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

the atmospheric boundary layer and the gray zone of turbulence a critical review recent increases in computing power mean that atmospheric models for numerical weather prediction are now able to operate at grid spacings of the order of a few hundred meters comparable to the dominant turbulence length scales in the atmospheric boundary layer as a result models are starting to partially resolve the coherent overturning structures in the boundary layer in this resolution regime the so called boundary layer gray zone neither the techniques of high resolution atmospheric modeling a few tens of meters resolution nor those of traditional meteorological models a few kilometers resolution are appropriate because fundamental assumptions behind the parameterizations are violated nonetheless model simulations in this regime may remain highly useful in this paper a newly formed gray zone boundary layer community lays the basis for parameterizing gray zone turbulence identifies the challenges in high resolution atmospheric modeling and presents different gray zone boundary layer models we discuss both the successful applications and the limitations of current parameterization approaches and consider various issues in extending promising research approaches into use for numerical weather prediction the ultimate goal of the research is the development of unified boundary layer parameterizations valid across all scales

performance of an eddy diffusivity mass flux scheme for shallow cumulus boundary layers comparisons between single column scm simulations with the total energy mass flux boundary layer scheme temf and large eddy simulations les are shown for four cases from the gulf of mexico atmospheric composition and climate study gomaccs 2006 field experiment in the vicinity of houston texas the scm simulations were run with initial soundings and surface forcing identical to those in the les providing a clean comparison with the boundary layer scheme isolated from any other influences good agreement is found in the simulated vertical transport and resulting moisture profiles notable differences are seen in the cloud base and in the distribution of moisture between the lower and upper cloud layer by the end of the simulations temf has dried the subcloud layer and moistened the lower cloud layer more than les temf gives more realistic profiles for shallow cumulus conditions than traditional boundary layer schemes which have no transport above the dry convective boundary layer changes to the formulation and its parameters from previous publications are discussed

propagation characteristics of extratropical planetary waves observed in the atsr global sea surface temperature record this paper examines the characteristics of planetary wave signatures that have been found in the along track scanning radiometer averaged sea surface temperature asst record for 1991 1996 longitude time plots for every latitude between 5 and 50 north and south reveal westward propagating wave like patterns at many locations whose speed decreases with latitude like baroclinic rossby waves a two dimensional radon transform method is used to measure the wave speed and its variation with location and time which broadly matches the rossby wave speeds predicted by the most recent theory and those measured by topex altimetry although there are some discrepancies at low latitudes the thermally detected speeds are slower than expected a possible consequence of sampling limitations wave signatures are clearest between 25 and 40 s where the meridional temperature gradient is strongest here observed speeds are 20 30 greater than theoretical predictions planetary wave speed varies considerably with longitude in general it increases toward the west of ocean basins and distinct differences between ocean basins are evident the propagation characteristics of the waves appear to change abruptly at locations consistent with latitudinal variations in seafloor bathymetry particularly midocean ridges in addition eastward propagating signatures are found in the southern ocean the results demonstrate the value of the asst data set as a tool for studying basin scale wave processes as a complement to the use of altimetry by observing the thermal signature of rossby waves the method has the potential to clarify their influence on air sea interaction processes and to contribute to climate modeling studies

coupled dynamics of earth s geomagnetic westward drift and inner core super rotation this phd work focuses on the rotational dynamics of the coupled inner core outercore mantle system the conservation of the angular momentum our coupled earth model indeed involves two direct electromagnetic torques at the fluid core boundaries and a remote gravitational torque between the inner core and the mantle the rotational dynamics is described by four typical shears and studied in convective numerical simulations of the geodynamo which are able to reproduce the main characteristics of the geomagnetic field and its secular variation this secular variation is mainly embodied by the westward drift of magnetic flux patches at the cmb concentrated on the equator of the atlantic hemisphere and is well documented for the last four centuries we provide constrains on the inner core differential rotation by expressing its link to the geomagnetic westward drift this is performed through the formulation and the validation of dynamical electromagnetic torque models which are then introduced in the conservation of the angular momentum of the system in the long term state the global shear in the fluid outer core is distributed between the westward drift and the differential rotation of the inner core in proportions controlled by the state of couplings as a present day estimate of this shear is close to the observed westward drift we conclude there is no differential rotation of the inner core on time average in the time dependent state we observed that the strength of gravitational coupling is the dominant parameter this places limit on the decadal fluctuations of the inner core differential rotation which should not exceed a few hundredths of degree per year

on the latitude dependence of drift velocity of the geomagnetic main field and its secular variation abstract there is an apparent difference in the westward drift between the geomagnetic main field and its time derivative secular variation the drift velocity of the main field is about 0 2 year definitely lower than that of the secular variation 0 3 year the drift velocity of the main field appears to change with latitude being low at high latitudes and higher at low latitudes whereas the velocity of the secular variation is nearly constant irrespective of latitude this paper examines what causes this difference by adopting the drifting and standing field model that assumes the geomagnetic field consists of the field steadily drifting westwards and the field remaining at nearly the same location in this study we confirm that the existence of the non drifting standing field significantly affects the estimate of the drift velocity of the total field i e the main field and makes it slower than that of the secular variation the drifting field is intense in low latitudes with its maximum at the equator while the standing field dominates in higher latitudes as a consequence reduction of the apparent drifting velocity of the total field by the standing field is conspicuous in higher latitudes and less so in low latitudes this creates the observed latitudinal structure of the drift velocity of the main field on the other hand the drift velocity of the secular variation is less affected by existence of the standing field and mostly reflects the velocity of the drifting field that is almost constant with latitude the velocity of the secular variation thus becomes almost uniform independent of latitude the observed difference between the main field and the secular variation is naturally derived from the drifting and standing field model this implies that physical mechanisms to generate the drifting and standing fields can be considered independently

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

emergence and evolution of the south atlantic anomaly revealed by the new paleomagnetic reconstruction shawq2k abstract the south atlantic anomaly saa is one of the most outstanding features of the present geomagnetic field thus a good knowledge of the saa is clue for a better understanding of the dynamical behavior of the geomagnetic field to achieve this goal paleomagnetic data are crucial since they provide the unique way to investigate past changes in the earth s magnetic field here we present a new global geomagnetic field reconstruction the shawq2k model which is based on a critical revision of the global archeomagnetic and volcanic dataset the new model provides an improved description of the geomagnetic field during the last 2 millennia and yields surprising outcomes about the emergence and development of the saa it shows that the reversed flux patch observed at the core mantle boundary and linked to the saa emerged in the southern hemisphere from at least 950 ad this patch moved westward from the equator to southern latitudes being clearly isolated after 1400 ad in addition since 1550 ad a second reversed flux patch moving northeastward is observed in the north atlantic the new data now available for the southern hemisphere coming from africa and south america together with the use of an appropriated weighting scheme in the modeling process have improved our understanding of past geomagnetic field behavior and showed new evolutionary aspects of the saa

seamless stratocumulus simulation across the turbulent gray zone abstracta pragmatic approach for representing partially resolved turbulence in numerical weather prediction models is introduced and tested the method blends a conventional boundary layer parameterization suitable for large grid lengths with a subgrid turbulence scheme suitable for large eddy simulation the key parameter for blending the schemes is the ratio of grid length to boundary layer depth the new parameterization is combined with a scale aware microphysical parameterization and tested on a case study forecast of stratocumulus evolution simulations at a range of model grid lengths between 1 km and 100 m are compared to aircraft observations the improved microphysical representation removes the correlation between precipitation rate and model grid length while the new turbulence parameterization improves the transition from unresolved to resolved turbulence as grid length is reduced

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

convectively induced secondary circulations in fine grid mesoscale numerical weather prediction models abstractmesoscale numerical weather prediction models using fine grid o 1 km meshes for weather forecasting environmental assessment and other applications capture aspects of larger than grid mesh size convectively induced secondary circulations ciscs such as cells and rolls that occur in the convective planetary boundary layer pbl however 1 km grid spacing is too large for the simulation of the interaction of ciscs with smaller scale turbulence the existence of ciscs also violates the neglect of horizontal gradients of turbulent quantities in current pbl schemes both aspects poorly resolved ciscs and a violation of the assumptions behind pbl schemes are examples of what occurs in wyngaard s terra incognita where horizontal grid spacing is comparable to the scale of the simulated motions thus model ciscs m ciscs cannot be simulated reliably this paper describes how the superadiabatic layer in the lower convective pbl together with increased horizontal resolution allow the critical ra

sticky thermals evidence for a dominant balance between buoyancy and drag in cloud updrafts abstractthe vertical velocities of convective clouds are of great practical interest because of their influence on many phenomena including severe weather and stratospheric moistening however the magnitudes of forces giving rise to these vertical velocities are poorly understood and the dominant balance is in dispute here an algorithm is used to extract thousands of cloud thermals from a large eddy simulation of deep and tropical maritime convection using a streamfunction to define natural boundaries for these thermals the dominant balance in the vertical momentum equation is revealed cloud thermals rise with a nearly constant speed determined by their buoyancy and the standard drag law with a drag coefficient of 0 6 contrary to suggestions that cloud thermals might be slippery with a dominant balance between buoyancy and acceleration cloud thermals are found here to be sticky with a dominant balance between buoyancy and drag

simple models of fluid flow at the core surface derived from geomagnetic field models summary we examine the problem of determining the fluid flow at the core surface given a model of the temporal variation of the magnetic field seeking to fit the field over a finite time interval the flow is assumed steady over the time interval and we adopt the frozen flux approximation we produce a range of solutions of varying complexity and subject to different constraints estimate the errors on the solutions and assess their consistency with the underlying assumptions we find both direct evidence for ageostrophic flow in the form of flow across the geographical equator and indirect evidence in the form of poorer fits to the field when the flow is contained to be geostrophic on account of this evidence we do not adopt the geostrophic approximation however we find that unconstrained flows are poorly determined and consider the various alternatives for producing better determined solutions we choose to restrict our attention to determining the large scale toroidal part of the flow and find a simple pattern of flow which is nearly symmetric about the equator from a sequence of maps of the flow over 5 year time intervals back to 1915 we are still able to identify many of the basic aspects of this simple pattern but changes in the flow pattern are discernible although our models of the flow explain a large proportion of the signal typically 95 per cent of the variance the fits which we obtain are not as good as might be expected failure of the underlying assumptions together with our decision to map only the large scale toroidal part of the flow explains the poorer than expected fit

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

a unified convection scheme unicon part i formulation abstractthe author develops a unified convection scheme unicon that parameterizes relative i e with respect to the grid mean vertical flow subgrid vertical transport by nonlocal asymmetric turbulent eddies unicon is a process based model of subgrid convective plumes and mesoscale organized flow without relying on any quasi equilibrium assumptions such as convective available potential energy cape or convective inhibition cin closures in combination with a relative subgrid vertical transport scheme by local symmetric turbulent eddies and a grid scale advection scheme unicon simulates vertical transport of water species and conservative scalars without double counting at any horizontal resolution unicon simulates all dry moist forced free and shallow deep convection within a single framework in a seamless consistent and unified way it diagnoses the vertical profiles of the macrophysics fractional area plume radius and number density as well as the microphysics production and evaporati

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

the convective boundary layer in the terra incognita numerical simulations of a convective boundary layer cbl are performed to investigate model behavior in the terra incognita also known as the gray zone the terra incognita of the cbl refers to a range of model grid spacing that is comparable to the size of the most energetic convective eddies which are on the order of the boundary layer depth using the rayleigh benard thermal instability as reference a set of idealized simulationsisused toshow that grayzone modelingisnot onlya numericalchallenge but also poses dynamical difficulties when the grid spacing falls within the cbl gray zone grid dependent convection can occur the size of the initial instability structures is set by the grid spacing rather than the natural state of the flow this changes higher order flow statistics and poses fundamental difficulties for gray zone modeling applications

equatorially dominated magnetic field change at the surface of earth s core slow temporal variations in earth s magnetic field originate in the liquid outer core we analyzed the evolution of nonaxisymmetric magnetic flux at the core surface over the past 400 years we found that the most robust feature is westward motion at 17 kilometers per year in a belt concentrated around the equator beneath the atlantic hemisphere surprisingly this motion is dominated by a single wavenumber and persists throughout the observation period this phenomenon could be produced by an equatorial jet of core fluid by hydromagnetic wave propagation or by a combination of both discrimination between these mechanisms would provide useful constraints on the dynamics of earth s core

rapidly changing flows in the earth s core variations in the earth s magnetic field over a span of a few months can be resolved despite the potential filtering effects of the electrically conducting mantle and are indicative of rapid flow in the earth s outer core

a comprehensive mass flux scheme for cumulus parameterization in large scale models abstract observational studies indicate that a mass flux approach may provide a realistic framework for cumulus parameterization in large scale models but this approach through the introduction of a spectral cloud ensemble leads normally to rather complex schemes in this paper the question is addressed whether much simpler schemes can already provide realistic values of the thermal forcing by convection under various synoptic conditions this is done through verifying such a scheme first on data from field experiments for periods of tropical penetrative convection gate marshall islands tradewind cumuli atex bomex and extratropical organized convection sesame 79 and then in a nwp model the scheme considers a population of clouds where the cloud ensemble is described by a one dimensional bulk model as earlier applied by yanai et al in a diagnostic study of tropical convection cumulus scale downdrafts are included various types of convection are represented i e penetrative convection in c

geomagnetic secular variation we analyse over 175000 magnetic observations from an interval spanning 1695 1980 to produce a sequence of maps of the magnetic field at the core mantle boundary we find that even the earlier data enable us to determine reliable maps we produce these maps at approximately 60 year intervals through the eighteenth and nineteenth centuries and at 10 year intervals in the twentieth century this span of maps is long enough to render straightforward the distinction between static and drifting features in the field we observe that some features show no sign whatsoever of drift over the entire 285 year time interval although others drift westwards in particular we observe that the secular variation is very low beneath the pacific ocean but beneath southern africa and the south atlantic ocean we observe rapid secular variation we interpret the morphology of the static field in terms of a simple model of the dynamo and conjecture that interactions between the core and the mantle are an important element of the process as part of the static field we identify four main concentrations of flux two in each hemisphere at high latitudes these features largely account for the earth s axial dipole moment we find unequivocal evidence that magnetic flux has not remained frozen over the time span of our models much of the diffusive behaviour that we identify is associated with the formation of a pair of flux spots a core spot beneath southern africa early in this century nevertheless we are able to construct maps that satisfy a set of necessary conditions for frozen flux and use these maps to construct maps of the core surface fluid flow based on the steady flow hypothesis although we find no strong evidence against the steady flow hypothesis we do find some grounds on which to doubt the validity of the flow maps

evolution of calcrete in palaeodrainages of the lake napperby area central australia abstract carbonate lithofacies developed along the trunk valley of palaeodrainage channels as well as those adjacent to gypsite facies in the lake napperby drainage basin in central australia show wide ranges of sedimentary characteristics reflecting significant variation in depositional environments sedimentological and geochemical characterization of the calcrete lithofacies in this drainage area indicate that whereas variations in bedrock morphology are important in overall distribution of the phreatic and vadose calcrete varieties faulting and basin adjustments since the early quaternary may also have played a significant role in redistribution of the hydrologic zones and hence the evolution of these calcretes accordingly phreatic calcretes which initially precipitated from laterally moving groundwaters along the palaeodrainage channels undergo systematic mineralogical changes due to direct evaporative precipitation and diagenetic displacement replacement processes mainly dolomitization and silicification under present hydro chemical conditions within the zone of grounwater fluctuations however lateral and downward shifts in groundwater flow due to excessive volumetric expansion and reduction in effective permeability of calcrete may ultimately result in isolation of the calcrete like those observed from the eastern margins of the lake the evolution of the vadose calcretes is thereafter topographically controlled and relates to mobilization and redistribution of earlier deposited calcretes under present meteorological conditions