Observational evidence for relationships between the degree of aggregation of deep convection, water vapor, surface fluxes, and radiation

International audienceTropical deep convection exhibits complex organization over a wide range of scales. This study investigates the relationships between the spatial organization of deep convection and the large-scale atmospheric state. By using several satellite datasets and reanalyses, and by defining a simple diagnostic of convective aggregation, relationships between the degree of convective aggregation and the amount of water vapor, turbulent surface fluxes, and radiation are highlighted above tropical oceans. When deep convection is more aggregated, the middle and upper troposphere are drier in the convection-free environment, turbulent surface fluxes are enhanced, and the low-level and midlevel cloudiness is reduced in the environment. Humidity and cloudiness changes lead to a large increase in outgoing longwave radiation. Cloud changes also result in reduced reflected shortwave radiation. Owing to these opposing effects, the sensitivity of the radiative budget at the top of the atmosphere to convective aggregation turns out to be weak, but the distribution of radiative heating throughout the troposphere is affected. These results suggest that feedbacks between convective aggregation and the large-scale atmospheric state might influence large-scale dynamics and the transports of water and energy and, thus, play a role in the climate variability and change. These observational findings are qualitatively consistent with previous cloud-resolvingmodel results, except for the effects on cloudiness and reflected shortwave radiation. The proposed methodology may be useful for assessing the representation of convective aggregation and its interaction with the large-scale atmospheric state in various numerical models. © 2012 American Meteorological Society

Évaluer et prendre en compte le renforcement orographique

International audienceCe texte présente les premiers résultats obtenus à partir de la base VIRS/PR. Un moyen simple d'analyse des biais systématiques et en particulier des effets orographiques est proposé

Évaluer et prendre en compte le renforcement orographique

International audienceCe texte présente les premiers résultats obtenus à partir de la base VIRS/PR. Un moyen simple d'analyse des biais systématiques et en particulier des effets orographiques est proposé

: Défis actuels et axes de recherche à l'Inria

International audienceCe document est un résumé de la version anglaise du livre blanc d'Inria sur la cybersécurité, qui aété coordonné par Steve Kremer, Ludovic Mé, Didier Rémy et Vincent Roca. La rédaction repose sur la contribution de nombreux scientifiques d'Inria et de ses partenaires. Le livre blanc s'adresse à un large public et a été écrit pour permettre différents niveaux de lecture. Son premier objectif est de présenter l'analyse d'Inria sur les défis en cybersécurité en matière de recherche. À cette fin, il inclut un aperçu général des sujets de recherche académique en cybersécurité et une cartographie des recherches existantes sur la cybersécurité chez Inria. Il comprend aussi des présentations techniques des différents domaines de la cybersécurité et une description détaillée du travail effectué au sein des équipes-projets communes entre Inria et ses partenaires académiques susceptibles d'intéresser des experts en cybersécurité ou toute personne cherchant des informations détaillées sur un sujet particulier. Il se termine par des recommandations générales. Dans ce résumé en français, nous nous concentrons sur les parties générales et stratégiques au détriment des parties techniques et de la cartographie détaillée des recherches menées

Blue light absorption enhancement based on vertically channelling modes in nano-holes arrays

We investigate the specific optical regime occurring at short wavelengths, in the high absorption regime, in silicon thin-films patterned by periodically arranged nano-holes. Near-field scanning optical microscopy indicates that the incoming light is coupled to vertically channelling modes. Optical modelling and simulations show that the light, travelling inside the low-index regions, is absorbed at the direct vicinity of the nano-holes sidewalls. This channelling regime should be taken into account for light management in optoelectronic devices

Does convective aggregation need to be represented in cumulus parameterizations?

Tropical deep convection exhibits a variety of levels of aggregation over a wide range of scales. Based on a multisatellite analysis, the present study shows at mesoscale that different levels of aggregation are statistically associated with differing large-scale atmospheric states, despite similar convective intensity and large-scale forcings. The more aggregated the convection, the dryer and less cloudy the atmosphere, the stronger the outgoing longwave radiation, and the lower the planetary albedo. This suggests that mesoscale convective aggregation has the potential to affect couplings between moisture and convection and between convection, radiation, and large-scale ascent. In so doing, aggregation may play a role in phenomena such as “hot spots” or the Madden-Julian Oscillation. These findings support the need for the representation of mesoscale organization in cumulus parameterizations; most parameterizations used in current climate models lack any such representation. The ability of a cloud system-resolving model to reproduce observed relationships suggests that such models may be useful to guide attempts at parameterizations of convective aggregation

The First 30 years of GEWEX

International audienceAbstract The Global Energy and Water Cycle EXchanges (GEWEX) project was created more than thirty years ago within the framework of the World Climate Research Programme (WCRP). The aim of this initiative was to address major gaps in our understanding of Earth’s energy and water cycles given a lack of information about the basic fluxes and associated reservoirs of these cycles. GEWEX sought to acquire and set standards for climatological data on variables essential for quantifying water and energy fluxes and for closing budgets at the regional and global scales. In so doing, GEWEX activities led to a greatly improved understanding of processes and our ability to predict them. Such understanding was viewed then, as it remains today, essential for advancing weather and climate prediction from global to regional scales. GEWEX has also demonstrated over time the importance of a wider engagement of different communities and the necessity of international collaboration for making progress on understanding and on the monitoring of the changes in the energy and water cycles under ever increasing human pressures. This paper reflects on the first 30 years of evolution and progress that has occurred within GEWEX. This evolution is presented in terms of three main phases of activity. Progress toward the main goals of GEWEX is highlighted by calling out a few achievements from each phase. A vision of the path forward for the coming decade, including the goals of GEWEX for the future, are also described

Measuring global ocean heat content to estimate the earth energy imbalance

The energy radiated by the Earth toward space does not compensate the incoming radiation from the Sun leading to a small positive energy imbalance at the top of the atmosphere (0.4–1 Wm–2). This imbalance is coined Earth’s Energy Imbalance (EEI). It is mostly caused by anthropogenic greenhouse gas emissions and is driving the current warming of the planet. Precise monitoring of EEI is critical to assess the current status of climate change and the future evolution of climate. But the monitoring of EEI is challenging as EEI is two orders of magnitude smaller than the radiation fluxes in and out of the Earth system. Over 93% of the excess energy that is gained by the Earth in response to the positive EEI accumulates into the ocean in the form of heat. This accumulation of heat can be tracked with the ocean observing system such that today, the monitoring of Ocean Heat Content (OHC) and its long-term change provide the most efficient approach to estimate EEI. In this community paper we review the current four state-of-the-art methods to estimate global OHC changes and evaluate their relevance to derive EEI estimates on different time scales. These four methods make use of: (1) direct observations of in situ temperature; (2) satellite-based measurements of the ocean surface net heat fluxes; (3) satellite-based estimates of the thermal expansion of the ocean and (4) ocean reanalyses that assimilate observations from both satellite and in situ instruments. For each method we review the potential and the uncertainty of the method to estimate global OHC changes. We also analyze gaps in the current capability of each method and identify ways of progress for the future to fulfill the requirements of EEI monitoring. Achieving the observation of EEI with sufficient accuracy will depend on merging the remote sensing techniques with in situ measurements of key variables as an integral part of the Ocean Observing System

Estimation of extreme daily precipitation thermodynamic scaling using gridded satellite precipitation products over tropical land

International audienceThis study explores the tropical land distribution of precipitation and its extremes focusing on the daily 1°×1°scale. A common period of 5-year over the tropical belt (30°s-30°n) corresponding to more than 39 million data points, is used to highlight the robust (and non-robust) observed features. A set of 10 observational products is analyzed ranging from satellite only to rain gauges only products and various blended intermediates as well as a sub ensemble of satellite-based products relying upon microwave observations. Overall, the various datasets show a small diversity of response as far as tropical land mean precipitation is concerned. When sorted by surface temperature, the spread in mean rainfall is also well below 10% over a large span of the surface temperature regime. The consistency between the surface temperature and the extreme precipitation is further investigated by computing the thermodynamic scaling of daily precipitation extreme with surface temperature. The wet days' 99.9th and 99th percentiles are considered and corresponds to 'extreme' extremes (∼110 mm d −1) and 'moderate' extremes (∼60 mm d −1), respectively. The analysis reveals three regimes over the 287-305 K 2 m temperature range. In the cold regime, 287-293 K, extremes exhibit no dependence to surface temperature while in the warm regime, 299-305 K, the extremes decrease with temperature as identified in previous studies. Over the 293-299 K regime, the scaling of the sub ensemble of satellite products is ∼5.2 K/% for the 'extremes' extremes and 5.0% for the 'moderate' extremes, and is robust throughout the sub ensemble. This analysis fills the regional gap of previous conventional data based studies and further confirms the Clausius-Clapeyron theoretical expectation for the tropical land regions