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Emma Järvinen
,
Martin Schnaiter
,
Guillaume Mioche
,
Olivier Jourdan
,
Valery N. Shcherbakov
,
Anja Costa
,
Armin Afchine
,
Martina Krämer
,
Fabian Heidelberg
,
Tina Jurkat
,
Christiane Voigt
,
Hans Schlager
,
Leonid Nichman
,
Martin Gallagher
,
Edwin Hirst
,
Carl Schmitt
,
Aaron Bansemer
,
Andy Heymsfield
,
Paul Lawson
,
Ugo Tricoli
,
Klaus Pfeilsticker
,
Paul Vochezer
,
Ottmar Möhler
, and
Thomas Leisner

Abstract

Homogeneous freezing of supercooled droplets occurs in convective systems in low and midlatitudes. This droplet-freezing process leads to the formation of a large amount of small ice particles, so-called frozen droplets, that are transported to the upper parts of anvil outflows, where they can influence the cloud radiative properties. However, the detailed microphysics and, thus, the scattering properties of these small ice particles are highly uncertain. Here, the link between the microphysical and optical properties of frozen droplets is investigated in cloud chamber experiments, where the frozen droplets were formed, grown, and sublimated under controlled conditions. It was found that frozen droplets developed a high degree of small-scale complexity after their initial formation and subsequent growth. During sublimation, the small-scale complexity disappeared, releasing a smooth and near-spherical ice particle. Angular light scattering and depolarization measurements confirmed that these sublimating frozen droplets scattered light similar to spherical particles: that is, they had angular light-scattering properties similar to water droplets. The knowledge gained from this laboratory study was applied to two case studies of aircraft measurements in midlatitude and tropical convective systems. The in situ aircraft measurements confirmed that the microphysics of frozen droplets is dependent on the humidity conditions they are exposed to (growth or sublimation). The existence of optically spherical frozen droplets can be important for the radiative properties of detraining convective outflows.

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Manfred Wendisch
,
Ulrich Pöschl
,
Meinrat O. Andreae
,
Luiz A. T. Machado
,
Rachel Albrecht
,
Hans Schlager
,
Daniel Rosenfeld
,
Scot T. Martin
,
Ahmed Abdelmonem
,
Armin Afchine
,
Alessandro C. Araùjo
,
Paulo Artaxo
,
Heinfried Aufmhoff
,
Henrique M. J. Barbosa
,
Stephan Borrmann
,
Ramon Braga
,
Bernhard Buchholz
,
Micael Amore Cecchini
,
Anja Costa
,
Joachim Curtius
,
Maximilian Dollner
,
Marcel Dorf
,
Volker Dreiling
,
Volker Ebert
,
André Ehrlich
,
Florian Ewald
,
Gilberto Fisch
,
Andreas Fix
,
Fabian Frank
,
Daniel Fütterer
,
Christopher Heckl
,
Fabian Heidelberg
,
Tilman Hüneke
,
Evelyn Jäkel
,
Emma Järvinen
,
Tina Jurkat
,
Sandra Kanter
,
Udo Kästner
,
Mareike Kenntner
,
Jürgen Kesselmeier
,
Thomas Klimach
,
Matthias Knecht
,
Rebecca Kohl
,
Tobias Kölling
,
Martina Krämer
,
Mira Krüger
,
Trismono Candra Krisna
,
Jost V. Lavric
,
Karla Longo
,
Christoph Mahnke
,
Antonio O. Manzi
,
Bernhard Mayer
,
Stephan Mertes
,
Andreas Minikin
,
Sergej Molleker
,
Steffen Münch
,
Björn Nillius
,
Klaus Pfeilsticker
,
Christopher Pöhlker
,
Anke Roiger
,
Diana Rose
,
Dagmar Rosenow
,
Daniel Sauer
,
Martin Schnaiter
,
Johannes Schneider
,
Christiane Schulz
,
Rodrigo A. F. de Souza
,
Antonio Spanu
,
Paul Stock
,
Daniel Vila
,
Christiane Voigt
,
Adrian Walser
,
David Walter
,
Ralf Weigel
,
Bernadett Weinzierl
,
Frank Werner
,
Marcia A. Yamasoe
,
Helmut Ziereis
,
Tobias Zinner
, and
Martin Zöger

Abstract

Between 1 September and 4 October 2014, a combined airborne and ground-based measurement campaign was conducted to study tropical deep convective clouds over the Brazilian Amazon rain forest. The new German research aircraft, High Altitude and Long Range Research Aircraft (HALO), a modified Gulfstream G550, and extensive ground-based instrumentation were deployed in and near Manaus (State of Amazonas). The campaign was part of the German–Brazilian Aerosol, Cloud, Precipitation, and Radiation Interactions and Dynamics of Convective Cloud Systems–Cloud Processes of the Main Precipitation Systems in Brazil: A Contribution to Cloud Resolving Modeling and to the GPM (Global Precipitation Measurement) (ACRIDICON– CHUVA) venture to quantify aerosol–cloud–precipitation interactions and their thermodynamic, dynamic, and radiative effects by in situ and remote sensing measurements over Amazonia. The ACRIDICON–CHUVA field observations were carried out in cooperation with the second intensive operating period of Green Ocean Amazon 2014/15 (GoAmazon2014/5). In this paper we focus on the airborne data measured on HALO, which was equipped with about 30 in situ and remote sensing instruments for meteorological, trace gas, aerosol, cloud, precipitation, and spectral solar radiation measurements. Fourteen research flights with a total duration of 96 flight hours were performed. Five scientific topics were pursued: 1) cloud vertical evolution and life cycle (cloud profiling), 2) cloud processing of aerosol particles and trace gases (inflow and outflow), 3) satellite and radar validation (cloud products), 4) vertical transport and mixing (tracer experiment), and 5) cloud formation over forested/deforested areas. Data were collected in near-pristine atmospheric conditions and in environments polluted by biomass burning and urban emissions. The paper presents a general introduction of the ACRIDICON– CHUVA campaign (motivation and addressed research topics) and of HALO with its extensive instrument package, as well as a presentation of a few selected measurement results acquired during the flights for some selected scientific topics.

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Katharine S. Law
,
Andreas Stohl
,
Patricia K. Quinn
,
Charles A. Brock
,
John F. Burkhart
,
Jean-Daniel Paris
,
Gerard Ancellet
,
Hanwant B. Singh
,
Anke Roiger
,
Hans Schlager
,
Jack Dibb
,
Daniel J. Jacob
,
Steve R. Arnold
,
Jacques Pelon
, and
Jennie L. Thomas

Given the rapid nature of climate change occurring in the Arctic and the difficulty climate models have in quantitatively reproducing observed changes such as sea ice loss, it is important to improve understanding of the processes leading to climate change in this region, including the role of short-lived climate pollutants such as aerosols and ozone. It has long been known that pollution produced from emissions at midlatitudes can be transported to the Arctic, resulting in a winter/spring aerosol maximum known as Arctic haze. However, many uncertainties remain about the composition and origin of Arctic pollution throughout the troposphere; for example, many climate–chemistry models fail to reproduce the strong seasonality of aerosol abundance observed at Arctic surface sites, the origin and deposition mechanisms of black carbon (soot) particles that darken the snow and ice surface in the Arctic is poorly understood, and chemical processes controlling the abundance of tropospheric ozone are not well quantified. The International Polar Year (IPY) Polar Study using Aircraft, Remote Sensing, Surface Measurements and Models, Climate, Chemistry, Aerosols and Transport (POLARCAT) core project had the goal to improve understanding about the origins of pollutants transported to the Arctic; to detail the chemical composition, optical properties, and climate forcing potential of Arctic aerosols; to evaluate the processes governing tropospheric ozone; and to quantify the role of boreal forest fires. This article provides a review of the many results now available based on analysis of data collected during the POLARCAT aircraft-, ship-, and ground-based field campaigns in spring and summer 2008. Major findings are highlighted and areas requiring further investigation are discussed.

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