Convective-scale perturbation growth across the spectrum of convective regimes

Convection-permitting ensembles have led to improved forecasts of many atmospheric phenomena. However, to fully utilize these forecasts the dependence of predictability on synoptic conditions needs to be understood. In this study, convective regimes are diagnosed based on a convective timescale which identifies the degree to which convection is in equilibrium with the large-scale forcing. Six convective cases are examined in a convection-permitting ensemble constructed using the Met Office Unified Model. The ensemble members were generated using small-amplitude buoyancy perturbations added into the boundary layer, which can be considered to represent turbulent fluctuations close to the gridscale. Perturbation growth is shown to occur on different scales with an order of magnitude difference between the regimes (O(1 km) for cases closer to non-equilibrium convection and O(10 km) for cases closer to equilibrium convection). This difference reflects the fact that cell locations are essentially random in the equilibrium events after the first 12 h of the forecast, indicating a more rapid upscale perturbation growth compared to the non-equilibrium events. Furthermore, large temporal variability is exhibited in all perturbation growth diagnostics for the nonequilibrium regime. Two boundary condition driven cases are also considered and show similar characteristics to the non-equilibrium cases, implying that caution is needed to interpret the timescale when initiation is not within the domain. Further understanding of perturbation growth within the different regimes could lead to a better understanding of where ensemble design improvements can be made beyond increasing the model resolution and could improve interpretation of forecasts

(Nieblas radiactivas, ondas de gravedad y sus interacciones con la turbulencia en la capa límite atmosférica)

Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Físicas, Departamento de Física de la Tierra, Astronomía y Astrofísica I, leída el 17-12-2015Esta tesis aborda el estudio de dos fenómenos atmosféricos que aparecen normalmente en la capa límite estable (SBL): nieblas radiativas y ondas de gravedad (GWs). Estos procesos no están bien comprendidos y por lo tanto su representación en los modelos numéricos es uno de los desafíos a los que se enfrenta la modelización meteorológica futura. De esta forma, el principal objetivo de esta tesis es ampliar el conocimiento sobre estos fenómenos, con un enfoque especial a sus interacciones con la turbulencia en la SBL. El trabajo comienza con experimentos de sensibilidad del modelo WRF (Weather Research and Forecasting) para la determinación de las opciones físicas más apropiadas para la predicción de nieblas. Posteriormente, se aborda la predicción de nieblas a través de dos enfoques diferentes: modelización numérica directa (WRF) y métodos estadísticos (M14, Menut et al. (2014)). Estos dos métodos son evaluados y comparados en dos centros experimentales diferentes. Por otro lado, se presenta una climatología estadística robusta con el objetivo de señalar las diferencias más importantes entre las nieblas radiativas en ambos sitios. Finalmente, se ofrecen nuevos métodos para la estimación de la altura del tope de la niebla. Esta variable es normalmente desconocida o está sujeta a la disponibilidad de datos de difícil adquisición. La estimación que se ofrece en esta tesis se basa en medidas superficiales de turbulencia (velocidad de fricción y flujo de calor). Con respecto a las GWs, por un lado se presenta un análisis observacional único de GWs casi monocromáticas propagadas en un canal, siendo difícil tener la oportunidad de analizar observacionalmente un caso como éste. Por otro lado, se muestran los mecanismos físicos que gobiernan GWs de menor escala y flujos de drenaje, analizando en detalle las interacciones de estos fenómenos con la turbulencia en la SBL, tema que es uno de los actuales desafíos de los estudios micrometeorológicos.This thesis deals with the study of two atmospheric phenomena that normally appear in the stable boundary layer (SBL): radiation fog and gravity waves (GWs), processes that are still not well understood. Therefore, their representation in the numerical weather prediction (NWP) models is one of the current challenges for the meteorological modelling. Thus, the main objective of this thesis is to gain knowledge about these phenomena, with especial emphasis to their interactions with turbulence in the SBL. The work starts with sensitivity experiments of the WRF (Weather Research and Forecasting) mesoscale model, in order to determine the most appropriate physical options for the simulation of fog. Subsequently, radiationfog forecasting is addressed through two different approaches: numerical modelling (WRF) and statistical methods (M14, Menut et al. (2014)). These two methods are evaluated and compared at two contrasting experimental sites. Finally, new methods for the fog-top height estimation are presented. This variable is usually unknown or subjected to expensive or not-always accessible data. The estimation offered in this thesis is based on turbulent surface measurements (friction velocity and heat flux). Regarding GWs, on the one hand, a comprehensive observational analysis of near-monochromatic GWs propagated in a duct layer is presented, being difficult to have the chance of analysing a case like this in the real atmosphere. On the other hand, the physical mechanisms governing smaller-scale GWs and drainage flows are elucidated, analysing in detail the interactions of these phenomena with the turbulence in the SBL, which is one of the main current challenges in micrometeorological studiesDepto. de Física de la Tierra y AstrofísicaFac. de Ciencias FísicasTRUEunpu

Simulations of an observed elevated mesoscale convective system over southern England during CSIP IOP 3

Simulations of an elevated mesoscale convective system (MCS) observed over southern England during the Convective Storm Initiation Project (CSIP) provide the first detailed modelling study of a case of elevated convection occurring in the UK. The study shows that many factors can influence the maintenance of elevated deep convection, from large-scale flow through to surface heating processes and diabatic cooling within the convective system. It is also shown that interactions and feedback mechanisms between a stable layer and the storm can act to maintain deep convection. The simulation successfully reproduced an elevated MCS above a low-level stable undercurrent, with a wave in the undercurrent linked to a rear-inflow jet (RIJ). Convection was fed from an elevated (840hPa) source layer with CAPE of about 350Jkg-1. The undercurrent in the simulation was approximately 1km deep, about half that observed. Unlike the observed MCS, a transition from elevated to surface-based convection occurred in the simulation due to the combined effects of a pre-existing large-scale θe gradient, advection and surface heating causing the system to encounter increasingly unstable low-level air and a shallower stable layer that was more susceptible to penetration by downdraughts. The transition to surface-based convection was accompanied by the development of cold-pool outflow and an increase in system velocity from about 6 to 10ms-1. Diabatic cooling from microphysical processes in the simulation enhanced the undercurrent and strengthened the RIJ. This strengthened the wave in the undercurrent and led to more extensive convection. The existence of a positive feedback process between the convection, RIJ and stable layer is discussed. Uncertainty in the synoptic scale generating errors in the undercurrent is shown to be a major source of error for convective-scale forecasts

Growth behavior of human adipose tissue-derived stromal/stem cells at small scale : numerical and experimental investigations

Human adipose tissue-derived stromal/stem cells (hASCs) are a valuable source of cells for clinical applications, especially in the field of regenerative medicine. Therefore, it comes as no surprise that the interest in hASCs has greatly increased over the last decade. However, in order to use hASCs in clinically relevant numbers, in vitro expansion is required. Single-use stirred bioreactors in combination with microcarriers (MCs) have shown themselves to be suitable systems for this task. However, hASCs tend to be less robust, and thus, more shear sensitive than conventional production cell lines for therapeutic antibodies and vaccines (e.g., Chinese Hamster Ovary cells CHO, Baby Hamster Kidney cells BHK), for which these bioreactors were originally designed. Hence, the goal of this study was to investigate the influence of different shear stress levels on the growth of humane telomerase reversed transcriptase immortalized hASCs (hTERT-ASC) and aggregate formation in stirred single-use systems at the mL scale: the 125 mL (= SP100) and the 500 mL (= SP300) disposable Corning® spinner flask. Computational fluid dynamics (CFD) simulations based on an Euler⁻Euler and Euler⁻Lagrange approach were performed to predict the hydrodynamic stresses (0.06⁻0.87 Pa), the residence times (0.4⁻7.3 s), and the circulation times (1.6⁻16.6 s) of the MCs in different shear zones for different impeller speeds and the suspension criteria (Ns1u, Ns1). The numerical findings were linked to experimental data from cultivations studies to develop, for the first time, an unstructured, segregated mathematical growth model for hTERT-ASCs. While the 125 mL spinner flask with 100 mL working volume (SP100) provided up to 1.68.10⁵ hTERT-ASC/cm² (= 0.63 × 10⁶ living hTERT-ASCs/mL, EF 56) within eight days, the peak living cell density of the 500 mL spinner flask with 300 mL working volume (SP300) was 2.46 × 10⁵ hTERT-ASC/cm² (= 0.88 × 10⁶ hTERT-ASCs/mL, EF 81) and was achieved on day eight. Optimal cultivation conditions were found for Ns1u < N < Ns1, which corresponded to specific power inputs of 0.3⁻1.1 W/m³. The established growth model delivered reliable predictions for cell growth on the MCs with an accuracy of 76⁻96% for both investigated spinner flask types

Assured crew return vehicle post landing configuration design and test

The 1991-1992 senior Mechanical and Aerospace Engineering Design class continued work on the post landing configurations for the Assured Crew Return Vehicle (ACRV) and the Emergency Egress Couch (EEC). The ACRV will be permanently docked to Space Station Freedom fulfilling NASA's commitment of Assured Crew Return Capability in the event of an accident or illness aboard Space Station Freedom. The EEC provides medical support and a transportation surface for an incapacitated crew member. The objective of the projects was to give the ACRV Project Office data to feed into their feasibility studies. Four design teams were given the task of developing models with dynamically and geometrically scaled characteristics. Groups one and two combined efforts to design a one-fifth scale model for the Apollo Command Module derivative, an on-board flotation system, and a lift attachment point system. This model was designed to test the feasibility of a rigid flotation and stabilization system and to determine the dynamics associated with lifting the vehicle during retrieval. However, due to priorities, it was not built. Group three designed a one-fifth scale model of the Johnson Space Center (JSC) benchmark configuration, the Station Crew Return Alternative Module (SCRAM) with a lift attachment point system. This model helped to determine the flotation and lifting characteristics of the SCRAM configuration. Group four designed a full scale EEC with changeable geometric and geometric and dynamic characteristics. This model provided data on the geometric characteristics of the EEC and on the placement of the CG and moment of inertia. It also gave the helicopter rescue personnel direct input to the feasibility study. Section 1 describes in detail the design of a one-fifth scale model of the Apollo Command Module Derivative (ACMD) ACRV. The objective of the ACMD Configuration Model Team was to use geometric and dynamic constraints to design a one-fifth scale working model of the Apollo Command Module Derivative (ACMD) configuration with a Lift Attachment Point (LAP) System. This model was required to incorporate a rigidly mounted flotation system and the egress system designed the previous academic year. The LAP system was to be used to determine the dynamic effects of locating the lifting points at different locations on the vehicle. The team was then to build and test the model; however, due to priorities, this did not occur. To better simulate the ACMD after a water landing, the nose cone section was removed and the deck area exposed. The areas researched during the design process were construction, center of gravity and moment of inertia, and lift attachment points

Exploring The Differences In Deep Convective Transport Characteristics Between Quasi-Isolated Strong Convection And Mesoscale Convective Systems Using Seasonal Wrf Simulations

It has been shown in several previous studies that there is a relationship between mesoscale storm type and deep convective mass transport characteristics. For example, a previous simulation study showed that a supercell storm transported significantly more tracers into the stratosphere than did a multicell storm in an environment with identical thermodynamic structure. We utilize the Weather Research and Forecasting (WRF) model (version 3.2.1) with chemistry to simulate mass transport during the convective season of 2007 in the U.S. Southern Great Plains at convection-resolving scale (2 km). The storms that were resolved in the model were then classified using an object-based classification scheme. This classification scheme, which is based on schemes used in the mesoscale observational community, uses model-derived radar reflectivity (a function of precipitation hydrometeors) to classify storm type as either weak convection, quasi-isolated strong convection (QISC), mesoscale convective system (MCS), or linear MCS. This study focuses on examining the differences between the QISC and MCS regimes. Differences on the domain-scale are determined by investigation of two transport parameters: the level of maximum detrainment (LMD) and the magnitude of newly transport mass. Based on total transport over the entire region, results have shown that there are some significant differences between regimes. The LMD is significantly higher in the MCS regime than in the QISC regime in July, but the LMD is very similar in the two regimes in May. Conversely, the magnitude of newly transported mass in the MCS and QISC is very similar in July, but significantly different in May. At a per storm scale, differences were determined by analysis of the magnitude of transport per deeply convective object and the LMD relative to the height of the tropopause. The tropopause-relative LMD followed the domain-wide results, where there were significant differences in July but the regimes transported to similar altitudes in May. There were significant differences in the magnitude of transport per deeply convective object for both May and July

Report of the proceedings of the Colloquium and Workshop on Multiscale Coupled Modeling

The Colloquium and Workshop on Multiscale Coupled Modeling was held for the purpose of addressing modeling issues of importance to planning for the Cooperative Multiscale Experiment (CME). The colloquium presentations attempted to assess the current ability of numerical models to accurately simulate the development and evolution of mesoscale cloud and precipitation systems and their cycling of water substance, energy, and trace species. The primary purpose of the workshop was to make specific recommendations for the improvement of mesoscale models prior to the CME, their coupling with cloud, cumulus ensemble, hydrology, air chemistry models, and the observational requirements to initialize and verify these models

Blood Vessel Tortuosity Selects against Evolution of Agressive Tumor Cells in Confined Tissue Environments: a Modeling Approach

Cancer is a disease of cellular regulation, often initiated by genetic mutation within cells, and leading to a heterogeneous cell population within tissues. In the competition for nutrients and growth space within the tumors the phenotype of each cell determines its success. Selection in this process is imposed by both the microenvironment (neighboring cells, extracellular matrix, and diffusing substances), and the whole of the organism through for example the blood supply. In this view, the development of tumor cells is in close interaction with their increasingly changing environment: the more cells can change, the more their environment will change. Furthermore, instabilities are also introduced on the organism level: blood supply can be blocked by increased tissue pressure or the tortuosity of the tumor-neovascular vessels. This coupling between cell, microenvironment, and organism results in behavior that is hard to predict. Here we introduce a cell-based computational model to study the effect of blood flow obstruction on the micro-evolution of cells within a cancerous tissue. We demonstrate that stages of tumor development emerge naturally, without the need for sequential mutation of specific genes. Secondly, we show that instabilities in blood supply can impact the overall development of tumors and lead to the extinction of the dominant aggressive phenotype, showing a clear distinction between the fitness at the cell level and survival of the population. This provides new insights into potential side effects of recent tumor vasculature renormalization approaches