results obtained with eight independent models and also across a range of numerical resolutions the datasets produced are already being used in the development and evaluation of parametrizations used in numerical weather prediction and climate models

modeling entrainment and finescale mixing in cumulus clouds abstract a model used to study entrainment and mixing of thermodynamic properties in the stratus topped boundary layer has been extended to represent these processes in cumulus clouds the new model called the explicit mixing parcel model empm depicts finescale internal structure of a rising thermal in a cumulus cloud using a 1d domain the empm links the conventional parcel model which has no internal structure and multidimensional cloud models which resolve cloud scale structure produced by large eddies in the empm the internal structure evolves as a consequence of a sequence of discrete entrainment events and an explicit representation of turbulent mixing based on kerstein s linear eddy model in this version of the empm subgrid scale eddy diffusion is found to be adequate for representing the effects of the smallest turbulent eddies in addition a simple parameterization is used to determine the local condensation or evaporation rates if the grid size is reduced so that the kolmogorov

a scale adaptive turbulent kinetic energy closure for the dry convective boundary layer abstracta pragmatic scale adaptive turbulent kinetic energy tke closure is proposed to simulate the dry convective boundary layer for a variety of horizontal grid resolutions from 50 m typical of large eddy simulation models that use three dimensional turbulence parameterizations closures up to 100 km typical of climate models that use one dimensional turbulence and convection parameterizations closures since parameterizations closures using the tke approach have been frequently used in these two asymptotic limits a simple method is proposed to merge them with a mixing length scale formulation for intermediate resolutions this new scale adaptive mixing length naturally increases with increasing grid length until it saturates as the grid length reaches mesoscale model resolution the results obtained using this new approach for dry convective boundary layers are promising the mean vertical profiles of potential temperature and heat flux remain in good agreement for different resolutions a contin

investigating the scale adaptivity of a size filtered mass flux parameterization in the gray zone of shallow cumulus convection abstractin this study the scale adaptivity of a new parameterization scheme for shallow cumulus clouds in the gray zone is investigated the eddy diffusivity multiple mass flux ed mf n scheme is

a thermal plume model for the convective boundary layer representation of cumulus clouds abstract the thermal plume model a mass flux scheme combined with a classical diffusive approach originally developed to represent turbulent transport in the dry convective boundary layer is extended here to the representation of cloud processes the modified parameterization is validated in a 1d configuration against results of large eddy simulations les as well as in a 3d configuration against in situ measurements for a series of cases of dry and cloudy convective boundary layers accounting for coherent structures of the mixed layer with the mass flux scheme improves the representation of the diurnal cycle of the boundary layer particularly its progressive deepening during the day and the associated near surface drying results also underline the role of the prescription of the mixing of air between the plume and its environment and of submean plume fluctuations

a multiple mass flux parameterization for the surface generated convection part i dry plumes abstract the present study introduces a parameterization for the mixing in the surface generated free convection regime including dry and moist convection cases the parameterization explicitly represents the plumes that drive the convective turbulence ascending parcels that have similar properties in the surface layer are grouped into updrafts with a determined fractional area the updrafts ascend according to an entraining plume model and may eventually overturn the plume model can either use a time or a length scale for the lateral entrainment closure the plumes environment is assumed to be horizontally uniform a one dimensional framework is used to evaluate the parameterization in the case of a dry convective boundary layer cbl the predicted variances are underestimated presumably due to the uniform environment assumption the contrast between the strong upward motions and the compensating subsidence is simulated and the skewness of w increases realistically with height the plumes dyn

a multiple mass flux parameterization for the surface generated convection part ii cloudy cores abstract the multiple mass flux approach introduced in a companion paper aims at parameterizing the surface generated convection in the atmosphere the original aspects of this model are as follows a number of convective updrafts are released in the surface layer they initially have distinct fractional area and thermodynamic properties determined through surface layer similarity that is by assuming that the thermodynamic fluxes are constant throughout the surface layer each updraft ascent is diagnosed using an entraining plume model in the case of cumulus convection this comprehensive formulation provides consistent representations of the subcloud mixing the cloud mixing and the associated cloudiness in the present paper this model is evaluated in two shallow moist convection cases using the one dimensional modeling framework in the continental convection case the diurnal cloud growth and the related subcloud layer ventilation agree with large eddy simulations in the oceanic convection cas

a unified eddy diffusivity mass flux approach for modeling atmospheric convection abstracta fully unified parameterization of boundary layer and moist convection shallow and deep is presented the new parameterization is based on the stochastic multiplume eddy diffusivity mass

a dual mass flux framework for boundary layer convection part ii clouds this paper presents the extension of the eddy diffusivity mass flux edmf framework for turbulent transport into the statistical modeling of boundary layer clouds the advection diffusion decomposition that defines edmf is projected onto the turbulent distribution as used in the statistical cloud model each edmf component is thus assigned its own independent probability density function pdf resulting in an updraft pdf and a diffusive pdf this double pdf system is configured and integrated in conserved variable space with the position and orientation of each pdf determined by its unique nature the parameterization of the associated updraft diffusion decomposition of variance introduces close ties to the transport scheme whereas the grid box mean variance is reconstructed using a prognostic variance budget the variance of the updraft component is parameterized as a function of the spread among various resolved model updrafts individual model components and the scheme as a whole are evaluated in detail against large eddy simulations of a number of prototype subtropical trade wind cases the results show that various structures in cloud fraction condensate and variance are reproduced the diffusive pdf acts to represent stratiform clouds the advective pdf represents cumuliform clouds in conditionally unstable layers this allows representation of complex scenarios in which both cloud forms occur such as the transitional trade wind regime featuring cumulus rising into stratocumulus

tidal and subtidal exchange flows at an inlet of the wadden sea abstract observations of underway velocity profiles during complete spring and neap tidal cycles were used to determine whether the spatial structures of tidal and subtidal flows at a tidal inlet in a multiple inlet embayment are consistent with those observed at single inlet embayments measurements were obtained at the otzumer balje one of the multiple inlets among the east frisian islands of the wadden sea the 1 5 km wide inlet displayed a bathymetric profile consisting of a channel 15 m deep flanked by