Electrical sensing of the dynamical structure of the planetary boundary layer

Turbulent and convective processes within the planetary boundary layer are responsible for the transport of moisture, momentum and particulate matter, but are also important in determining the electrical charge transport of the lower atmosphere. This paper presents the first high resolution vertical charge profiles during fair weather conditions obtained with instrumented radiosonde balloons over Alqueva, Portugal during the summer of 2014. The short intervals (4 hours) between balloon flights enabled the diurnal variation in the vertical profile of charge within the boundary layer to be examined in detail, with much smaller charges (up to 20pCm-3) observed during stable night time periods than during the day. Following sunrise, the evolution of the charge profile was complex, demonstrating charged ultrafine aerosol, lofted upwards by daytime convection. This produced charge up to 92pCm-3 up to 500m above the surface. The diurnal variation in the integrated column of charge above the site tracked closely with the diurnal variation in near surface charge as derived from a nearby electric field mill, confirming the importance of the link between surface charge generation processes and aloft. The local aerosol vertical profiles were estimated using backscatter measurements from a collocated ceilometer. These were utilised in a simple model to calculate the charge expected due to vertical conduction current flow in the global electric circuit through aerosol layers. The analysis presented here demonstrates that charge can provide detailed information about boundary layer transport, particularly in regard to the ultrafine aerosol structure, that conventional thermodynamic and ceilometer measurements do not

Intercomparison of methods of coupling between convection and large-scale circulation: 1. Comparison over uniform surface conditions

As part of an international intercomparison project, a set of single column models (SCMs) and cloud-resolving models (CRMs) are run under the weak temperature gradient (WTG) method and the damped gravity wave (DGW) method. For each model, the implementation of the WTG or DGW method involves a simulated column which is coupled to a reference state defined with profiles obtained from the same model in radiative-convective equilibrium. The simulated column has the same surface conditions as the reference state and is initialized with profiles from the reference state. We performed systematic comparison of the behavior of different models under a consistent implementation of the WTG method and the DGW method and systematic comparison of the WTG and DGW methods in models with different physics and numerics. CRMs and SCMs produce a variety of behaviors under both WTG and DGW methods. Some of the models reproduce the reference state while others sustain a large-scale circulation which results in either substantially lower or higher precipitation compared to the value of the reference state. CRMs show a fairly linear relationship between precipitation and circulation strength. SCMs display a wider range of behaviors than CRMs. Some SCMs under the WTG method produce zero precipitation. Within an individual SCM, a DGW simulation and a corresponding WTG simulation can produce different signed circulation. When initialized with a dry troposphere, DGW simulations always result in a precipitating equilibrium state. The greatest sensitivities to the initial moisture conditions occur for multiple stable equilibria in some WTG simulations, corresponding to either a dry equilibrium state when initialized as dry or a precipitating equilibrium state when initialized as moist. Multiple equilibria are seen in more WTG simulations for higher SST. In some models, the existence of multiple equilibria is sensitive to some parameters in the WTG calculations

High power high frequency soft switching converter using serial connected switches

International audienceThis paper presents a chopper topology suitable for high voltage, with a switch made of serial connected power devices. Serial connection of power components encounters two major problems in hard switching : voltage unbalance and overcurrents at turn on due to parasitic capacitances to ground. The proposed topology takes advantage of soft switching to reduce both problems by a suitable utilisation of inductors and capacitors. A converter tested at 9kV input voltage is also presented

High voltage fast switches for nuclear applications

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High reliability high voltage fast switches

International audienceIn France, one joint program between Commissariat à l'Energie Atomique (C.E.A.) for the research part and COGEMA for the industrial application is the development of the Uranium Vapor Laser Isotopic Separation (SILVA). The Power Electronic Laboratory from the C.E.A. in Pierrelatte is in charge of development on power supplies for Copper Vapor Lasers. For this specific application, the association of thousands of small standard components on printed circuit board is a cost-effective and reliable solution. We will explain why this solution is a costeffective and high-performance one for this application. Moreover, we will see that, in our particular case, the serial connection of a large number of components provides a very high reliability without over-cost

Serial connected active voltage clamping

International audienceThe new post project for uranium enrichment SILVA needs specific power converters. The LETC laboratory of the C.E.A. in Pierrelatte has been studying these since 5 years. The aim of this laboratory consists in developing high voltage solid-state converters using a large number of small standard solidstate components (MOSFETs, IGBTs, thyristors and diodes) connected in series. In these associations, voltage balancement system are not used, but the voltage is limited on each stage in its safety area by clamping protection. This paper describes different voltage clamping systems, active clamping technique and their association in series

Short circuit of a high voltage high current MOSFET MATRIX Switch

International audienceIn France, one joint program between Commissariat à l'Energie Atomique (C.E.A.) for the research part and COGEMA for the industrial application is the development of the Uranium Vapor Laser Isotopic Separation (SILVA). The Power Electronic Laboratory from the C.E.A. in Pierrelatte is in charge of development on power supplies for Copper Vapor Lasers. For this application, the strategy of the laboratory is the association of thousands of small standard components on printed circuit board as a cost-effective high performance and reliable solution. For PCIM, in 1999, [1] we presented a Keynote-paper about the strategy of the laboratory and we gave an overview of some different switches with MOSFETs, IGBTs, Thyristors, Diodes and nanosecond switches with standard MOSFETs. The three first switches are very fast turnon switches for capacitor lines or pulse forming network discharge applications. These three switches are not designed to switch off a high level of current. For high voltage very fast applications, turn-off switches are very difficult because of short circuit. The inductance is low, so it is necessary for the switch to limit the current and to open this short-circuit current. Now, we have a new fast 500 A MOSFETs MATRIX switch for high voltage modulator with a very good short-circuit behavior. We present this new switch :-500 A 10 kV module switch short circuit behavior high voltage fast modulator design some industrial applications