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  • Author or Editor: Julien Delanoë x
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Andrew J. Heymsfield
,
Alain Protat
,
Dominique Bouniol
,
Richard T. Austin
,
Robin J. Hogan
,
Julien Delanoë
,
Hajime Okamoto
,
Kaori Sato
,
Gerd-Jan van Zadelhoff
,
David P. Donovan
, and
Zhien Wang

Abstract

Vertical profiles of ice water content (IWC) can now be derived globally from spaceborne cloud satellite radar (CloudSat) data. Integrating these data with Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) data may further increase accuracy. Evaluations of the accuracy of IWC retrieved from radar alone and together with other measurements are now essential. A forward model employing aircraft Lagrangian spiral descents through mid- and low-latitude ice clouds is used to estimate profiles of what a lidar and conventional and Doppler radar would sense. Radar reflectivity Ze and Doppler fall speed at multiple wavelengths and extinction in visible wavelengths were derived from particle size distributions and shape data, constrained by IWC that were measured directly in most instances. These data were provided to eight teams that together cover 10 retrieval methods. Almost 3400 vertically distributed points from 19 clouds were used. Approximate cloud optical depths ranged from below 1 to more than 50. The teams returned retrieval IWC profiles that were evaluated in seven different ways to identify the amount and sources of errors. The mean (median) ratio of the retrieved-to-measured IWC was 1.15 (1.03) ± 0.66 for all teams, 1.08 (1.00) ± 0.60 for those employing a lidar–radar approach, and 1.27 (1.12) ± 0.78 for the standard CloudSat radar–visible optical depth algorithm for Ze > −28 dBZe . The ratios for the groups employing the lidar–radar approach and the radar–visible optical depth algorithm may be lower by as much as 25% because of uncertainties in the extinction in small ice particles provided to the groups. Retrievals from future spaceborne radar using reflectivity–Doppler fall speeds show considerable promise. A lidar–radar approach, as applied to measurements from CALIPSO and CloudSat, is useful only in a narrow range of ice water paths (IWP) (40 < IWP < 100 g m−2). Because of the use of the Rayleigh approximation at high reflectivities in some of the algorithms and differences in the way nonspherical particles and Mie effects are considered, IWC retrievals in regions of radar reflectivity at 94 GHz exceeding about 5 dBZe are subject to uncertainties of ±50%.

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Julien Delanoë
,
Alain Protat
,
Jean-Paul Vinson
,
Williams Brett
,
Christophe Caudoux
,
Fabrice Bertrand
,
Jacques Parent du Chatelet
,
Ruben Hallali
,
Laurent Barthes
,
Martial Haeffelin
, and
Jean-Charles Dupont

Abstract

Doppler cloud radars are amazing tools to characterize cloud and fog properties and to improve their representation in models. However, commercially available cloud radars (35 and 95 GHz) are still very expensive, which hinders their widespread deployment. This study presents the development of a lower-cost semioperational 95-GHz Doppler cloud radar called the Bistatic Radar System for Atmospheric Studies (BASTA). To drastically reduce the cost of the instrument, a different approach is used compared to traditional pulsed radars: instead of transmitting a large amount of energy for a very short time period (as a pulse), a lower amount of energy is transmitted continuously. By using a specific signal processing technique, the radar can challenge expensive radars and provide high-quality measurements of cloud and fog. The latest version of the instrument has a sensitivity of about −50 dBZ at 1 km for 3-s integration and a vertical resolution of 25 m. The BASTA radar currently uses four successive modes for specific applications: the 12.5-m vertical resolution mode is dedicated to fog and low clouds, the 25-m mode is for liquid and ice midtropospheric clouds, and the 100- and 200-m modes are ideal for optically thin high-level ice clouds. The advantages of such a radar for calibration procedures and field operations are also highlighted. The radar comes with a set of products dedicated to cloud and fog studies. For instance, cloud mask, corrected Doppler velocity, and multimode products combining the high-sensitivity mode and high-resolution modes are provided.

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Shuyi S. Chen
,
Brandon W. Kerns
,
Nick Guy
,
David P. Jorgensen
,
Julien Delanoë
,
Nicolas Viltard
,
Christopher J. Zappa
,
Falko Judt
,
Chia-Ying Lee
, and
Ajda Savarin

Abstract

One of the most challenging problems in predicting the Madden–Julian oscillation (MJO) is the initiation of large-scale convective activity associated with the MJO over the tropical Indian Ocean. The lack of observations is a major obstacle. The Dynamics of the MJO (DYNAMO) field campaign collected unprecedented observations from air-, land-, and ship-based platforms from October 2011 to February 2012. Here we provide an overview of the aircraft observations in DYNAMO, which captured an MJO initiation event from November to December 2011. The National Oceanic and Atmospheric Administration (NOAA) WP-3D aircraft was stationed at Diego Garcia and the French Falcon 20 aircraft on Gan Island in the Maldives. Observations from the two aircraft provide a unique dataset of three-dimensional structure of convective cloud systems and their environment from the flight level, airborne Doppler radar, microphysics probes, ocean surface imaging, global positioning system (GPS) dropsonde, and airborne expendable bathythermograph (AXBT) data. The aircraft observations revealed interactions among dry air, the intertropical convergence zone (ITCZ), convective cloud systems, and air–sea interaction induced by convective cold pools, which may play important roles in the multiscale processes of MJO initiation. This overview focuses on some key aspects of the aircraft observations that contribute directly to better understanding of the interactions among convective cloud systems, environmental moisture, and the upper ocean during the MJO initiation over the tropical Indian Ocean. Special emphasis is on the distinct characteristics of convective cloud systems, environmental moisture and winds, air–sea fluxes, and convective cold pools during the convectively suppressed, transition/onset, and active phases of the MJO.

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Dominique Bouniol
,
Alain Protat
,
Julien Delanoë
,
Jacques Pelon
,
Jean-Marcel Piriou
,
François Bouyssel
,
Adrian M. Tompkins
,
Damian R. Wilson
,
Yohann Morille
,
Martial Haeffelin
,
Ewan J. O’Connor
,
Robin J. Hogan
,
Anthony J. Illingworth
,
David P. Donovan
, and
Henk-Klein Baltink

Abstract

The ability of four operational weather forecast models [ECMWF, Action de Recherche Petite Echelle Grande Echelle model (ARPEGE), Regional Atmospheric Climate Model (RACMO), and Met Office] to generate a cloud at the right location and time (the cloud frequency of occurrence) is assessed in the present paper using a two-year time series of observations collected by profiling ground-based active remote sensors (cloud radar and lidar) located at three different sites in western Europe (Cabauw, Netherlands; Chilbolton, United Kingdom; and Palaiseau, France). Particular attention is given to potential biases that may arise from instrumentation differences (especially sensitivity) from one site to another and intermittent sampling. In a second step the statistical properties of the cloud variables involved in most advanced cloud schemes of numerical weather forecast models (ice water content and cloud fraction) are characterized and compared with their counterparts in the models. The two years of observations are first considered as a whole in order to evaluate the accuracy of the statistical representation of the cloud variables in each model. It is shown that all models tend to produce too many high-level clouds, with too-high cloud fraction and ice water content. The midlevel and low-level cloud occurrence is also generally overestimated, with too-low cloud fraction but a correct ice water content. The dataset is then divided into seasons to evaluate the potential of the models to generate different cloud situations in response to different large-scale forcings. Strong variations in cloud occurrence are found in the observations from one season to the same season the following year as well as in the seasonal cycle. Overall, the model biases observed using the whole dataset are still found at seasonal scale, but the models generally manage to well reproduce the observed seasonal variations in cloud occurrence. Overall, models do not generate the same cloud fraction distributions and these distributions do not agree with the observations. Another general conclusion is that the use of continuous ground-based radar and lidar observations is definitely a powerful tool for evaluating model cloud schemes and for a responsive assessment of the benefit achieved by changing or tuning a model cloud parameterization.

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Bjorn Stevens
,
Felix Ament
,
Sandrine Bony
,
Susanne Crewell
,
Florian Ewald
,
Silke Gross
,
Akio Hansen
,
Lutz Hirsch
,
Marek Jacob
,
Tobias Kölling
,
Heike Konow
,
Bernhard Mayer
,
Manfred Wendisch
,
Martin Wirth
,
Kevin Wolf
,
Stephan Bakan
,
Matthias Bauer-Pfundstein
,
Matthias Brueck
,
Julien Delanoë
,
André Ehrlich
,
David Farrell
,
Marvin Forde
,
Felix Gödde
,
Hans Grob
,
Martin Hagen
,
Evelyn Jäkel
,
Friedhelm Jansen
,
Christian Klepp
,
Marcus Klingebiel
,
Mario Mech
,
Gerhard Peters
,
Markus Rapp
,
Allison A. Wing
, and
Tobias Zinner

Abstract

A configuration of the High-Altitude Long-Range Research Aircraft (HALO) as a remote sensing cloud observatory is described, and its use is illustrated with results from the first and second Next-Generation Aircraft Remote Sensing for Validation (NARVAL) field studies. Measurements from the second NARVAL (NARVAL2) are used to highlight the ability of HALO, when configured in this fashion, to characterize not only the distribution of water condensate in the atmosphere, but also its impact on radiant energy transfer and the covarying large-scale meteorological conditions—including the large-scale velocity field and its vertical component. The NARVAL campaigns with HALO demonstrate the potential of airborne cloud observatories to address long-standing riddles in studies of the coupling between clouds and circulation and are helping to motivate a new generation of field studies.

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Véronique Ducrocq
,
Isabelle Braud
,
Silvio Davolio
,
Rossella Ferretti
,
Cyrille Flamant
,
Agustin Jansa
,
Norbert Kalthoff
,
Evelyne Richard
,
Isabelle Taupier-Letage
,
Pierre-Alain Ayral
,
Sophie Belamari
,
Alexis Berne
,
Marco Borga
,
Brice Boudevillain
,
Olivier Bock
,
Jean-Luc Boichard
,
Marie-Noëlle Bouin
,
Olivier Bousquet
,
Christophe Bouvier
,
Jacopo Chiggiato
,
Domenico Cimini
,
Ulrich Corsmeier
,
Laurent Coppola
,
Philippe Cocquerez
,
Eric Defer
,
Julien Delanoë
,
Paolo Di Girolamo
,
Alexis Doerenbecher
,
Philippe Drobinski
,
Yann Dufournet
,
Nadia Fourrié
,
Jonathan J. Gourley
,
Laurent Labatut
,
Dominique Lambert
,
Jérôme Le Coz
,
Frank S. Marzano
,
Gilles Molinié
,
Andrea Montani
,
Guillaume Nord
,
Mathieu Nuret
,
Karim Ramage
,
William Rison
,
Odile Roussot
,
Frédérique Said
,
Alfons Schwarzenboeck
,
Pierre Testor
,
Joël Van Baelen
,
Béatrice Vincendon
,
Montserrat Aran
, and
Jorge Tamayo

The Mediterranean region is frequently affected by heavy precipitation events associated with flash floods, landslides, and mudslides that cause hundreds of millions of euros in damages per year and, often, casualties. A major field campaign was devoted to heavy precipitation and f lash f loods from 5 September to 6 November 2012 within the framework of the 10-yr international Hydrological Cycle in the Mediterranean Experiment (HyMeX) dedicated to the hydrological cycle and related high-impact events. The 2-month field campaign took place over the northwestern Mediterranean Sea and its surrounding coastal regions in France, Italy, and Spain. The observation strategy of the field experiment was devised to improve knowledge of the following key components leading to heavy precipitation and flash flooding in the region: 1) the marine atmospheric f lows that transport moist and conditionally unstable air toward the coasts, 2) the Mediterranean Sea acting as a moisture and energy source, 3) the dynamics and microphysics of the convective systems producing heavy precipitation, and 4) the hydrological processes during flash floods. This article provides the rationale for developing this first HyMeX field experiment and an overview of its design and execution. Highlights of some intensive observation periods illustrate the potential of the unique datasets collected for process understanding, model improvement, and data assimilation.

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Andreas Schäfler
,
George Craig
,
Heini Wernli
,
Philippe Arbogast
,
James D. Doyle
,
Ron McTaggart-Cowan
,
John Methven
,
Gwendal Rivière
,
Felix Ament
,
Maxi Boettcher
,
Martina Bramberger
,
Quitterie Cazenave
,
Richard Cotton
,
Susanne Crewell
,
Julien Delanoë
,
Andreas Dörnbrack
,
André Ehrlich
,
Florian Ewald
,
Andreas Fix
,
Christian M. Grams
,
Suzanne L. Gray
,
Hans Grob
,
Silke Groß
,
Martin Hagen
,
Ben Harvey
,
Lutz Hirsch
,
Marek Jacob
,
Tobias Kölling
,
Heike Konow
,
Christian Lemmerz
,
Oliver Lux
,
Linus Magnusson
,
Bernhard Mayer
,
Mario Mech
,
Richard Moore
,
Jacques Pelon
,
Julian Quinting
,
Stephan Rahm
,
Markus Rapp
,
Marc Rautenhaus
,
Oliver Reitebuch
,
Carolyn A. Reynolds
,
Harald Sodemann
,
Thomas Spengler
,
Geraint Vaughan
,
Manfred Wendisch
,
Martin Wirth
,
Benjamin Witschas
,
Kevin Wolf
, and
Tobias Zinner

Abstract

The North Atlantic Waveguide and Downstream Impact Experiment (NAWDEX) explored the impact of diabatic processes on disturbances of the jet stream and their influence on downstream high-impact weather through the deployment of four research aircraft, each with a sophisticated set of remote sensing and in situ instruments, and coordinated with a suite of ground-based measurements. A total of 49 research flights were performed, including, for the first time, coordinated flights of the four aircraft: the German High Altitude and Long Range Research Aircraft (HALO), the Deutsches Zentrum für Luft- und Raumfahrt (DLR) Dassault Falcon 20, the French Service des Avions Français Instrumentés pour la Recherche en Environnement (SAFIRE) Falcon 20, and the British Facility for Airborne Atmospheric Measurements (FAAM) BAe 146. The observation period from 17 September to 22 October 2016 with frequently occurring extratropical and tropical cyclones was ideal for investigating midlatitude weather over the North Atlantic. NAWDEX featured three sequences of upstream triggers of waveguide disturbances, as well as their dynamic interaction with the jet stream, subsequent development, and eventual downstream weather impact on Europe. Examples are presented to highlight the wealth of phenomena that were sampled, the comprehensive coverage, and the multifaceted nature of the measurements. This unique dataset forms the basis for future case studies and detailed evaluations of weather and climate predictions to improve our understanding of diabatic influences on Rossby waves and the downstream impacts of weather systems affecting Europe.

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