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Vincent Noel
and
Kenneth Sassen

Abstract

This paper presents a study of the orientation of ice crystals in cirrus and midlevel clouds, based on the analysis of several cases of scanning polarization lidar observations. The maximum angle that crystals deviate from the horizontal plane is inferred at consecutive altitude levels by fitting angle-dependent measurements of the linear depolarization ratio and backscattered intensities to a theoretical model with a Gaussian distribution of tilt angles. The average deviation angle is linked to the angular variation of backscatter. A rare observation of so-called Parry-oriented columns is also given to highlight the different backscattering behavior with lidar angle. For planar crystals, two orientation modes are found that depend on cloud temperature. High-level cold (<∼−30°C) clouds show a maximum deviation angle of ∼1.0°, whereas for warmer (>∼−20°C) midlevel clouds this angle averages ∼2.0°. This difference is caused by variations in particle shape and fall attitude that depend on temperature, likely involving a transition from simple plates to more widely fluttering dendrites at the warmer temperatures. Polarization lidar scans are clearly uniquely suited for the study of ice crystal orientations in clouds.

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Vincent Noel
and
Hélène Chepfer

Abstract

The goal of this paper is to retrieve information about ice particle orientation in cirrus clouds. This is achieved by comparing simulations of sunlight reflection on a cirrus cloud with measurements of polarized radiances from the spaceborne instrument Polarization and Directionality of the Earth's Reflectance (POLDER-1) on Advanced Earth Observing Satellite-1 (ADEOS-1). Results show that horizontal orientation of crystals can be spotted by the presence of a local maximum of polarized radiance in the direction of specular reflection. The angular width of the local maximum is shown to contain information on the particle maximum deviation angle, while the maximum intensity can provide information on particle shape and relative concentrations of ice crystals, horizontally and randomly oriented. The study of 31 ice cloud cases show that in 80% of them, the deviation angle is less than 3°. Also, the relative concentration of horizontally oriented crystals is less than 21%, depending on the angular distribution used for crystal deviation.

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Vincent Noel
,
Helene Chepfer
,
Martial Haeffelin
, and
Yohann Morille

Abstract

This paper presents a study of ice crystal shapes in midlatitude ice clouds inferred from a technique based on the comparison of ray-tracing simulations with lidar depolarization ratio measured at 532 nm. This technique is applied to three years of lidar depolarization ratio observations from the Site Instrumental de Recherche par Télédétection Atmosphérique (SIRTA) observatory in Palaiseau, France, amounting to 322 different days of ice cloud observations. Particles in clouds are classified in three major groups: plates, columns, and irregular shapes with aspect ratios close to unity. Retrieved shapes are correlated with radiosounding observations from a close-by meteorological station: temperature, relative humidity, wind speed, and direction.

Results show a strong dependence of the relative concentration of different crystal shapes to most atmospheric variables, such as the temperature, with a clear successive dominance by platelike (temperature above −20°C), irregular (temperatures between −60° and −40°C), and columnlike shapes (temperatures below −60°C). Particle shapes are almost exclusively columnlike below −75°C. This is in sharp contrast with previous results of the same classification applied to tropical clouds, and highlights the high geographic variability of the ice clouds distribution of microphysical properties. Results also suggest that ice clouds created by jet streams (identified by high wind speeds) are strongly dominated by columnlike shapes, while front-created ice clouds (identified by lower wind speeds) show a much more variable mix of shapes, with the dominant shapes depending on other factors. Results also suggest different microphysical properties according to the average direction source of air masses and winds. Following these results, a possible parameterization of ice crystal shapes in midlatitude ice clouds as a function of temperature is provided.

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Andrew D. Gronewold
,
Vincent Fortin
,
Robert Caldwell
, and
James Noel

Abstract

Monitoring, understanding, and forecasting the hydrologic cycle of large freshwater basins often requires a broad suite of data and models. Many of these datasets and models, however, are susceptible to variations in monitoring infrastructure and data dissemination protocols when watershed, political, and jurisdictional boundaries do not align. Reconciling hydrometeorological monitoring gaps and inconsistencies across the international Laurentian Great Lakes–St. Lawrence River basin is particularly challenging because of its size and because the basin’s dominant hydrologic feature is the vast surface waters of the Great Lakes.

For tens of millions of Canadian and U.S. residents that live within the Great Lakes basin, seamless binational datasets are needed to better understand and predict coastal water-level fluctuations and other conditions that could potentially threaten human and environmental health. Binational products addressing this need have historically been developed and maintained by the Coordinating Committee on Great Lakes Basic Hydraulic and Hydrologic Data (Coordinating Committee). The Coordinating Committee recently held its one-hundredth semiannual meeting and reflected on a range of historical accomplishments while setting goals for future work. This article provides a synthesis of those achievements and goals. Particularly significant legacy and recently developed datasets of the Coordinating Committee include historical Great Lakes surface water elevations, basin-scale tributary inflow to the Great Lakes, and basin-scale estimates of both over-lake and over-land precipitation. Moving forward, members of the Coordinating Committee will work toward customizing state-of-the-art hydrologic and meteorological forecasting systems across the entire Great Lakes basin and toward promoting their products and protocols as templates for successful binational coordination across other large binational freshwater basins.

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Anna E. Luebke
,
Julien Delanoë
,
Vincent Noel
,
Hélène Chepfer
, and
Bjorn Stevens
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Adrien Lacour
,
Helene Chepfer
,
Matthew D. Shupe
,
Nathaniel B. Miller
,
Vincent Noel
,
Jennifer Kay
,
David D. Turner
, and
Rodrigo Guzman

Abstract

Spaceborne lidar observations from the Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite provide the first-ever observations of cloud vertical structure and phase over the entire Greenland Ice Sheet. This study leverages CALIPSO observations over Greenland to pursue two investigations. First, the GCM-Oriented CALIPSO Cloud Product (CALIPSO-GOCCP) observations are compared with collocated ground-based radar and lidar observations at Summit, Greenland. The liquid cloud cover agrees well between the spaceborne and ground-based observations. In contrast, ground–satellite differences reach 30% in total cloud cover and 40% in cloud fraction below 2 km above ground level, due to optically very thin ice clouds (IWC < 2.5 × 10−3 g m−3) missed by CALIPSO-GOCCP. Those results are compared with satellite cloud climatologies from the GEWEX cloud assessment. Most passive sensors detect fewer clouds than CALIPSO-GOCCP and the Summit ground observations, due to different detection methods. Second, the distribution of clouds over the Greenland is analyzed using CALIPSO-GOCCP. Central Greenland is the cloudiest area in summer, at +7% and +4% above the Greenland-wide average for total and liquid cloud cover, respectively. Southern Greenland contains free-tropospheric thin ice clouds in all seasons and liquid clouds in summer. In northern Greenland, fewer ice clouds are detected than in other areas, but the liquid cloud cover seasonal cycle in that region drives the total Greenland cloud annual variability with a maximum in summer. In 2010 and 2012, large ice-sheet melting events have a positive liquid cloud cover anomaly (from +1% to +2%). In contrast, fewer clouds (−7%) are observed during low ice-sheet melt years (e.g., 2009).

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Florence Rabier
,
Aurélie Bouchard
,
Eric Brun
,
Alexis Doerenbecher
,
Stéphanie Guedj
,
Vincent Guidard
,
Fatima Karbou
,
Vincent-Henri Peuch
,
Laaziz El Amraoui
,
Dominique Puech
,
Christophe Genthon
,
Ghislain Picard
,
Michael Town
,
Albert Hertzog
,
François Vial
,
Philippe Cocquerez
,
Stephen A. Cohn
,
Terry Hock
,
Jack Fox
,
Hal Cole
,
David Parsons
,
Jordan Powers
,
Keith Romberg
,
Joseph VanAndel
,
Terry Deshler
,
Jennifer Mercer
,
Jennifer S. Haase
,
Linnea Avallone
,
Lars Kalnajs
,
C. Roberto Mechoso
,
Andrew Tangborn
,
Andrea Pellegrini
,
Yves Frenot
,
Jean-Noël Thépaut
,
Anthony McNally
,
Gianpaolo Balsamo
, and
Peter Steinle

The Concordiasi project is making innovative observations of the atmosphere above Antarctica. The most important goals of the Concordiasi are as follows:

  • To enhance the accuracy of weather prediction and climate records in Antarctica through the assimilation of in situ and satellite data, with an emphasis on data provided by hyperspectral infrared sounders. The focus is on clouds, precipitation, and the mass budget of the ice sheets. The improvements in dynamical model analyses and forecasts will be used in chemical-transport models that describe the links between the polar vortex dynamics and ozone depletion, and to advance the under understanding of the Earth system by examining the interactions between Antarctica and lower latitudes.

  • To improve our understanding of microphysical and dynamical processes controlling the polar ozone, by providing the first quasi-Lagrangian observations of stratospheric ozone and particles, in addition to an improved characterization of the 3D polar vortex dynamics. Techniques for assimilating these Lagrangian observations are being developed.

A major Concordiasi component is a field experiment during the austral springs of 2008–10. The field activities in 2010 are based on a constellation of up to 18 long-duration stratospheric super-pressure balloons (SPBs) deployed from the McMurdo station. Six of these balloons will carry GPS receivers and in situ instruments measuring temperature, pressure, ozone, and particles. Twelve of the balloons will release dropsondes on demand for measuring atmospheric parameters. Lastly, radiosounding measurements are collected at various sites, including the Concordia station.

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Vincent-Henri Peuch
,
Richard Engelen
,
Michel Rixen
,
Dick Dee
,
Johannes Flemming
,
Martin Suttie
,
Melanie Ades
,
Anna Agustí-Panareda
,
Cristina Ananasso
,
Erik Andersson
,
David Armstrong
,
Jérôme Barré
,
Nicolas Bousserez
,
Juan Jose Dominguez
,
Sébastien Garrigues
,
Antje Inness
,
Luke Jones
,
Zak Kipling
,
Julie Letertre-Danczak
,
Mark Parrington
,
Miha Razinger
,
Roberto Ribas
,
Stijn Vermoote
,
Xiaobo Yang
,
Adrian Simmons
,
Juan Garcés de Marcilla
, and
Jean-Noël Thépaut

Abstract

The Copernicus Atmosphere Monitoring Service (CAMS), part of the European Union’s Earth observation program Copernicus, entered operations in July 2015. Implemented by the European Centre for Medium-Range Weather Forecasts (ECMWF) as a truly European effort with over 23,500 direct data users and well over 200 million end users worldwide as of March 2022, CAMS delivers numerous global and regional information products about air quality, inventory-based emissions and observation-based surface fluxes of greenhouse gases and from biomass burning, solar energy, ozone and UV radiation, and climate forcings. Access to CAMS products is open and free of charge via the Atmosphere Data Store. The CAMS global atmospheric composition analyses, forecasts, and reanalyses build on ECMWF’s Integrated Forecasting System (IFS) and exploit over 90 different satellite data streams. The global products are complemented by coherent higher-resolution regional air quality products over Europe derived from multisystem analyses and forecasts. CAMS information products also include policy support such as quantitative impact assessment of short- and long-term pollutant-emission mitigation scenarios, source apportionment information, and annual European air quality assessment reports. Relevant CAMS products are cited and used for instance in IPCC Assessment Reports. Providing dedicated support for users operating smartphone applications, websites, or TV bulletins in Europe and worldwide is also integral to the service. This paper presents key achievements of the CAMS initial phase (2014–21) and outlines some of its new components for the second phase (2021–28), e.g., the new Copernicus anthropogenic CO2 emissions Monitoring and Verification Support capacity that will monitor global anthropogenic emissions of key greenhouse gases.

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Florence Rabier
,
Steve Cohn
,
Philippe Cocquerez
,
Albert Hertzog
,
Linnea Avallone
,
Terry Deshler
,
Jennifer Haase
,
Terry Hock
,
Alexis Doerenbecher
,
Junhong Wang
,
Vincent Guidard
,
Jean-Noël Thépaut
,
Rolf Langland
,
Andrew Tangborn
,
Gianpaolo Balsamo
,
Eric Brun
,
David Parsons
,
Jérôme Bordereau
,
Carla Cardinali
,
François Danis
,
Jean-Pierre Escarnot
,
Nadia Fourrié
,
Ron Gelaro
,
Christophe Genthon
,
Kayo Ide
,
Lars Kalnajs
,
Charlie Martin
,
Louis-François Meunier
,
Jean-Marc Nicot
,
Tuuli Perttula
,
Nicholas Potts
,
Patrick Ragazzo
,
David Richardson
,
Sergio Sosa-Sesma
, and
André Vargas
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